Title of Invention	A MAGNETIC COMPOSITE FOR AC APPLICATIONS AND A PROCESS FOR MANUFACTURING THE SAME
Abstract	A magnetic composite for AC applications with improved magnetic properties (i.e. low hysteresis losses and low eddy current losses) is disclosed. The composite comprises a consolidation of magnetizable metallic microlamellar particles each having a top ad bottom surfaces and opposite ends. The top and bottom surfaces are coated with a dielectric coating for increasing the resistivity of the composite and reducing eddy current losses. The dielectric coating is made of a refractory material and the ends of the lamellar particles are metallurgically bonded to each other to reduce hysteresis losses of the composite. A process for manufacturing the same is also disclosed. The composite is suitable for manufacturing devices for AC applications such as transformers, stator and rotor of motors, generators, alternators, field concentrators, chokes, relays, electromechanical actuators, synchroresolvers, etc.

Title of Invention

A MAGNETIC COMPOSITE FOR AC APPLICATIONS AND A PROCESS FOR MANUFACTURING THE SAME

Abstract

A magnetic composite for AC applications with improved magnetic properties (i.e. low hysteresis losses and low eddy current losses) is disclosed. The composite comprises a consolidation of magnetizable metallic microlamellar particles each having a top ad bottom surfaces and opposite ends. The top and bottom surfaces are coated with a dielectric coating for increasing the resistivity of the composite and reducing eddy current losses. The dielectric coating is made of a refractory material and the ends of the lamellar particles are metallurgically bonded to each other to reduce hysteresis losses of the composite. A process for manufacturing the same is also disclosed. The composite is suitable for manufacturing devices for AC applications such as transformers, stator and rotor of motors, generators, alternators, field concentrators, chokes, relays, electromechanical actuators, synchroresolvers, etc.

Full Text	A MAGNETIC COMPOSITE FOR AC APPLICATIONS AND A PROCESS FOR MANUFACTURING THE SAME FIELD OF THE INVENTION The present invention relates generally to the field of magnetic materials, more specifically to soft or temporary magnetic composites for AC applications and to the production of the same. More particularly, it concerns a soft magnetic composite with reduced hysteresis and eddy current losses and very good mechanical properties. The magnetic composite of the invention is well suited for manufacturing power application devices such as stator or rotor of machines or parts of relays operating at frequencies up to 10 000 Hz; or chokes, inductors or transformers for frequencies up to 10 000 Hz. BACKGROUND OF THE INVENTION Magnetic materials can be divided into two major classes: permanent magnetic materials (also referred to as hard magnetic materials) and temporary magnetic materials (also referred to as soft magnetic materials). The permanent magnets are characterized by a large remanence, so that after removal of a magnetizing force, a high flux density remains. The permanent magnets tend toward large hysteresis loops, which are the closed curves showing the variation of the magnetic induction of a magnetic material with the external magnetic field producing it when this field is changed through a complete cycle. Permanent magnets are commonly physically hard substances and are, therefore, called hard magnets. The temporary or soft magnets have low values of remanence and small hysteresis loops. They are commonly physically softer than the hard magnets and are known as soft magnets. Ideally, the soft magnets should have large values of permeability () up to a high saturated flux density. The value of the permeability () is the ratio B/H, where H represents the applied magnetic field, or magnetic force, expressed in amperes per meter (A/M) and B is the magnetic flux density induced in the material, and it is expressed in teslas (one tesla being equal to one weber per meter square (W/m2)). Soft magnetic materials are usually for applications where they have to canalize a varying magnetic flux. They are conventionally used for manufacturing transformers, inductance for electronic circuits, magnetic screens, stator and rotor of motors, generators, alternators, field concentrators, synchroresolver, etc. A soft magnetic material has to rapidly react to the small variations of an external inducing magnetic field, and that, without heating and without affecting the frequency of the external field. Therefore, soft magnets are usually used with alternating currents, and for maximum efficiency, it is essential to minimize the energy losses associated with the changing electric field. The energy losses, or core losses, as they are sometimes called, result in conversion of electric energy to thermal energy. The losses are usually expressed in terms of watts/kg (W/kg) for a given flux density (in teslas) at a given frequency (in Hertz). There are two principal mechanisms by which energy or core losses occur. These are hysteresis losses and eddy current losses. Soft magnetic materials have to have a small hysteresis loop (a small coercive field Hc) and a high flux density (B) at saturation. As well explained in US 6,548,012, hysteresis losses are due to the energy dissipated by the wall domain movement and they are proportional to the frequency. They are influenced by the chemical composition and the structure of the material. Eddy currents are induced when a magnetic field is exposed to an alternating magnetic field. These currents which travel normal to the direction of the magnetic flux lead to an energy loss through Joule (resistance) heating. Eddy current losses are expected to vary with the square of the frequency, and inversely with the resistivity. The relative importance of the eddy current losses thus depends on the electrical resistivity of the material. In prior art, soft magnetic parts for alternative current of low and medium frequency applications (between 50 Hz and 50 000 Hz) have been produced using basically two different technologies, each having their advantages and limitations. The first and widely used, since the end of the 19th century, consists of punching and stacking steel laminations. This well-known process involves material loss since scrap material is generated from notches and edges of the laminations when stamping. This material loss could be very costly with some specific alloys. This process also requires a default free roll of material of dimensions greater than the dimensions of the part to be produced. The laminations have the final geometry or a subdivision of the final geometry of the parts and can be coated with an organic and/or inorganic insulating material. Every imperfection on the laminations like edges burr decreases the stacking factor of the final part and thus its maximum induction. Also, mass production of laminations prevents design with rounded edges to help copper wire winding. Due to the planar nature of the laminations, their use limits the design of devices with 2 dimensions distribution of the magnetic field. Indeed, the field is limited to travel only in the plane of the laminations. The cost of the laminations is related to their thickness. To limit energy losses generated by eddy currents, as the magnetic field frequency of the application increases, laminations thickness must be decreased. This increases the rolling cost of the material and decreases the stacking factor of the final part due to imperfect surface finish of the laminations and burrs and the relative importance of the insulating coating. Laminations are thus well suited but limited to low frequency applications. The second process for the production of soft magnetic parts for AC applications, well-known since the beginning of the 20th century, is a variant of the mass production powder metallurgy process where particles used are electrically isolated from each other by a coating (US Patents 421,067; 1,669,649; 1,789,477; 1,850,181; 1,859,067; 1,878,589; 2,330,590; 2,783,208; 4,543,208; 5,063,011; 5,211,896). To prevent the formation of electrical contacts between the powder particles, and thus to reduce the eddy current losses, the powder particles are not sintered for AC applications. Parts issued from this process are commonly named "soft magnetic composites or SMC". Obviously, this process has the advantage of eliminating material loss. SMC are isotropic and thus offer the possibility of designing components which allow the magnetic fields to move in the three dimensions. SMC allow also the production of rounded edges with conventional powder metallurgy pressing techniques. As mentioned above, those rounded edges help winding the electric conductors. Due to the higher curvature radius of the rounded edges, the electrical conductors require less insulation. Furthermore, a reduction in the length of the conductors due to the rounded edges of the soft magnetic part is a great advantage, since it allows the amount of copper used to be minimized as well as the copper loss (loss due to the electrical resistivity of the electrical conductor carrying the current in the electromagnetic device). With rounded edges, the overall dimension of the electrical component could be reduced, since electrical winding could be partially inlaid within the volume normally occupied by the soft magnetic part. In addition, due to the isotropy of t the material and the gain of freedom of the pressing process, new designs that increase total yield, decrease the volume or the weight for the same power output of electric machines are possible, since a better distribution or movement of the magnetic field in the three dimensions is possible. Another advantage of the powder metallurgy process is the elimination of the clamping mean needed to secure laminations together in the final part. With laminations, clamping is sometimes replaced by a welding of the edges of laminations. Using the later approach, the eddy currents are considerably increased, and the total yield of the device or its frequency range application is decreased. The limitation of the SMC is their high hysteresis losses and low permeability compared to steel laminations. Since particles must be insulated from each other to limit eddy currents induction, there is a distributed air gap in the material that decreases significantly the magnetic permeability and increases the coercive field. Additionally, to prevent the destruction of the insulation or coating, SMC can very hardly be fully annealed or achieve a complete recrystallisation with grain coarsening. The temperatures reported for annealing SMC without loosing insulation are about 600°C in a non-reducing atmosphere and with the use of partially or totally inorganic coating (US Patents 2,230,228; 4,601,765; 4,602,957; 5,595,609; 5,754,936; 6,251,514; 6,331,270 B1; PCT/SE96/00397). Although the annealing temperature commonly used is not sufficient to completely remove residual strain in the particles or to cause recrystallisation or grain growth, a substantial amelioration of the hysteresis losses is observed. Ultimately, for all the soft magnetic composites with irregular or spherical particles developed for AC applications until now, even if residual strain would have been removed and grain growth would have been possible at temperatures used for the annealing cycle of finished parts, metallic grain dimension is limited to the size of the particles. This small grain size limits the possibility of increasing the permeability, decreasing the coercive field or simply, the hysteresis losses in the material. Indeed, the smaller the metallic grains are, the higher is the number of grain boundaries, and more energy is required for moving the magnetic domain walls and increasing the induction of the material in one direction. Therefore, the resulting total energy losses (or core losses) of SMC parts at low frequency (below 400Hz) is greater than the total energy losses obtained with laminations. The low permeability values require also more copper wire to achieve the same induction or torque in the electromagnetic device. An optimized three dimensions and rounded winding edges design of the part made with the SMC with irregular or spherical particles can partially or completely compensate those higher hysteresis losses and low permeability values encountered with SMC material at low frequency. Some attempts have been made to develop more performing inorganic coatings and processes for conventional soft magnetic composites that would allow a full annealing of compacts and even recrystallisation without losing too much electrical insulation between particles (US Patents 2,937,964; 5,352,522; EP 0 088 992 A2; WO 02/058865). These prior art documents teach a heat treatment at around 1000°C or less to consolidate particles by the diffusion or interaction of the insulating material of each particle. In all these cases, the goal is to produce a soft magnetic composite with discontinuous, separated soft magnetic particles joined by a continuous electrical insulating medium. The DC magnetic properties (coercive field and maximum permeability) of the produced composite are far inferior to those of the main wrought soft magnetic constituting material in the form of lamination, and thus, hysteresis losses in an AC magnetic field are higher and the electrical current or the number of turns of copper wire required to reach the same torque must be higher. Properties of those composites are well suited for applications frequency above 10 KHz to 1 MHz. If power frequencies are targeted (US Patents EP 0 088 992 A2 and WO 02/058865), the design of the component must compensate for the lower permeability and higher hysteresis losses of the material. Finally, some people who have discovered the benefit of using lamellar particles for doing soft magnetic components have developed coating able to sustain annealing temperature, that is to say temperatures which are high enough to remove the major part of the remaining strain in the parts (US Patents 3,255,052; 3,848,331; 4,158,580; 4,158,582; 4,265,681). Once again, magnetic properties and energetic losses in an AC magnetic field at frequencies under 400Hz are not those reached with good lamination steel or silicon steel used commercially, since metallic diffusion between soft magnetic particles is avoided to keep high electrical resistivity in the composite. Since all the actual soft magnetic composite are discontinuous metallic media, the mechanical strength of the material is limited to the strength of the insulating coating. When the material breaks, it is de-cohesion that occurs between metallic particles, in the organic or inorganic (vitrous/ceramic) coating. The mechanical behavior of the SMC is thus fragile with no possibility of plastic deformation and the strength is always far lower than that of metallurgically bonded materials. It is an important limitation of the SMC. Also known in the prior art are the sintered iron non coated powder components currently used to make parts for DC magnetic applications. These sintered parts have low resistivity and are generally not used in AC applications. In the literature or patents, when sintering treatments (metal to metal) or metallic diffusion are involved, soft magnetic parts produced are for DC applications where eddy currents are not a concern (US Patents 4,158,581; 5,594,186; 5,925,836; 6,117,205 for example) or for non-magnetic applications like structural parts. SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic composite for AC application, having improved magnetic properties (i.e. lower hysteresis and eddy current losses). In accordance with the present invention, this object is achieved with a magnetic composite for AC applications, comprising a consolidation of magnetizable metallic microlamellar particles each having top and bottom surfaces and opposite ends. The top and bottom surfaces are coated with a dielectric coating for increasing the resistivity of the composite and reducing eddy current losses. The composite is characterized in that the coating is made of a refractory material and the ends of the lamellar particles are metallurgically bonded to each other to reduce hysteresis losses of the composite. By metallurgically bonded, it is meant a metallic joint involving a metallic diffusion between the particles, obtained by sintering or forging or any other process allowing a metallic diffusion between the particles. In accordance with a first preferred embodiment, the metallurgically bonded ends are obtained by heating the consolidation of particles to a temperature of at least 800°C, more preferably, above 1000°C. In accordance with a second preferred embodiment, the metallurgically bonded ends are obtained by forging the consolidation. By refractory material, it is meant a material capable of withstanding the effects of high temperature. Preferably, the coating is made of a material stable at a temperature of at least 1000°C. The magnetic composite is preferably a soft magnetic composite having a coercive force of less than 500 A/m. In order to increase the resistivity of the composite, and thus reduce its eddy current losses when it is under the effect of an alternating magnetic field, the coating is also dielectric. Since the dielectric material is a refractory, it prevents formation of metallic contacts (metallurgic bonds) between each top and bottom surfaces of particles during the thermal treatment and keep a certain electrical insulation. In that sense, this refractory material acts as a diffusion barrier for each top and bottom surfaces of particles. The sintering or metallurgical bonding is thus preferential. The diffusion barrier or coating could be, for example, but it is not limited to, a metal oxide like silicon, titanium, aluminum, magnesium, zirconium, chromium, boron oxide and their combinations and all other oxides stable at a temperature above 1000°C under a reducing atmosphere, of a thickness between 0.01 urn to 10 urn, more preferably between 0.05pm and 2pm. The microlamellar particles are preferably made of a metallic material containing at least one of Fe, Ni and CO. More preferably, they are made of a material selected from the group consisting of pure iron, iron alloys, pure nickel, nickel alloys, iron-nickel alloys, pure cobalt, cobalt alloys, iron-cobalt alloys and iron-nickel-cobalt alloys. Also preferably, the microlamellar particles have a thickness (e) in the range of 15 to 150 rn, and have a length-to-thickness ratio greater than 3 and lower than 200. The magnetic composite according to the invention preferably has an energy loss when tested according to the ASTM standard A-773, A-927 for a toroid of at least 4 mm thickness in an AC electromagnetic field of 1 Tesla and a frequency of 60 Hz of less than 2W/kg. Also preferably, the magnetic composite shows the following magnetic and mechanical properties: - a coercive force of less than 100 A/m, preferably less than 50 A/m, and more preferably less than 25 A/m; a DC magnetic permeability of at least 1000, preferably at least 2500, and more preferably at least 5000; a transverse rupture strength of at least 125 MPa, preferably at least 500 MPa; and a plastic deformation zone like during mechanical testing (due to slow delamination of particles). The present invention is also directed to a process of manufacturing a magnetic composite comprising the steps of: a) providing microlamellar particles made of a magnetizable metallic material, the particles having opposite ends and a top and bottom surfaces, the top and bottom surfaces being coated with a dielectric and refractory coating; b) compacting the microlamellar particles into a predetermined shape for obtaining a consolidation of the microlamellar particles; and c) metallurgically bonding the ends of the microlamellar particles to each other. Preferably, step c) of metallurgically bonding comprises the step of: heating the consolidation at a temperature sufficient to sinter the ends of the microlamellar particles. The temperature sufficient to sinter is preferably at least 800°C; more preferably it is at least 1000°C. Alternatively, step c) of metallurgically bonding comprises the step of: forging the consolidation. The microlamellar particles are preferably obtained by: a1) providing a foil of the magnetizable material having a thickness of less than about 150um, the foil having a top and bottom surface coated with the dielectric and refractory coating; and a2) cutting the microlamellar particles from the foil. The diffusion barrier or coating material on the top and bottom surfaces of the microlamellar particles is obtained by a coating process adapted to produce a coating having a thickness of less than 10um. Preferably, it is made by a deposition technique (a physical vapor deposition (PVD) or chemical vapor deposition (CVD) process, plasma enhanced or not, or by dipping or spraying using a process such as the sol-gel process or the thermal decomposition of an oxide precursor, a surface reaction process (oxidation, phosphatation, salt bath reaction) or a combination of both (dipping the foil or particles into a liquid aluminum or magnesium bath, the CVD, PVD, Magnetron sputtering process of a pure metal coating and a chemical or thermo-chemical treatment to oxidize the coating formed during an additional step). BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Other objects and advantages of the invention will become apparent upon reading the following general and detailed description and upon referring to the drawings in which: Figure 1a is a SEM analysis of a transverse cut (plane by where the lines of any field are normally crossing through to obtain optimal magnetic properties) of a sintered flaky (or microlamellar) soft magnetic composite according to a first preferred embodiment of the invention, showing typical microstructure of the flaky (microlamellar) material. Figure 1b is a SEM analysis of a transverse cut of a forged magnetic composite according to a second preferred embodiment of the invention, shown at higher magnitude to see partial metallic diffusion between particles during sintering. Figures 2 and 3 are graphics showing the magnetic properties of a soft magnetic composite according to the invention compared with prior art magnetic materials; and Figure 4 is a schematic representation of the microstructure of a soft magnetic composite according to the first preferred embodiment of the invention. DESCRIPTION OF THE INVENTION Referring to figures 1a, 1b, or figure 4 which shows a typical stator (2) for an AC application that could be made with the composite of the invention, a magnetic composite (10) according to the invention consists of a consolidation of magnetizable metallic microlamellar particles (12) each having a top and bottom surfaces and opposite ends (14). The top and bottom surfaces are coated with a dielectric coating (16) for increasing the resistivity of the composite (10) and reducing eddy current losses. The composite (10) is characterized in that the coating (16) is made of a refractory material and the lamellar particles (12) are metallurgically bonded by their ends (14) to reduce hysteresis losses of the composite (10). The present invention covers the production process and the material that takes profit of the best properties of the two already existing technologies (i.e. lamination stacking and soft magnetic composite). The material produced with this technology can be fully sintered or forged to achieve good mechanical properties and excellent AC soft magnetic properties at frequencies comprised between 1 and 10 000Hz. In order to reduce hysteresis losses of the final part, and thus helping to reduce low frequency total losses of the part, the lamellar particles have their ends sintered, or metallurgically bonded, to each other. Losses at low frequencies are as low as for a lamination stacking. Losses at higher-frequencies are also low since eddy currents are limited by the use of very thin lamellar particles (0.0005 to 0.002" or 12.5 to 50 n). Even if electrical insulation is not total between particles, eddy currents are limited to only two or three layers of particles at zone with poor insulations (edges of particles) since, statistically, insulation defects are rarely aligned and are not aligned for more than few layers. The result is a composite material with total losses at frequencies varying between 0 and 400 Hz that are similar to those of a lamination stack made with the best grades of silicon steel (3.5 W/kg at 60 Hz 1.5T). Mechanical properties of this composite, when forged, are well above all composites previously developed with Transverse Rupture Strength1 values of 125 000 psi (875 MPa) without plastic deformation followed by a deformation zone (de-lamination) with a stable resistance of 65 000 psi (450 MPa). A composite according to the invention, when only sintered on a reducing atmosphere rather than forged, has TRS value in the same range as that of the best mechanically resistant soft magnetic composite containing a reticulated (cured) resin (18 000 psi, 125 MPa) (Gelinas, C. et al. "Effect of curing conditions on properties of iron-resin materials for low frequency AC magnetic applications", Metal Powder Industries Federation, Advances in Powder Metallurgy & Particulate Materials - 1998; Volume 2, Parts 5-9 (USA), pp. 8.3-8.11, June 1999). Contrary to previous soft magnetic composites developed, which all have a fragile comportment without any plastic deformation before complete rupture, the sintered or forged composite of the present invention shows a plastic deformation zone like or ductile comportment during mechanical testing. This comportment is due to a slow de-lamination of the composite. 1 Standard Test Methods, for Metal Powders and Powder Metallurgy Products, MPIF, Princeton, NJ, 1999(MPIF standard # 41, Metal Powders Industries Federation, 105 College Road East, Princeton, N. J. 08540-6692 U.S.A) Extra design liberty given by the process used to make a composite according to the invention (powder metallurgy allows design in three dimensions, lamination stacking is limited in a plane) allows to decrease the total losses of an electromagnetic device made with the composite of the invention (including copper losses) compared to losses generated by the same component made with a lamination stack. Volume and weight can also be decreased importantly with the composite of the invention. As the frequency of the application increases (above 500 Hz), conventional soft magnetic components made with irregular particles, or thin microlamellar particles fully insulated from each other and not sintered, can develop lower total losses due to their better limitation of eddy current losses even if hysteresis losses are higher due to distributed air gap. DETAILED DESCRIPTION OF A PREFERRED MODE OF REALIZATION A composite for soft magnetic application (ex: transformers, stator and rotor of motors, generators, alternators, a field concentrator, a synchroresolver, etc..) in accordance with the invention is preferably realized by: • Using pure iron, iron nickel alloys (with nickel content varying from 20 to 85%) which may also contain up to 20% Cr, less than 5 % of Mo, less than 5 % of Mn; silicon iron with a minimal contain of 80% of iron and with silicon content between 0 and 10%, that may contain less than 10% of Mo, less than 10% of Mn and less than 10% of Cr; iron cobalt alloys with cobalt content varying from 0 to 100% and that may contain less than 10% of Mo, less than 10% of Mn, less than 10% of Cr, and less than 10% of silicon; or finally, Fe-Ni-Co alloys at all content of Ni and Co that may contain a maximum of 20% of other alloying elements. • Using the pre-cited materials (or alloys) in the form of foils of a thickness between 10m and 500m, preferably under 125pm, more preferably under 50m, coated one or both sides with a very thin electrical insulating inorganic, heat resistant oxide of a thickness between 0.01 rn to 2m like silicon, titanium, aluminum, magnesium, zirconium, chromium, boron oxide and their combinations and all other oxides stable over 1000°C under a reducing atmosphere. • The foil is obtained from a standard hot and cold rolling process starting or not from a strip casting process and including or not some normalizing or full annealing stages during rolling (semi processed electrical steel or silicon steel or fully processed electrical or silicon steel or all other alloys sub-mentioned by rolling) or obtained by casting alloys sub-mentioned on a cooled rotating wheel (melt spinning, planar flow casting, strip casting, melt drag) no matter the width produced. The semi-processed steel or silicon steel could be decarburized prior to receiving the coating or after. A grain coarsening treatment (secondary recristallisation) to achieve optimal magnetic properties could have also been done prior to coating when possible. • The coating is obtained directly by dipping the foil into a liquid aluminum or magnesium bath, by a physical vapor deposition (PVD) or chemical vapor deposition (CVD) process, plasma enhanced or not, or by dipping or spraying using a process such as the sol-gel process or any process, involving the thermal decomposition of an oxide precursor. The CVD, PVD, Magnetron sputtering process could give directly an oxide layer or could give a pure metal coating like with the dipping of the foil into a metal bath. The pure metal coating, in those cases, has to be oxidized during a subsequent process. • Doing a grain coarsening thermal treatment at high temperature under reducing atmosphere on the coated foil to optimize its magnetic properties if the starting foil was not magnetically optimal. • Cutting the pre-cited foil coated and thermally treated or thermally treated and coated in the form of lamellar particles or flakes. Dicing or slitting and cutting the coated thin foils could give those flakes. • An alternative process gives flakes directly from more spherical powders (produced by another way like water or gaz atomization) by hot or cold rolling the powders or by the melt drag process with a dented wheel (machined with a lot of small grooves) to extract flakes from the melted metal or from an atomization process like rotary electrode or disk where the melted particles hit a wall or a hammer before solidifying. Flakes could be made finally by cutting a ribbon coming from a machining process. In all those last cases, the coating is applied directly on the lamellar particles, rather than on the ribbons to be cut and all edges are coated. • Mixing 0.1 to 1% by weight of lubricant with the pre-cited coated lamellar powders or flakes to help the following pressing process. The lubricant could also be applied by any process directly on the foil prior to its cutting to produce lamellar particles. Filling at least one pre-filling die with the lamellar particles. The pre-filling die could be sited on a vibrating table during the filling. A magnetic field could also be applied during the filling to orientate the flakes. The pre- filling die could be separated in two or three heights. After a light pressing (0,1 MPa to 10 MPa ), only the third or the two thirds of the initial height of the pre-filling die could be conserved for the powder transfer to the production press. Such pre-pressing is to increase their apparent density, to help the orientation of the flakes perpendicular to the pressing axe and to accelerate subsequent filling of the die of the production press. Sometimes during the filling of the pre-filling operation or after, a pressure in the range of 0,1 MPa to 10MPa could be applied. • Transferring the powder from the pre-filling die (or one part of its initial height) to the pressing die with the help of a synchronized movement of the upper punch and the lower punch of the press. The upper punch pressure could come from an external temporary punch (the same as the one used for the pre-filling die light compression for example) rather than the punch of the production press. The movement of the lower punch is a common feature during the filling of the press and is commonly named "suction filling". • Pressing the part with the main press with the use of an increase of temperature or not. The consolidation process could be a cold, warm or hot uniaxial process or isostatic process (cold or hot). • Sintering the compacted part to allow the formation of metal to metal contacts. Mechanical and magnetic properties are appreciably increased during the sintering process at a temperature above 1000 °C for at least 5 minutes. An assembling of many different parts could be sintered to obtain a bigger or a more complex rigid part. • Alternatively, rather than sintering, compressed parts could be pre-heated to above 1000°C and forged to achieve near full density. An assembling Of many different parts could be forged simultaneously to give a rigid part. • Alternatively, a repressing could be done on sintered parts to increase density. • A final anneal or another sintering treatment (double press-double sinter process) could be done if a repressing step is done on the parts. • If additional machining operations are required, a final anneal could be done on the parts to obtain the optimum magnetic properties. • Final parts could be dipped into a liquid polymer or metal or alloy to increase their mechanical properties and avoid the detachment of some lamellar particles on the surface of the parts. Any surface treatment could also be done to modify the surface of the parts. • The final part pressed and sintered or forged could be submitted to the following treatments. Those following treatments are given as an example but possible treatments are not limited to those following examples. Final parts could be infiltrated with one or more metals and alloys during a subsequent heat treatment to increase their mechanical properties, wear and corrosion resistance. Parts could also be infiltrated by an organic material to improve mechanical, wear or chemical resistance. Final parts could also be thermal sprayed or be submitted to many other forms of surface treatment. The metallography of the product combined with its magnetic properties (relative permeability well above 1000) and mechanical properties (transverse rupture strength (MPIF standard 41)) over 18 000 psi (125 MPa) is specific. In fact, metallography of figure 1 clearly shows the flaky nature of the composite and the properties reported in table 1 below testify of its sintering or metallurgic bonds between particles. Furthermore, the properties of the part are not modified by heating it in a reducing atmosphere at 1000°C for 15 minutes, testifying that its mechanical resistance does not come from an organic reticulated resin like for the most mechanically resistant actual soft magnetic composite, and showing that its electrical resistivity, evaluated from the slope of the curve on the graph of its energetic losses as a function of the frequency varying from 10 to 250 Hz in a field of 1 or 1.5 Tesla (figures 2 and 3), is conserved (low eddy current losses) even after a reducing treatment and a beginning of sintering contrarily of all other soft magnetic composites. Figures 1a and 1b show examples of the metallography of a sintered microlamellar or flaky soft magnetic composite according to two preferred embodiments of the invention (Sintered Flaky Soft magnetic composite SF- SMC). Table 1 and figures 2 and 3 show typical magnetic properties of the sintered flaky soft magnetic composite. EXAMPLES: The following properties and energetic losses (Figures 1 and 2 and table 1) were measured on standard toroid specimens of 6 mm (sintered) and 4 mm (forged) thickness for the SF-SMC and results are compared to some common laminations (silicon steel 0.35 mm thick laminations, electrical steel 0.6 mm thick laminations) or soft magnetic composites (SMC and Krause for patent 4,265,681) of approximately the same thickness. The new material is identified as "SF-SMC" (Sintered Flaky-Soft Magnetic Composite) Example 1: The process used to do the rings for which results are reported on table 1 (SF-SMC FeNi sintered) and figure 2 at an induction of 1.0 Tesla is the following: o Coating one side of a 50 n thick Fe-47.5% Ni foil with 0.4 urn of alumina in D.C. pulsed magnetron sputtering reactive process, • Annealing the ribbon during 4 hours at 1200°C under pure hydrogen, • Cutting the ribbon to form square lamellar particles of 2 mm by 2 mm sides, • Mixing the particles with 0.5 % acrawax in a "V" type mixer during 30 minutes, • Filling a plastic pre-filling die with the mixture, vibrating the pre-filling die during filling, pressing at 1 MPa, • Sliding the content of the pre-filling die into the steel die for cold pressing, pressing at 827 MPa and ejecting the compact, • Delubing the compact at 600 °C during 15 minutes, • Heating the compact at 1200°C under pure hydrogen during 30 minutes, and • Cooling the compact at 20 °C/min. A part of the same dimensions made with uncoated powders gave 5 times the losses at 60Hz and 6 times the losses at 260Hz. Example 2: The process used to do the rings which results are reported in table 1 (SF-SMC FeNi forged) on figure 3 at an induction of 1.5 Tesla is the following: • Coating one side of a 50 urn thick Fe-47.5% Ni foil with 0.4 urn of alumina in D.C. pulsed magnetron sputtering reactive process, • Annealing the ribbon during 4 hours at 1200°C under pure hydrogen, • Cutting the ribbon to form square lamellar particles of 2 mm by 2 mm sides, • Mixing the particles with 0.5 % acrawax in a V type mixer during 30 minutes, • Filling a pre-filling die with the mixture, vibrating the pre-filling die during filling, pressing at 1 MPa, • Sliding the content of the pre-filling die into the die for cold pressing, pressing at 827 MPa and ejecting the compact, • Heating the compact at 1000°C in air during 3 minutes and forging it at 620 Mpa, • Annealing the compact at 800°C during 30 minutes under pure hydrogen. A part of the same dimensions made with uncoated laminations gave 6 times the losses at 60 Hz and 8 times the losses at 260 Hz. Example 3: The process used to do the rings which results are reported on Table 1 (SF-SMC Fe-3%Si sintered) is the following: • Ribbons of iron containing 3% of silicon are produced by the technology of Planar Flow Casting (The melt product is directly poured on a high speed rotating wheel). • The 50 m thick ribbon is coated with a spray of a Sol-Gel solution made with aluminum isopropoxyde and dried by reaching 150°C in a continuous process. • The coated ribbon is annealed under pure hydrogen at 1200 °C during 2 hours and cooled to room temperature slowly. • The ribbons are sprayed another time with the Sol-Gel process. • The ribbons are then sprayed with EBS using an electrostatic charging system and cut into 2 mm by 2 mm square particles. • Particles are poured in a plastic pre-compacting die and pre-compacted at 150 lb per square inch (1 MPa). • The pre-compacted particles are transferred to a steel die (powder metallurgy compacting press) and cold pressed at 60 tons per square inch (827 Mpa) of compacting pressure. Compact is ejected. • The compact is then sintered in a conventional sintering furnace including a delubbing zone, a high temperature zone at 1120°C and a cooling zone. The time at 1120°C is approximately 10 minutes. The part is cooled approximately at 20°C/min. Exemple 4: The process used to do the rings which results are reported on Table 1 (SF-SMC Fe-3%Si forged) is the following: • Ribbons of iron containing 3% of silicon are produced by the technology of Planar Flow Casting (The melt product is directly poured on a high speed rotating wheel). • The 50 m thick ribbon is coated with a spray of a Sol-Gel solution made with aluminum isopropoxyde and dried by reaching 150°C in a continuous process. • The coated ribbon is annealed under pure hydrogen at 1200 °C during 2 hours and cooled to room temperature slowly. • The ribbons are sprayed another time with the Sol-Gel process. • The ribbons are then sprayed with EBS using an electrostatic charging system and cut into 2 mm by 2 mm square particles. • Particles are poured in a plastic pre-compacting die and pre-compacted at 150 lb per square inch (1 MPa). • The pre-compacted particles are transferred to a steel die (powder metallurgy compacting press) and cold pressed at 60 tons per square inch (827 Mpa) of compacting pressure. Compact is ejected. • Heating the compact at 1000°C in air during 3 minutes and forging it at 620 MPa. • Annealing the compact at 800°C during 30 minutes under pure hydrogen. Although the present invention has been explained hereinabove by way of a preferred embodiment thereof, it should be understood that the invention is not limited to this precise embodiment and that various changes and modifications may be effected therein without departing from the scope or spirit of the invention. WE CLAIM : 1. A magnetic composite for AC applications, comprising: a consolidation of magnetizable metallic microlamellar particles each having top and bottom surfaces and opposite ends, said top and bottom surfaces being coated with a dielectric coating for increasing the resistivity of the composite and reducing eddy current losses, characterized in that said coating is made of a refractory material and said ends of the lamellar particles are metallurgically bonded to each other yo reduce hysteresis losses of the composite. 2. A magnetic composite as claimed in claim 1, wherein it is a soft magnetic composite having a coercive force of less than 500 A/m. 3. A magnetic composite as claimed in claim 1 or 2, wherein said coating is made of a material stable at a temberature of at least 1000 °C. 4. A magnetic composite as claims 1 to 3, wherein said coating is made of at least one metal oxide. 5. A magnetic composite as claimed in claim 4, wherein said at least one metal oxide is selected from the group consisting of silicon, titanium, aluminum, magnesium, zirconium, chromium and boron oxide. 6. A magnetic composite as claimed in any one of claims 1 to 5, wherein said coating has a thickness in the range of 10 urn or less. 7. A magnetic composite as claimed in any one of claims 1 to 6, wherein the microlamellar particles are made of a metallic material containing at least one of Fe, Ni and Co. 8. A magnetic composite as claimed in any one of claims 1 to 7, wherein the microlamellar particles are made of a material selected from the group consisting of pure iron, iron alloys, pure nickel, nickel alloys, iron-nickel alloys, pure cobalt, cobalt alloys, iron-cobalt alloys and iron-nickel-cobalt alloys. 9. A magnetic composite as claimed in any one of claims 1 to 8, wherein said microlamellar particles have a thickness (e) in the range of 15 to 150 m. 10. A magnetic composite as claimed in any one of claims 1 to 9, wherein said microlamellar particles have a length to thickness ratio greater than 3 and lower than 200. 11. A magnetic composite as claimed in any one of claims 1 to 10, wherein the metallurgically bonded ends are obtained by heating said consolidation of particles to a temperature of at least 800 °C. 12. A magnetic composite as claimed in any one of claims 1 to 11, wherein the metallurgically bonded ends are obtained by heating said consolidation of particles to a temperature above 1000 °C. 13. A magnetic composite as claimed in any one of claims 1 to 10, wherein the metallurgically bonded ends are obtained by forging said consolidation. 14. A magnetic composite as claimed in any one of claims 1 to 13, wherein it has an energy loss when tested according to the ASTM standard A773, A927 for a toro'i'd of at least 4 mm thickness in an AC electromagnetic field of 1 Tesla and a frequency of 60 Hz of less than 2 W/kg. 15. A magnetic composite as claimed in any one of claims 1 to 14, wherein it has a coercive fore of less than 100 A/m. 16. A magnetic composite as claimed in any one of claims 1 to 15, wherein it has a coercive fore of less than 50 A/m. 17. A magnetic composite as claimed in any one of claims 1 to 16, wherein it has a coercive fore of less than 25 A/m. 18. A magnetic composite as claimed in any one of claims 1 to 17, wherein it has a DC magnetic permeability of at least 1000. 19. A magnetic composite as claimed in any one of claims 1 to 18, wherein it has a DC magnetic permeability of at least 2500. 20. A magnetic composite as claimed in any one of claims 1 to 19, wherein it has a DC magnetic permeability of at least 5000. 21. A magnetic composite as claimed in any one of claims 1 to 20, wherein it has a transverse rupture strength of at least 125 MPa. 22. A magnetic composite as claimed in any one of claims 1 to 21, wherein it has a transverse rupture strength of at least 500 MPa. 23. A magnetic composite as claimed in any one of claims 1 to 22, wherein it shows a plastic deformation zone during mechanical testing. 24. A process of manufacturing a magnetic composite comprising the steps of: (a) providing microlamellar particles made of a magnetizable metallic material, said particles having opposite ends and a top and bottom surfaces, said top and bottom surfaces being coated with a dielectric and refractory coating; (b) compacting said microlamellar particles into a predetermined shape for obtaining a consolidation of said microlamellar particles; and (c) metallurgically bonding the ends of said microlamellar particles to each other. 25. A process as claimed in claim 24, wherein step (c) of metallurgical^ bonding comprises the step of: - heating said consolidation at a temperature sufficient to sinter said ends. 26. A process as claimed in claim 25, wherein the temperature sufficient to sinter is at least 800 °C. 27. A process as claimed in claim 25, wherein the temperature sufficient to sinter is at least 1000 °C. 28. A process as claimed in claim 24, wherein step (c) of metallurgically bonding comprises the step of forging said consolidation. 29. A process as claimed in any one of claims 24 to 28, wherein step (a) comprises the steps of: (a1) providing a foil of said magnetizable material having a thickness of less than about 150 m, said foil having a top and bottom surfaces coated with said dielectric and refractory coating; and (a2) cutting said microlamellar particles from said foil. 30. A process as claimed in claim 29, wherein it comprises, prior to step (a1) of providing a foil, the step of coating said top and bottom surfaces of the foil, said coating step being selected from the following group consisting of a physical vapor deposition, a chemical vapor deposition, plasma deposition, a thermal decomposition of a dip or spray deposited oxide precursor and a surface reaction process so as to obtain a coating having a thickness of less than 2 m. 31. A process as claimed in any one of claims 29 or 30, wherein it comprises the step of thermally treating the foil to relieve stresses and coarsen grains of the foil. 32. A process as claimed in any one of claims 24 to 31, wherein step (b) of compacting is selected from the group consisting of uniaxial pressing, and cold or hot isostatic pressing. 33. A process as claimed in claim 32, wherein step (b) of compacting consists of uniaxial pressing comprising the steps of: (b1) filling the pressing die with said particles; and (b2) pressing said particles to obtain said consolidation of particles. 34. A process as claimed in claim 33, wherein it comprises, prior to step (b1) of filling, the steps of: filling a pre-filling die with said particles; pre-pressing said particles to increase the density of the mass; and transferring the pre-pressed particles to the pressing die of step (b1). 35. A process as claimed in claim 34, wherein it comprises, prior to the pre-filling step, the step of lubricating the particles and/or the die cavity. 36. A process as claimed in claim 34 or 35, wherein a pressure in the range of 0.1 MPa to 10 MPa is applied for the pre-pressing step. 37. A process as claimed in any one of claims 33 to 36, wherein a pressure in the range of 300 MPa to 1000 MPa is applied in step (b2) of pressing. 38. A magnetic composite obtained by a process as claimed in any one of claims 24 to 37. 39. A soft magnetic part having a magnetic composite as claimed in any one of claims 1 to 23. 40. A soft magnetic part as claimed in claim 39, wherein the soft magnetic part is selected from the group consisting of transformers, stator and rotor of motors, generator, alternators, field concentrators, chokes, relays, electromechanical actuators and synchroresolvers. A magnetic composite for AC applications with improved magnetic properties (i.e. low hysteresis losses and low eddy current losses) is disclosed. The composite comprises a consolidation of magnetizable metallic microlamellar particles each having a top ad bottom surfaces and opposite ends. The top and bottom surfaces are coated with a dielectric coating for increasing the resistivity of the composite and reducing eddy current losses. The dielectric coating is made of a refractory material and the ends of the lamellar particles are metallurgically bonded to each other to reduce hysteresis losses of the composite. A process for manufacturing the same is also disclosed. The composite is suitable for manufacturing devices for AC applications such as transformers, stator and rotor of motors, generators, alternators, field concentrators, chokes, relays, electromechanical actuators, synchroresolvers, etc.

Full Text

A MAGNETIC COMPOSITE FOR AC APPLICATIONS
AND A PROCESS FOR MANUFACTURING THE SAME
FIELD OF THE INVENTION
The present invention relates generally to the field of magnetic materials, more
specifically to soft or temporary magnetic composites for AC applications and to
the production of the same. More particularly, it concerns a soft magnetic
composite with reduced hysteresis and eddy current losses and very good
mechanical properties. The magnetic composite of the invention is well suited for
manufacturing power application devices such as stator or rotor of machines or
parts of relays operating at frequencies up to 10 000 Hz; or chokes, inductors or
transformers for frequencies up to 10 000 Hz.
BACKGROUND OF THE INVENTION
Magnetic materials can be divided into two major classes: permanent magnetic
materials (also referred to as hard magnetic materials) and temporary magnetic
materials (also referred to as soft magnetic materials).
The permanent magnets are characterized by a large remanence, so that after
removal of a magnetizing force, a high flux density remains. The permanent
magnets tend toward large hysteresis loops, which are the closed curves
showing the variation of the magnetic induction of a magnetic material with the
external magnetic field producing it when this field is changed through a
complete cycle. Permanent magnets are commonly physically hard substances
and are, therefore, called hard magnets.
The temporary or soft magnets have low values of remanence and small
hysteresis loops. They are commonly physically softer than the hard magnets

and are known as soft magnets. Ideally, the soft magnets should have large
values of permeability () up to a high saturated flux density. The value of the
permeability () is the ratio B/H, where H represents the applied magnetic field,
or magnetic force, expressed in amperes per meter (A/M) and B is the magnetic
flux density induced in the material, and it is expressed in teslas (one tesla being
equal to one weber per meter square (W/m2)).
Soft magnetic materials are usually for applications where they have to canalize
a varying magnetic flux. They are conventionally used for manufacturing
transformers, inductance for electronic circuits, magnetic screens, stator and
rotor of motors, generators, alternators, field concentrators, synchroresolver, etc.
A soft magnetic material has to rapidly react to the small variations of an external
inducing magnetic field, and that, without heating and without affecting the
frequency of the external field.
Therefore, soft magnets are usually used with alternating currents, and for
maximum efficiency, it is essential to minimize the energy losses associated with
the changing electric field. The energy losses, or core losses, as they are
sometimes called, result in conversion of electric energy to thermal energy. The
losses are usually expressed in terms of watts/kg (W/kg) for a given flux density
(in teslas) at a given frequency (in Hertz). There are two principal mechanisms by
which energy or core losses occur. These are hysteresis losses and eddy current
losses. Soft magnetic materials have to have a small hysteresis loop (a small
coercive field Hc) and a high flux density (B) at saturation.
As well explained in US 6,548,012, hysteresis losses are due to the energy
dissipated by the wall domain movement and they are proportional to the
frequency. They are influenced by the chemical composition and the structure of
the material.

Eddy currents are induced when a magnetic field is exposed to an alternating
magnetic field. These currents which travel normal to the direction of the
magnetic flux lead to an energy loss through Joule (resistance) heating. Eddy
current losses are expected to vary with the square of the frequency, and
inversely with the resistivity. The relative importance of the eddy current losses
thus depends on the electrical resistivity of the material.
In prior art, soft magnetic parts for alternative current of low and medium
frequency applications (between 50 Hz and 50 000 Hz) have been produced
using basically two different technologies, each having their advantages and
limitations.
The first and widely used, since the end of the 19th century, consists of punching
and stacking steel laminations. This well-known process involves material loss
since scrap material is generated from notches and edges of the laminations
when stamping. This material loss could be very costly with some specific alloys.
This process also requires a default free roll of material of dimensions greater
than the dimensions of the part to be produced. The laminations have the final
geometry or a subdivision of the final geometry of the parts and can be coated
with an organic and/or inorganic insulating material. Every imperfection on the
laminations like edges burr decreases the stacking factor of the final part and
thus its maximum induction. Also, mass production of laminations prevents
design with rounded edges to help copper wire winding. Due to the planar nature
of the laminations, their use limits the design of devices with 2 dimensions
distribution of the magnetic field. Indeed, the field is limited to travel only in the
plane of the laminations.
The cost of the laminations is related to their thickness. To limit energy losses
generated by eddy currents, as the magnetic field frequency of the application
increases, laminations thickness must be decreased. This increases the rolling

cost of the material and decreases the stacking factor of the final part due to
imperfect surface finish of the laminations and burrs and the relative importance
of the insulating coating. Laminations are thus well suited but limited to low
frequency applications.
The second process for the production of soft magnetic parts for AC applications,
well-known since the beginning of the 20th century, is a variant of the mass
production powder metallurgy process where particles used are electrically
isolated from each other by a coating (US Patents 421,067; 1,669,649;
1,789,477; 1,850,181; 1,859,067; 1,878,589; 2,330,590; 2,783,208; 4,543,208;
5,063,011; 5,211,896). To prevent the formation of electrical contacts between
the powder particles, and thus to reduce the eddy current losses, the powder
particles are not sintered for AC applications. Parts issued from this process are
commonly named "soft magnetic composites or SMC". Obviously, this process
has the advantage of eliminating material loss.
SMC are isotropic and thus offer the possibility of designing components which
allow the magnetic fields to move in the three dimensions. SMC allow also the
production of rounded edges with conventional powder metallurgy pressing
techniques. As mentioned above, those rounded edges help winding the electric
conductors. Due to the higher curvature radius of the rounded edges, the
electrical conductors require less insulation. Furthermore, a reduction in the
length of the conductors due to the rounded edges of the soft magnetic part is a
great advantage, since it allows the amount of copper used to be minimized as
well as the copper loss (loss due to the electrical resistivity of the electrical
conductor carrying the current in the electromagnetic device).
With rounded edges, the overall dimension of the electrical component could be
reduced, since electrical winding could be partially inlaid within the volume
normally occupied by the soft magnetic part. In addition, due to the isotropy of
t

the material and the gain of freedom of the pressing process, new designs that
increase total yield, decrease the volume or the weight for the same power
output of electric machines are possible, since a better distribution or movement
of the magnetic field in the three dimensions is possible.
Another advantage of the powder metallurgy process is the elimination of the
clamping mean needed to secure laminations together in the final part. With
laminations, clamping is sometimes replaced by a welding of the edges of
laminations. Using the later approach, the eddy currents are considerably
increased, and the total yield of the device or its frequency range application is
decreased.
The limitation of the SMC is their high hysteresis losses and low permeability
compared to steel laminations. Since particles must be insulated from each other
to limit eddy currents induction, there is a distributed air gap in the material that
decreases significantly the magnetic permeability and increases the coercive
field. Additionally, to prevent the destruction of the insulation or coating, SMC can
very hardly be fully annealed or achieve a complete recrystallisation with grain
coarsening. The temperatures reported for annealing SMC without loosing
insulation are about 600°C in a non-reducing atmosphere and with the use of
partially or totally inorganic coating (US Patents 2,230,228; 4,601,765;
4,602,957; 5,595,609; 5,754,936; 6,251,514; 6,331,270 B1; PCT/SE96/00397).
Although the annealing temperature commonly used is not sufficient to
completely remove residual strain in the particles or to cause recrystallisation or
grain growth, a substantial amelioration of the hysteresis losses is observed.
Ultimately, for all the soft magnetic composites with irregular or spherical
particles developed for AC applications until now, even if residual strain would
have been removed and grain growth would have been possible at temperatures
used for the annealing cycle of finished parts, metallic grain dimension is limited

to the size of the particles. This small grain size limits the possibility of increasing
the permeability, decreasing the coercive field or simply, the hysteresis losses in
the material. Indeed, the smaller the metallic grains are, the higher is the number
of grain boundaries, and more energy is required for moving the magnetic
domain walls and increasing the induction of the material in one direction.
Therefore, the resulting total energy losses (or core losses) of SMC parts at low
frequency (below 400Hz) is greater than the total energy losses obtained with
laminations. The low permeability values require also more copper wire to
achieve the same induction or torque in the electromagnetic device. An optimized
three dimensions and rounded winding edges design of the part made with the
SMC with irregular or spherical particles can partially or completely compensate
those higher hysteresis losses and low permeability values encountered with
SMC material at low frequency.
Some attempts have been made to develop more performing inorganic coatings
and processes for conventional soft magnetic composites that would allow a full
annealing of compacts and even recrystallisation without losing too much
electrical insulation between particles (US Patents 2,937,964; 5,352,522;
EP 0 088 992 A2; WO 02/058865). These prior art documents teach a heat
treatment at around 1000°C or less to consolidate particles by the diffusion or
interaction of the insulating material of each particle. In all these cases, the goal
is to produce a soft magnetic composite with discontinuous, separated soft
magnetic particles joined by a continuous electrical insulating medium. The DC
magnetic properties (coercive field and maximum permeability) of the produced
composite are far inferior to those of the main wrought soft magnetic constituting
material in the form of lamination, and thus, hysteresis losses in an AC magnetic
field are higher and the electrical current or the number of turns of copper wire
required to reach the same torque must be higher. Properties of those
composites are well suited for applications frequency above 10 KHz to 1 MHz. If
power frequencies are targeted (US Patents EP 0 088 992 A2 and

WO 02/058865), the design of the component must compensate for the lower
permeability and higher hysteresis losses of the material.
Finally, some people who have discovered the benefit of using lamellar particles
for doing soft magnetic components have developed coating able to sustain
annealing temperature, that is to say temperatures which are high enough to
remove the major part of the remaining strain in the parts (US Patents 3,255,052;
3,848,331; 4,158,580; 4,158,582; 4,265,681). Once again, magnetic properties
and energetic losses in an AC magnetic field at frequencies under 400Hz are not
those reached with good lamination steel or silicon steel used commercially,
since metallic diffusion between soft magnetic particles is avoided to keep high
electrical resistivity in the composite.
Since all the actual soft magnetic composite are discontinuous metallic media,
the mechanical strength of the material is limited to the strength of the insulating
coating. When the material breaks, it is de-cohesion that occurs between metallic
particles, in the organic or inorganic (vitrous/ceramic) coating. The mechanical
behavior of the SMC is thus fragile with no possibility of plastic deformation and
the strength is always far lower than that of metallurgically bonded materials. It is
an important limitation of the SMC.
Also known in the prior art are the sintered iron non coated powder components
currently used to make parts for DC magnetic applications. These sintered parts
have low resistivity and are generally not used in AC applications. In the literature
or patents, when sintering treatments (metal to metal) or metallic diffusion are
involved, soft magnetic parts produced are for DC applications where eddy
currents are not a concern (US Patents 4,158,581; 5,594,186; 5,925,836;
6,117,205 for example) or for non-magnetic applications like structural parts.

SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic composite for AC
application, having improved magnetic properties (i.e. lower hysteresis and eddy
current losses).
In accordance with the present invention, this object is achieved with a magnetic
composite for AC applications, comprising a consolidation of magnetizable
metallic microlamellar particles each having top and bottom surfaces and
opposite ends. The top and bottom surfaces are coated with a dielectric coating
for increasing the resistivity of the composite and reducing eddy current losses.
The composite is characterized in that the coating is made of a refractory
material and the ends of the lamellar particles are metallurgically bonded to each
other to reduce hysteresis losses of the composite.
By metallurgically bonded, it is meant a metallic joint involving a metallic diffusion
between the particles, obtained by sintering or forging or any other process
allowing a metallic diffusion between the particles. In accordance with a first
preferred embodiment, the metallurgically bonded ends are obtained by heating
the consolidation of particles to a temperature of at least 800°C, more preferably,
above 1000°C. In accordance with a second preferred embodiment, the
metallurgically bonded ends are obtained by forging the consolidation.
By refractory material, it is meant a material capable of withstanding the effects
of high temperature. Preferably, the coating is made of a material stable at a
temperature of at least 1000°C.
The magnetic composite is preferably a soft magnetic composite having a
coercive force of less than 500 A/m.
In order to increase the resistivity of the composite, and thus reduce its eddy
current losses when it is under the effect of an alternating magnetic field, the

coating is also dielectric. Since the dielectric material is a refractory, it prevents
formation of metallic contacts (metallurgic bonds) between each top and bottom
surfaces of particles during the thermal treatment and keep a certain electrical
insulation. In that sense, this refractory material acts as a diffusion barrier for
each top and bottom surfaces of particles. The sintering or metallurgical bonding
is thus preferential.
The diffusion barrier or coating could be, for example, but it is not limited to, a
metal oxide like silicon, titanium, aluminum, magnesium, zirconium, chromium,
boron oxide and their combinations and all other oxides stable at a temperature
above 1000°C under a reducing atmosphere, of a thickness between 0.01 urn to
10 urn, more preferably between 0.05pm and 2pm. The microlamellar particles
are preferably made of a metallic material containing at least one of Fe, Ni and
CO. More preferably, they are made of a material selected from the group
consisting of pure iron, iron alloys, pure nickel, nickel alloys, iron-nickel alloys,
pure cobalt, cobalt alloys, iron-cobalt alloys and iron-nickel-cobalt alloys. Also
preferably, the microlamellar particles have a thickness (e) in the range of 15 to
150 rn, and have a length-to-thickness ratio greater than 3 and lower than 200.
The magnetic composite according to the invention preferably has an energy loss
when tested according to the ASTM standard A-773, A-927 for a toroid of at least
4 mm thickness in an AC electromagnetic field of 1 Tesla and a frequency of 60
Hz of less than 2W/kg.
Also preferably, the magnetic composite shows the following magnetic and
mechanical properties:
- a coercive force of less than 100 A/m, preferably less than 50 A/m, and more
preferably less than 25 A/m;

a DC magnetic permeability of at least 1000, preferably at least 2500, and
more preferably at least 5000;
a transverse rupture strength of at least 125 MPa, preferably at least 500 MPa;
and
a plastic deformation zone like during mechanical testing (due to slow
delamination of particles).
The present invention is also directed to a process of manufacturing a magnetic
composite comprising the steps of:
a) providing microlamellar particles made of a magnetizable metallic
material, the particles having opposite ends and a top and bottom surfaces, the
top and bottom surfaces being coated with a dielectric and refractory coating;
b) compacting the microlamellar particles into a predetermined shape for
obtaining a consolidation of the microlamellar particles; and
c) metallurgically bonding the ends of the microlamellar particles to each
other.
Preferably, step c) of metallurgically bonding comprises the step of: heating the
consolidation at a temperature sufficient to sinter the ends of the microlamellar
particles.
The temperature sufficient to sinter is preferably at least 800°C; more preferably
it is at least 1000°C.
Alternatively, step c) of metallurgically bonding comprises the step of: forging the
consolidation.

The microlamellar particles are preferably obtained by:
a1) providing a foil of the magnetizable material having a thickness of less
than about 150um, the foil having a top and bottom surface coated with the
dielectric and refractory coating; and
a2) cutting the microlamellar particles from the foil.
The diffusion barrier or coating material on the top and bottom surfaces of the
microlamellar particles is obtained by a coating process adapted to produce a
coating having a thickness of less than 10um. Preferably, it is made by a
deposition technique (a physical vapor deposition (PVD) or chemical vapor
deposition (CVD) process, plasma enhanced or not, or by dipping or spraying
using a process such as the sol-gel process or the thermal decomposition of an
oxide precursor, a surface reaction process (oxidation, phosphatation, salt bath
reaction) or a combination of both (dipping the foil or particles into a liquid
aluminum or magnesium bath, the CVD, PVD, Magnetron sputtering process of a
pure metal coating and a chemical or thermo-chemical treatment to oxidize the
coating formed during an additional step).
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Other objects and advantages of the invention will become apparent upon
reading the following general and detailed description and upon referring to the
drawings in which:
Figure 1a is a SEM analysis of a transverse cut (plane by where the lines of any
field are normally crossing through to obtain optimal magnetic properties) of a
sintered flaky (or microlamellar) soft magnetic composite according to a first
preferred embodiment of the invention, showing typical microstructure of the flaky
(microlamellar) material.

Figure 1b is a SEM analysis of a transverse cut of a forged magnetic composite
according to a second preferred embodiment of the invention, shown at higher
magnitude to see partial metallic diffusion between particles during sintering.
Figures 2 and 3 are graphics showing the magnetic properties of a soft magnetic
composite according to the invention compared with prior art magnetic materials;
and
Figure 4 is a schematic representation of the microstructure of a soft magnetic
composite according to the first preferred embodiment of the invention.
DESCRIPTION OF THE INVENTION
Referring to figures 1a, 1b, or figure 4 which shows a typical stator (2) for an AC
application that could be made with the composite of the invention, a magnetic
composite (10) according to the invention consists of a consolidation of
magnetizable metallic microlamellar particles (12) each having a top and bottom
surfaces and opposite ends (14). The top and bottom surfaces are coated with a
dielectric coating (16) for increasing the resistivity of the composite (10) and
reducing eddy current losses. The composite (10) is characterized in that the
coating (16) is made of a refractory material and the lamellar particles (12) are
metallurgically bonded by their ends (14) to reduce hysteresis losses of the
composite (10).
The present invention covers the production process and the material that takes
profit of the best properties of the two already existing technologies (i.e.
lamination stacking and soft magnetic composite). The material produced with
this technology can be fully sintered or forged to achieve good mechanical
properties and excellent AC soft magnetic properties at frequencies comprised
between 1 and 10 000Hz. In order to reduce hysteresis losses of the final part,

and thus helping to reduce low frequency total losses of the part, the lamellar
particles have their ends sintered, or metallurgically bonded, to each other.
Losses at low frequencies are as low as for a lamination stacking. Losses at
higher-frequencies are also low since eddy currents are limited by the use of very
thin lamellar particles (0.0005 to 0.002" or 12.5 to 50 n). Even if electrical
insulation is not total between particles, eddy currents are limited to only two or
three layers of particles at zone with poor insulations (edges of particles) since,
statistically, insulation defects are rarely aligned and are not aligned for more
than few layers. The result is a composite material with total losses at
frequencies varying between 0 and 400 Hz that are similar to those of a
lamination stack made with the best grades of silicon steel (3.5 W/kg at 60 Hz
1.5T). Mechanical properties of this composite, when forged, are well above all
composites previously developed with Transverse Rupture Strength1 values of
125 000 psi (875 MPa) without plastic deformation followed by a deformation
zone (de-lamination) with a stable resistance of 65 000 psi (450 MPa). A
composite according to the invention, when only sintered on a reducing
atmosphere rather than forged, has TRS value in the same range as that of the
best mechanically resistant soft magnetic composite containing a reticulated
(cured) resin (18 000 psi, 125 MPa) (Gelinas, C. et al. "Effect of curing conditions
on properties of iron-resin materials for low frequency AC magnetic applications",
Metal Powder Industries Federation, Advances in Powder Metallurgy &
Particulate Materials - 1998; Volume 2, Parts 5-9 (USA), pp. 8.3-8.11, June
1999). Contrary to previous soft magnetic composites developed, which all have
a fragile comportment without any plastic deformation before complete rupture,
the sintered or forged composite of the present invention shows a plastic
deformation zone like or ductile comportment during mechanical testing. This
comportment is due to a slow de-lamination of the composite.
1 Standard Test Methods, for Metal Powders and Powder Metallurgy Products, MPIF, Princeton, NJ, 1999(MPIF standard
# 41, Metal Powders Industries Federation, 105 College Road East, Princeton, N. J. 08540-6692 U.S.A)

Extra design liberty given by the process used to make a composite according to
the invention (powder metallurgy allows design in three dimensions, lamination
stacking is limited in a plane) allows to decrease the total losses of an
electromagnetic device made with the composite of the invention (including
copper losses) compared to losses generated by the same component made
with a lamination stack. Volume and weight can also be decreased importantly
with the composite of the invention. As the frequency of the application increases
(above 500 Hz), conventional soft magnetic components made with irregular
particles, or thin microlamellar particles fully insulated from each other and not
sintered, can develop lower total losses due to their better limitation of eddy
current losses even if hysteresis losses are higher due to distributed air gap.
DETAILED DESCRIPTION OF A PREFERRED MODE OF REALIZATION
A composite for soft magnetic application (ex: transformers, stator and rotor of
motors, generators, alternators, a field concentrator, a synchroresolver, etc..) in
accordance with the invention is preferably realized by:
• Using pure iron, iron nickel alloys (with nickel content varying from 20 to
85%) which may also contain up to 20% Cr, less than 5 % of Mo, less than
5 % of Mn; silicon iron with a minimal contain of 80% of iron and with
silicon content between 0 and 10%, that may contain less than 10% of Mo,
less than 10% of Mn and less than 10% of Cr; iron cobalt alloys with
cobalt content varying from 0 to 100% and that may contain less than 10%
of Mo, less than 10% of Mn, less than 10% of Cr, and less than 10% of
silicon; or finally, Fe-Ni-Co alloys at all content of Ni and Co that may
contain a maximum of 20% of other alloying elements.
• Using the pre-cited materials (or alloys) in the form of foils of a thickness
between 10m and 500m, preferably under 125pm, more preferably

under 50m, coated one or both sides with a very thin electrical insulating
inorganic, heat resistant oxide of a thickness between 0.01 rn to 2m like
silicon, titanium, aluminum, magnesium, zirconium, chromium, boron
oxide and their combinations and all other oxides stable over 1000°C
under a reducing atmosphere.
• The foil is obtained from a standard hot and cold rolling process
starting or not from a strip casting process and including or not
some normalizing or full annealing stages during rolling (semi
processed electrical steel or silicon steel or fully processed
electrical or silicon steel or all other alloys sub-mentioned by rolling)
or obtained by casting alloys sub-mentioned on a cooled rotating
wheel (melt spinning, planar flow casting, strip casting, melt drag)
no matter the width produced. The semi-processed steel or silicon
steel could be decarburized prior to receiving the coating or after. A
grain coarsening treatment (secondary recristallisation) to achieve
optimal magnetic properties could have also been done prior to
coating when possible.
• The coating is obtained directly by dipping the foil into a liquid
aluminum or magnesium bath, by a physical vapor deposition
(PVD) or chemical vapor deposition (CVD) process, plasma
enhanced or not, or by dipping or spraying using a process such as
the sol-gel process or any process, involving the thermal
decomposition of an oxide precursor. The CVD, PVD, Magnetron
sputtering process could give directly an oxide layer or could give a
pure metal coating like with the dipping of the foil into a metal bath.
The pure metal coating, in those cases, has to be oxidized during a
subsequent process.

• Doing a grain coarsening thermal treatment at high temperature under
reducing atmosphere on the coated foil to optimize its magnetic properties
if the starting foil was not magnetically optimal.
• Cutting the pre-cited foil coated and thermally treated or thermally treated
and coated in the form of lamellar particles or flakes. Dicing or slitting and
cutting the coated thin foils could give those flakes.
• An alternative process gives flakes directly from more spherical powders
(produced by another way like water or gaz atomization) by hot or cold
rolling the powders or by the melt drag process with a dented wheel
(machined with a lot of small grooves) to extract flakes from the melted
metal or from an atomization process like rotary electrode or disk where
the melted particles hit a wall or a hammer before solidifying. Flakes could
be made finally by cutting a ribbon coming from a machining process. In
all those last cases, the coating is applied directly on the lamellar particles,
rather than on the ribbons to be cut and all edges are coated.
• Mixing 0.1 to 1% by weight of lubricant with the pre-cited coated lamellar
powders or flakes to help the following pressing process. The lubricant
could also be applied by any process directly on the foil prior to its cutting
to produce lamellar particles.
Filling at least one pre-filling die with the lamellar particles. The pre-filling
die could be sited on a vibrating table during the filling. A magnetic field
could also be applied during the filling to orientate the flakes. The pre-
filling die could be separated in two or three heights. After a light pressing
(0,1 MPa to 10 MPa ), only the third or the two thirds of the initial height of
the pre-filling die could be conserved for the powder transfer to the
production press. Such pre-pressing is to increase their apparent density,

to help the orientation of the flakes perpendicular to the pressing axe and
to accelerate subsequent filling of the die of the production press.
Sometimes during the filling of the pre-filling operation or after, a pressure
in the range of 0,1 MPa to 10MPa could be applied.
• Transferring the powder from the pre-filling die (or one part of its initial
height) to the pressing die with the help of a synchronized movement of
the upper punch and the lower punch of the press. The upper punch
pressure could come from an external temporary punch (the same as the
one used for the pre-filling die light compression for example) rather than
the punch of the production press. The movement of the lower punch is a
common feature during the filling of the press and is commonly named
"suction filling".
• Pressing the part with the main press with the use of an increase of
temperature or not. The consolidation process could be a cold, warm or
hot uniaxial process or isostatic process (cold or hot).
• Sintering the compacted part to allow the formation of metal to metal
contacts. Mechanical and magnetic properties are appreciably increased
during the sintering process at a temperature above 1000 °C for at least 5
minutes. An assembling of many different parts could be sintered to obtain
a bigger or a more complex rigid part.
• Alternatively, rather than sintering, compressed parts could be pre-heated
to above 1000°C and forged to achieve near full density. An assembling Of
many different parts could be forged simultaneously to give a rigid part.
• Alternatively, a repressing could be done on sintered parts to increase
density.

• A final anneal or another sintering treatment (double press-double sinter
process) could be done if a repressing step is done on the parts.
• If additional machining operations are required, a final anneal could be
done on the parts to obtain the optimum magnetic properties.
• Final parts could be dipped into a liquid polymer or metal or alloy to
increase their mechanical properties and avoid the detachment of some
lamellar particles on the surface of the parts. Any surface treatment could
also be done to modify the surface of the parts.
• The final part pressed and sintered or forged could be submitted to the
following treatments. Those following treatments are given as an example
but possible treatments are not limited to those following examples. Final
parts could be infiltrated with one or more metals and alloys during a
subsequent heat treatment to increase their mechanical properties, wear
and corrosion resistance. Parts could also be infiltrated by an organic
material to improve mechanical, wear or chemical resistance. Final parts
could also be thermal sprayed or be submitted to many other forms of
surface treatment.
The metallography of the product combined with its magnetic properties (relative
permeability well above 1000) and mechanical properties (transverse rupture
strength (MPIF standard 41)) over 18 000 psi (125 MPa) is specific. In fact,
metallography of figure 1 clearly shows the flaky nature of the composite and the
properties reported in table 1 below testify of its sintering or metallurgic bonds
between particles. Furthermore, the properties of the part are not modified by
heating it in a reducing atmosphere at 1000°C for 15 minutes, testifying that its
mechanical resistance does not come from an organic reticulated resin like for
the most mechanically resistant actual soft magnetic composite, and showing

that its electrical resistivity, evaluated from the slope of the curve on the graph of
its energetic losses as a function of the frequency varying from 10 to 250 Hz in a
field of 1 or 1.5 Tesla (figures 2 and 3), is conserved (low eddy current losses)
even after a reducing treatment and a beginning of sintering contrarily of all other
soft magnetic composites.
Figures 1a and 1b show examples of the metallography of a sintered
microlamellar or flaky soft magnetic composite according to two preferred
embodiments of the invention (Sintered Flaky Soft magnetic composite SF-
SMC). Table 1 and figures 2 and 3 show typical magnetic properties of the
sintered flaky soft magnetic composite.
EXAMPLES:
The following properties and energetic losses (Figures 1 and 2 and table 1)
were measured on standard toroid specimens of 6 mm (sintered) and 4 mm
(forged) thickness for the SF-SMC and results are compared to some
common laminations (silicon steel 0.35 mm thick laminations, electrical steel
0.6 mm thick laminations) or soft magnetic composites (SMC and Krause for
patent 4,265,681) of approximately the same thickness. The new material is
identified as "SF-SMC" (Sintered Flaky-Soft Magnetic Composite)
Example 1: The process used to do the rings for which results are reported on
table 1 (SF-SMC FeNi sintered) and figure 2 at an induction of 1.0 Tesla is the
following:
o Coating one side of a 50 n thick Fe-47.5% Ni foil with 0.4 urn of alumina
in D.C. pulsed magnetron sputtering reactive process,
• Annealing the ribbon during 4 hours at 1200°C under pure hydrogen,

• Cutting the ribbon to form square lamellar particles of 2 mm by 2 mm
sides,
• Mixing the particles with 0.5 % acrawax in a "V" type mixer during 30
minutes,
• Filling a plastic pre-filling die with the mixture, vibrating the pre-filling die
during filling, pressing at 1 MPa,
• Sliding the content of the pre-filling die into the steel die for cold pressing,
pressing at 827 MPa and ejecting the compact,
• Delubing the compact at 600 °C during 15 minutes,
• Heating the compact at 1200°C under pure hydrogen during 30 minutes,
and
• Cooling the compact at 20 °C/min.
A part of the same dimensions made with uncoated powders gave 5 times the
losses at 60Hz and 6 times the losses at 260Hz.
Example 2: The process used to do the rings which results are reported in table
1 (SF-SMC FeNi forged) on figure 3 at an induction of 1.5 Tesla is the following:
• Coating one side of a 50 urn thick Fe-47.5% Ni foil with 0.4 urn of alumina
in D.C. pulsed magnetron sputtering reactive process,
• Annealing the ribbon during 4 hours at 1200°C under pure hydrogen,

• Cutting the ribbon to form square lamellar particles of 2 mm by 2 mm
sides,
• Mixing the particles with 0.5 % acrawax in a V type mixer during 30
minutes,
• Filling a pre-filling die with the mixture, vibrating the pre-filling die during
filling, pressing at 1 MPa,
• Sliding the content of the pre-filling die into the die for cold pressing,
pressing at 827 MPa and ejecting the compact,
• Heating the compact at 1000°C in air during 3 minutes and forging it at
620 Mpa,
• Annealing the compact at 800°C during 30 minutes under pure hydrogen.
A part of the same dimensions made with uncoated laminations gave 6 times the
losses at 60 Hz and 8 times the losses at 260 Hz.
Example 3: The process used to do the rings which results are reported on
Table 1 (SF-SMC Fe-3%Si sintered) is the following:
• Ribbons of iron containing 3% of silicon are produced by the technology of
Planar Flow Casting (The melt product is directly poured on a high speed
rotating wheel).
• The 50 m thick ribbon is coated with a spray of a Sol-Gel solution made
with aluminum isopropoxyde and dried by reaching 150°C in a continuous
process.

• The coated ribbon is annealed under pure hydrogen at 1200 °C during
2 hours and cooled to room temperature slowly.
• The ribbons are sprayed another time with the Sol-Gel process.
• The ribbons are then sprayed with EBS using an electrostatic charging
system and cut into 2 mm by 2 mm square particles.
• Particles are poured in a plastic pre-compacting die and pre-compacted at
150 lb per square inch (1 MPa).
• The pre-compacted particles are transferred to a steel die (powder
metallurgy compacting press) and cold pressed at 60 tons per square inch
(827 Mpa) of compacting pressure. Compact is ejected.
• The compact is then sintered in a conventional sintering furnace including
a delubbing zone, a high temperature zone at 1120°C and a cooling zone.
The time at 1120°C is approximately 10 minutes. The part is cooled
approximately at 20°C/min.
Exemple 4: The process used to do the rings which results are reported on
Table 1 (SF-SMC Fe-3%Si forged) is the following:
• Ribbons of iron containing 3% of silicon are produced by the technology of
Planar Flow Casting (The melt product is directly poured on a high speed
rotating wheel).
• The 50 m thick ribbon is coated with a spray of a Sol-Gel solution made
with aluminum isopropoxyde and dried by reaching 150°C in a continuous
process.

• The coated ribbon is annealed under pure hydrogen at 1200 °C during
2 hours and cooled to room temperature slowly.
• The ribbons are sprayed another time with the Sol-Gel process.
• The ribbons are then sprayed with EBS using an electrostatic charging
system and cut into 2 mm by 2 mm square particles.
• Particles are poured in a plastic pre-compacting die and pre-compacted at
150 lb per square inch (1 MPa).
• The pre-compacted particles are transferred to a steel die (powder
metallurgy compacting press) and cold pressed at 60 tons per square inch
(827 Mpa) of compacting pressure. Compact is ejected.
• Heating the compact at 1000°C in air during 3 minutes and forging it at
620 MPa.
• Annealing the compact at 800°C during 30 minutes under pure hydrogen.

Although the present invention has been explained hereinabove by way of a
preferred embodiment thereof, it should be understood that the invention is not
limited to this precise embodiment and that various changes and modifications
may be effected therein without departing from the scope or spirit of the
invention.

WE CLAIM :
1. A magnetic composite for AC applications, comprising:
a consolidation of magnetizable metallic microlamellar particles each having
top and bottom surfaces and opposite ends, said top and bottom surfaces being
coated with a dielectric coating for increasing the resistivity of the composite and
reducing eddy current losses,
characterized in that
said coating is made of a refractory material and said ends of the lamellar
particles are metallurgically bonded to each other yo reduce hysteresis
losses of the composite.
2. A magnetic composite as claimed in claim 1, wherein it is a soft magnetic
composite having a coercive force of less than 500 A/m.
3. A magnetic composite as claimed in claim 1 or 2, wherein said coating is
made of a material stable at a temberature of at least 1000 °C.
4. A magnetic composite as claims 1 to 3, wherein said
coating is made of at least one metal oxide.
5. A magnetic composite as claimed in claim 4, wherein said at least one metal
oxide is selected from the group consisting of silicon, titanium, aluminum,
magnesium, zirconium, chromium and boron oxide.
6. A magnetic composite as claimed in any one of claims 1 to 5, wherein said
coating has a thickness in the range of 10 urn or less.
7. A magnetic composite as claimed in any one of claims 1 to 6, wherein the
microlamellar particles are made of a metallic material containing at least one of Fe,
Ni and Co.

8. A magnetic composite as claimed in any one of claims 1 to 7, wherein the
microlamellar particles are made of a material selected from the group consisting of
pure iron, iron alloys, pure nickel, nickel alloys, iron-nickel alloys, pure cobalt, cobalt
alloys, iron-cobalt alloys and iron-nickel-cobalt alloys.
9. A magnetic composite as claimed in any one of claims 1 to 8, wherein said
microlamellar particles have a thickness (e) in the range of 15 to 150 m.
10. A magnetic composite as claimed in any one of claims 1 to 9, wherein said
microlamellar particles have a length to thickness ratio greater than 3 and lower
than 200.
11. A magnetic composite as claimed in any one of claims 1 to 10, wherein the
metallurgically bonded ends are obtained by heating said consolidation of particles
to a temperature of at least 800 °C.
12. A magnetic composite as claimed in any one of claims 1 to 11, wherein the
metallurgically bonded ends are obtained by heating said consolidation of particles
to a temperature above 1000 °C.
13. A magnetic composite as claimed in any one of claims 1 to 10, wherein the
metallurgically bonded ends are obtained by forging said consolidation.
14. A magnetic composite as claimed in any one of claims 1 to 13, wherein it has
an energy loss when tested according to the ASTM standard A773, A927 for a
toro'i'd of at least 4 mm thickness in an AC electromagnetic field of 1 Tesla and a
frequency of 60 Hz of less than 2 W/kg.
15. A magnetic composite as claimed in any one of claims 1 to 14, wherein it has
a coercive fore of less than 100 A/m.

16. A magnetic composite as claimed in any one of claims 1 to 15, wherein it has
a coercive fore of less than 50 A/m.
17. A magnetic composite as claimed in any one of claims 1 to 16, wherein it has
a coercive fore of less than 25 A/m.
18. A magnetic composite as claimed in any one of claims 1 to 17, wherein it has
a DC magnetic permeability of at least 1000.
19. A magnetic composite as claimed in any one of claims 1 to 18, wherein it has
a DC magnetic permeability of at least 2500.
20. A magnetic composite as claimed in any one of claims 1 to 19, wherein it has
a DC magnetic permeability of at least 5000.
21. A magnetic composite as claimed in any one of claims 1 to 20, wherein it has
a transverse rupture strength of at least 125 MPa.
22. A magnetic composite as claimed in any one of claims 1 to 21, wherein it has
a transverse rupture strength of at least 500 MPa.
23. A magnetic composite as claimed in any one of claims 1 to 22, wherein it
shows a plastic deformation zone during mechanical testing.
24. A process of manufacturing a magnetic composite comprising the steps of:
(a) providing microlamellar particles made of a magnetizable metallic
material, said particles having opposite ends and a top and bottom surfaces, said
top and bottom surfaces being coated with a dielectric and refractory coating;
(b) compacting said microlamellar particles into a predetermined shape
for obtaining a consolidation of said microlamellar particles; and

(c) metallurgically bonding the ends of said microlamellar particles to each
other.
25. A process as claimed in claim 24, wherein step (c) of metallurgical^ bonding
comprises the step of:
- heating said consolidation at a temperature sufficient to sinter said ends.
26. A process as claimed in claim 25, wherein the temperature sufficient to sinter
is at least 800 °C.
27. A process as claimed in claim 25, wherein the temperature sufficient to sinter
is at least 1000 °C.
28. A process as claimed in claim 24, wherein step (c) of metallurgically bonding
comprises the step of forging said consolidation.
29. A process as claimed in any one of claims 24 to 28, wherein step (a)
comprises the steps of:
(a1) providing a foil of said magnetizable material having a thickness of
less than about 150 m, said foil having a top and bottom surfaces coated with said
dielectric and refractory coating; and
(a2) cutting said microlamellar particles from said foil.
30. A process as claimed in claim 29, wherein it comprises, prior to step (a1) of
providing a foil, the step of coating said top and bottom surfaces of the foil, said
coating step being selected from the following group consisting of a physical vapor
deposition, a chemical vapor deposition, plasma deposition, a thermal
decomposition of a dip or spray deposited oxide precursor and a surface reaction
process so as to obtain a coating having a thickness of less than 2 m.

31. A process as claimed in any one of claims 29 or 30, wherein it comprises the
step of thermally treating the foil to relieve stresses and coarsen grains of the foil.
32. A process as claimed in any one of claims 24 to 31, wherein step (b) of
compacting is selected from the group consisting of uniaxial pressing, and cold or
hot isostatic pressing.
33. A process as claimed in claim 32, wherein step (b) of compacting consists of
uniaxial pressing comprising the steps of:
(b1) filling the pressing die with said particles; and
(b2) pressing said particles to obtain said consolidation of particles.
34. A process as claimed in claim 33, wherein it comprises, prior to step (b1) of
filling, the steps of:
filling a pre-filling die with said particles;
pre-pressing said particles to increase the density of the mass; and
transferring the pre-pressed particles to the pressing die of step (b1).
35. A process as claimed in claim 34, wherein it comprises, prior to the pre-filling
step, the step of lubricating the particles and/or the die cavity.
36. A process as claimed in claim 34 or 35, wherein a pressure in the range of
0.1 MPa to 10 MPa is applied for the pre-pressing step.
37. A process as claimed in any one of claims 33 to 36, wherein a pressure in
the range of 300 MPa to 1000 MPa is applied in step (b2) of pressing.
38. A magnetic composite obtained by a process as claimed in any one of claims
24 to 37.

39. A soft magnetic part having a magnetic composite as claimed in any one of
claims 1 to 23.
40. A soft magnetic part as claimed in claim 39, wherein the soft magnetic part is
selected from the group consisting of transformers, stator and rotor of motors,
generator, alternators, field concentrators, chokes, relays, electromechanical
actuators and synchroresolvers.

A magnetic composite for AC applications with improved magnetic properties
(i.e. low hysteresis losses and low eddy current losses) is disclosed. The composite
comprises a consolidation of magnetizable metallic microlamellar particles each
having a top ad bottom surfaces and opposite ends. The top and bottom surfaces
are coated with a dielectric coating for increasing the resistivity of the composite
and reducing eddy current losses. The dielectric coating is made of a refractory
material and the ends of the lamellar particles are metallurgically bonded to each
other to reduce hysteresis losses of the composite. A process for manufacturing the
same is also disclosed. The composite is suitable for manufacturing devices for AC
applications such as transformers, stator and rotor of motors, generators,
alternators, field concentrators, chokes, relays, electromechanical actuators,
synchroresolvers, etc.

Documents:

1761-KOLNP-2005-FORM-27.pdf

1761-kolnp-2005-granted-abstract.pdf

1761-kolnp-2005-granted-assignment.pdf

1761-kolnp-2005-granted-claims.pdf

1761-kolnp-2005-granted-correspondence.pdf

1761-kolnp-2005-granted-description (complete).pdf

1761-kolnp-2005-granted-drawings.pdf

1761-kolnp-2005-granted-examination report.pdf

1761-kolnp-2005-granted-form 1.pdf

1761-kolnp-2005-granted-form 18.pdf

1761-kolnp-2005-granted-form 3.pdf

1761-kolnp-2005-granted-form 5.pdf

1761-kolnp-2005-granted-gpa.pdf

1761-kolnp-2005-granted-reply to examination report.pdf

1761-kolnp-2005-granted-specification.pdf

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Patent Number

227804

Indian Patent Application Number

1761/KOLNP/2005

PG Journal Number

04/2009

Publication Date

23-Jan-2009

Grant Date

20-Jan-2009

Date of Filing

05-Sep-2005

Name of Patentee

CORPORATION IMFINE INC.

Applicant Address

75 BOUL, DE MORTAGNE, BUREAU 119 BOUCHERVILLE, QUEBEC, J4B 6Y4

Inventors:

#	Inventor's Name	Inventor's Address
1	LEMIEUX, PATRICK	500 RUE DES CAPUCINES STE-JULIE, QUEBEC J3E 1V8

PCT International Classification Number

H01F 1/22

PCT International Application Number

PCT/CA2004/000147

PCT International Filing date

2004-02-04

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2,418497	2003-02-05	Canada