Title of Invention	NICKEL-BASED BRAZING ALLOY AND METHOD FOR BRAZING
Abstract	Nickel-based brazing alloy and method for brazing Brazing alloy with a composition consisting essentially of FeaNiRestCrbMocCudSi eBfPg, wherein 0 atomic % <= a <= 50 atomic %; 5 atomic % <= b <= 18 atomic %; 0.2 atomic % < c <= 3 atomic %; 4 atomic % <= e <= 15 atomic %; 4 atomic % <= f <= 15 atomic %; 0 atomic % <= g <= 6 atomic %; rest Ni, and wherein if 0 atomic % < a <= 50 atomic %; then 0.5 atomic % <= d < 3 atomic % and if a=0, then 0.5 atomic % <= d <= 5 atomic %.

Title of Invention

NICKEL-BASED BRAZING ALLOY AND METHOD FOR BRAZING

Abstract

Nickel-based brazing alloy and method for brazing Brazing alloy with a composition consisting essentially of FeaNiRestCrbMocCudSi eBfPg, wherein 0 atomic % <= a <= 50 atomic %; 5 atomic % <= b <= 18 atomic %; 0.2 atomic % < c <= 3 atomic %; 4 atomic % <= e <= 15 atomic %; 4 atomic % <= f <= 15 atomic %; 0 atomic % <= g <= 6 atomic %; rest Ni, and wherein if 0 atomic % < a <= 50 atomic %; then 0.5 atomic % <= d < 3 atomic % and if a=0, then 0.5 atomic % <= d <= 5 atomic %.

Full Text	Description Nickel-based brazing alloy and method for brazing [1] The invention relates to a nickel-based brazing alloy and to a method for brazing two or more components. [2] Soldering is a method for joining metal or ceramic components with the aid of a molten filler material identified as solder. Depending on the processing temperature of the solder, a distinction is made between soft soldering and brazing, the processing temperature typically exceeding the liquidus temperature of the solder by 10 ° C to 50 ° C. While soft solders are processed at temperatures below 450 ° C, brazing alloys are processed at temperatures above 450 ° C. Brazing alloys are used in application where a high mechanical strength of the joint and/or a high mechanical strength at elevated operating temperatures are/is required. [3] Components made of stainless steel or of Ni and Co alloys are often joined by means of Ni-based brazing alloys. The corrosion resistance of the joints produced by means of the brazing alloy is a critical criterion in many applications, in particular in stainDless steel heat exchangers and similar products. In order to increase the application tem- perature range and to improve corrosion resistance, EP 0108 959, for example, discloses a nickel-based brazing alloy with a chromium content of 17 to 20 atomic %. [4] This increased chromium content, however, has the disadvantage of increasing the liquidus temperature and thus the processing temperature. This results in undesirable coarse grain formation in the parent material and in a reduction of its mechanical strength, which is likewise undesirable in many applications. In addition, an increased chromium content of the brazing alloy can result in Cr-B and Cr-Si brittle phases in the brazed seam or in the parent material, which adversely affects the mechanical strength of the joint. [5] To reduce the chromium content and to solve these problems, WO 96/37335, for example, discloses a nickel-based brazing alloy with a molybdenum content up to 5 atomic % and a reduced chromium content between 9.5 and 16.5 atomic %. [6], From US 5,183,636 an iron-free brazing alloy is known, which comprises components preventing the diffusion of iron from the parent material into the brazing alloy and components which improve corrosion resistance. For this purpose, the iron- free brazing alloy contains copper, molybdenum, niobium and tantalum. This com- position is claimed to improve corrosion resistance, as the chromium content is maintained by the addition of niobium and tantalum and the brazed seam remains iron- free. [7] A disadvantage of these brazing alloys, however, lies in the fact that the corrosion resistance of the brazed joint is inadequate in aggressive media such as acidic media. In addition, the brazing alloy known from US 5,183,636 is very expensive owing to its components. [8] An object of the invention is to provide a nickel-based brazing alloy with improved corrosion resistance, which is also cost-effective. [9] According to the invention, a brazing alloy of a composition consisting essentially of [10] FegNRestCrbMocCu dSieBfPg [11] wherein 0 atomic % atomic % atomic %; 0 atomic % [12] wherein if 0 atomic % [13] and if a=0, then 0.5 atomic % [14] Two alternative compositions are, therefore, provided. In the first embodiment, the brazing alloy comprises iron and a copper content in the range 0.5 atomic % atomic %. In the second embodiment, the brazing alloy is iron free. In this em- bodiment, a slightly higher copper content may be provided so that the copper content may in the range 0.5 atomic % range for the iron-free brazing alloy is .0.5 atomic % containing first embodiment. [15] By the term 'consisting essentially of, it is to be understood that the brazing alloy may contain trace amounts of unavoidable impurities. Typical impurities may be the elements Al, S, Se, Ti and Zr. The total amount of impurities should be less than 2000 ppm, preferably less than 1000 ppm. [ 16] The brazing alloy of the invention includes both molybdenum and copper in amounts such that the corrosion resistance is improved over compositions including only one of molybdenum and copper. Surprisingly, it was found that this brazing alloy has a good corrosion resistance without any expensive additions of tantalum and niobium. [17] This good corrosion resistance is furthermore retained even at an iron content up to 50 atomic %. This further reduces raw material costs, since nickel is partially replaced by iron which is cheaper than nickel. These compositions are particularly suitable for applications where the cost of the material is an important factor. [18] In a further embodiment, the brazing alloy preferably combines an addition of 0.2 to 1.5 atomic % of molybdenum with an addition of 0.5 to 3 atomic % of copper to improve corrosion resistance. [19] The brazing alloy according to the invention has been found suitable for application in highly aggressive media, such as heat exchangers for internal combustion engines and exhaust gas recirculation coolers. In these applications, the brazed joint is exposed to reductive or oxidising acidic media, which may further include sulphate and/or nitrate and/or chloride ions. Brazed seams produced using the brazing alloy according to the invention also exhibit a good corrosion resistance in these aggressive media. Further applications for the brazing alloy according to the invention include the joining of two or more components of industrial-type stainless steel heat exchangers and of heat exchangers in cars and commercial vehicles, where aggressive media are generated. [20] The good corrosion resistance of the brazing solder according to the invention is achieved with a moderate chromium content of 5 to 18 atomic %, whereby the disad- vantages of high-chromium alloys are avoided. In contrast to a composition with an increased chromium content, the combined addition of Mo and Cu does not result in an undesirable increase in liquidus temperature and thus in the processing temperature of the brazing alloy. This chromium content ensures that the strong formation of Cr-B and Cr-Si brittle phases is avoided both in the brazed seam and in the parent material. A good corrosion resistance is provided by the addition of Mo and Cu in spite of the low chromium content. [21] The brazing alloy according to the invention has a liquidus temperature of less than 1200 ° C. This is desirable, because the maximum brazing temperature for many in- dustrial processes, in particular for joining stainless steel parent materials, is limited to approximately 1200 ° C. As a rule, brazing temperature is kept as low as possible because of undesirable coarse grain formation in the parent material at temperatures from 1000 ° C. This undesirable coarse grain formation results in a reduction of the mechanical strength of the parent material, which is critical for many technological ap- plications such as heat exchangers. This problem is significantly reduced by the brazing alloy according to the invention. [22] The brazing alloy is therefore reliable in industrial applications with a maximum soldering temperature limited to 1200 ° C. It provides for a reliable brazed joint. [23] In further embodiments, the brazing colder has an Si content of 7 % and/or a B content of 5 atomic %. [24] The elements boron, silicon and phosphorus are metalloid and glass-forming elements and permit the production of the brazing alloy as an amorphous, ductile foil. A higher content of these elements leads to a reduction of melting or liquidus tem- perature. If the content of glass-forming elements is too low, the foils solidify in a crystalline manner and become very brittle. If, on the other hand, the content of glass- forming elements is too high, the foils become brittle and can no longer be processed for technological applications. [25] The metalloid content is further chosen such that the brazed seam produced using a foil of brazing alloy has suitable mechanical properties. A high B content results in the separation of B hard phases, leading to a deterioration of the mechanical properties of the brazed joint. Boron reacts with chromium, likewise resulting in a noticeable reduction of corrosion resistance. A high Si content results in the formation of un- desirable Si hard phases in the brazed seam, which likewise reduces the strength of the soldered seam. [26] The brazing alloy according to any of the embodiments described above can be provided as a paste or as an amorphous, ductile brazing alloy foil. The brazing alloy according to the invention can be produced as a powder or as an amorphous, ductile foil, for example in a rapid solidification process. These brazing alloys are therefore available in various forms which can be adapted to different applications. [27] In one embodiment, the brazing alloy foil is up to 50%, preferably at least up to 80%, amorphous. [28] The brazing alloy foils according to the invention can be produced as ductile foils in increased strip thicknesses and increased strip widths. The brazing alloys according to the invention are therefore excellently suitable for casting with thicknesses of more than 20 urn, preferably of 20 µm mm, preferably 20 mm degree with nickel-based brazing alloys of prior art. [29] In one embodiment, a heat exchanger is provided with at least one brazed seam produced with a brazing alloy of a composition consisting essentially of [30] FegNRestCrbMocCu dSieBfPg, [31] wherein 0 atomic % atomic % atomic %; 0 atomic % [32] wherein if 0 atomic % [33] and if a=0, then 0.5 atomic % [34] In another embodiment, this brazed seam is produced using a brazing alloy of this composition in the form of an amorphous, ductile brazing alloy foil. The heat exchanger may have at least one brazed seam produced with a brazing alloy or an amorphous, ductile brazing alloy foil according to any of the embodiments described above. The brazed seam produced with an amorphous, ductile brazing alloy foil has a thickness of at least 20µm. [35] The brazed seam produced with an amorphous, ductile brazing alloy foil differs from a brazed seam produced by means of a crystalline powder in the size of the B and Si hard phases. [36] A method for joining two or more components, which comprises the following steps, is provided. A brazing alloy according to any of the embodiDments described above is applied between two or more of the metal components to be joined. The components to be joined have a higher melting temperature than the brazing alloy and may be made of stainless steel or an Ni or Co alloy. The brazing composite is heated to a temperature above the liquidus temperature of the brazing alloy and then cooled while a brazed joint forms between the components to be joined. The method may join the components by adhesive force or cohesively. [37] A further method for joining two or more components, which comprises the following steps, is provided. An amorphous, ductile brazing alloy foil according to any of the embodiments described above is applied between two or more of the metal components to be joined. The components to be joined have a higher melting tem- perature than the brazing alloy foil and may be made of stainless steel or an Ni or Co alloy. The brazing composite is heated to a temperature above the liquidus temperature of the brazing alloy foil and then cooled while a brazed joint forms between the components to be joined. [38] The components to be joined are preferably components of a heat exchanger or exhaust gas recirculation cooler or components of a fuel cell. These products require a reliable brazed joint which is completely leak-proof, resistant against corrosion at elevated operating temperatures, mechanically stable and merefore reliable. The brazing alloy foils according to the invention provide such a joint. [39] The brazing alloys and brazing alloy foils according to the invention can be used to produce one or more brazed seams in an object. The brazed object may be a heat exchanger, an exhaust gas recirculation cooler or a component of a fuel cell. In one embodiment, the brazed object is designed for use in a reductive or oxidising acidic medium, in another embodiment for use in a reductive medium and in yet another em- bodiment for use in an oxidising acidic medium which further contains sulphate and/or nitrate and/or chloride ions, or for use in a reductive or oxidising acidic medium of an internal combustion engine. / [40] The brazing alloys according to the invention are produced as amorphous, ho- mogeneous and ductile brazing alloy foils in a rapid solidification process in one em- bodiment of the method. For this purpose, a metal melt with the composition FeaNiRest CrbMOeCudSi eBfPg is provided, consisting essentially of [41] FeaNRestCrbMocCu dSieBfPg, [42] wherein 0 atomic % atomic % atomic %; 0 atomic % [43] wherein if 0 atomic % [44] and if a=0, then 0.5 atomic % [45] This melt is sprayed through a casting nozzle onto a casting wheel or casting drum and cooled at a rate of more than 105 ° C/s. The cast strip is then typically removed from the casting wheel at a temperature between 100 ° C and 300 ° C and directly wound to form a so-called coil or wound onto a reel to provide an amorphous, ductile brazing alloy foil. [46] In a further method, amorphous brazing alloy foils are used to join two or more components by adhesive force, the method comprising the following steps: [47] - Provision of a melt of FeaNRestCrbMocCudSi eBrPg, consisting essentially of [48] FeaNiReastCrbMocCu d SieBfPg, [49] wherein 0 atomic % atomic % atomic %; 0 atomic % [50] wherein if 0 atomic % [51] and if a=0, then 0.5 atomic % [52] - Production of an amorphous brazing alloy foil by rapid solidification of the melt on a moving cooling surface at a rate of more than approximately 10s ° C/s; [53] - Formation of a brazing composite by applying the brazing alloy foil between the metal components to be joined; [54] - Heating of the brazing composite to a temperature above the liquidus temperature of the brazing alloy foil; [55] - Cooling of the brazing composite accompanied by the formation of a joint between the metal components to be joined. [56] The process of joining by adhesive force as described above involves brazing with the nickel brazing alloy according to the invention, which is capable of producing perfect brazed joints without any joining faults. [57] The liquidus temperature of the brazing alloy according to the invention is less than 1200 ° C. The brazing alloy according to the invention can in particular be used to join metal components made of stainless steel and/or nickel and/or Co alloys by adhesive force. Such components typically include components used in heat exchangers or related products and in exhaust gas recirculation coolers. [58] The invention is described in detail below with reference to embodiments and com- parative examples. [59] Figure 1 illustrates the weight loss in a corrosion test on stainless steel samples with brazed joints of a first basic composition with additions of Mo and/or Cu; [60] Figure 2 illustrates the weight loss in a corrosion test on stainless steel samples with brazed joints of a second basic composition with various Mo additions; [61] Figure 3 illustrates the weight loss in a corrosion test on stainless steel samples with brazed joints of a second basic composition with various Cu additions; and [62] Figure 4 illustrates the weight loss in a corrosion test on stainless steel samples with brazed joints of a second basic composition with varying iron content. [63] At least partially amorphous nickel- and iron-based brazing alloy foils of various compositions were produced in a rapid solidification process. The corrosion resistance of brazed seams with additions of Cu, Mo or a combination of Cu and Mo was compared to that of brazing alloy foils without molybdenum and copper. [64] In a first embodiment, the corrosion resistance of a combination of Mo and Cu additions was compared to that of Mo only and Cu only in a first basic composition. At least partially amorphous brazing alloy foils were produced by means of rapid solidi- fication technology. The compositions of the foil are listed in Table 1. [65] In this first embodiment, the brazing alloy foils had a composition of 12.3 atomic % Cr, 3.7 atomic % Fe, 7.9 atomic % Si and 12.8 atomic % B, the rest being nickel. Further foils were produced with 12.3 atomic % Cr, 3.7 atomic % Fe, 7.9 atomic % Si and 12.8 atomic % B with additions of copper and/or molybdenum, the rest being nickel. One brazing alloy foil contains 2 atomic % of copper, a second foil 1 atomic % of molybdenum and a third foil 1 atomic % of molybdenum and 2 atomic % of copper. [66] Stainless steel samples (316L, 1.4404), wherein a base plate is joined to two tube sections, were brazed in a vacuum using the above foils at a temperature of 1200 ° C. The brazed components were placed in a corrosive medium with pH - and Cl- ions at 70 ° C. The weight loss of the various samples after 720 hours of exposure is shown in Figure 1. [67] Figure 1 shows clearly that an addition of Cu only or of Mo only results in an only . moderate improvement of corrosion resistance compared to a brazed joint produced without Mo and Cu. The lowest weight loss and therefore the best corrosion resistance is found in the brazing alloy containing both Mo and Cu. The combined addition of Mo and Cu provides a brazing alloy with improved corrosion resistance. [68] In a second embodiment, the influence of a combined addition of Mo and Cu on the corrosion resistance of a second basic composition was investigated. In this second embodiment, a brazing alloy with a combination of Mo and Cu additions was compared to copper-free brazing alloys with increasing Mo content. [69] At least partially amorphous brazing alloy foils were produced by means of rapid so- lidification technology. In this second embodiment, the brazing alloy foils had a basic composition of 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic % Si and 7 atomic % B, the rest being iron. Copper-free foils were produced with 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic % Si and 7 atomic % B with 0.5,1 and 1.5 atomic % molybdenum, the rest being iron. In addition, a foil was produced with 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic % Si and 7 atomic % B with an addition of 2 atomic % copper and 1 atomic % Mo, the rest being iron. These compositions are listed in Table 2. The second basic composition therefore contains significantly more iron than the first basic com- position. [70] Stainless steel samples were produced as in the first embodiment, and corrosion resistance was tested as described above. In the second embodiment, the samples were exposed for 864 hours, whereupon their weight loss was measured. [71] As Figure 2 shows, the alloy with a combined addition of Mo and Cu loses the least weight and has therefore the best corrosion resistance. The corrosion resistance of the alloy containing both Mo and Cu cannot be reached by simply varying the mo- lybdenum content in an alloy comprising only molybdenum and no copper. [72] In a third embodiment, the influence of a combined addition of Mo and Cu on the corrosion resistance of a third basic composition was investigated. At least partially amorphous brazing alloy foils were produced by means of rapid solidification techDnology. In this third embodiment, the brazing alloy foils had a basic composition of 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic % Si and 7 atomic % B, the rest being iron. A copper-free foil was produced with 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic % Si and 7 atomic % B with 1 atomic % molybdenum, the rest being iron. Mo- lybdenum-free foils were produced with 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic % Si and 7 atomic % B with an addition of 1 and 2 atomic % copper, each with 1 atomic % Mo, the rest being iron. These compositions are listed in Table 3. [73] Stainless steel samples were produced as in the first embodiment, and corrosion resistance was tested as described above. Figure 3 shows their weight loss after 720 hours' exposure. [74] Figure 3 shows that the corrosion resistance of brazing alloys with additions of Mo and Cu is noticeably better than that of alloys with Mo only. [75] In a fourth embodiment, the corrosion resistance of at least partially amorphous brazing alloy foils with a combination of 1 atomic % Mo and 1 atomic % Cu and in- creasing iron content was investigated. [76] The at least partially amorphous brazing alloy foils were produced by means of rapid solidification technology. At least partially amorphous foils with an Fe content of 0, 10,20,30,40,50,60 and 70 atomic %, each with a Cr content of 11 atomic %, an Si content of 9 atomic %, a B content of 9 atomic %, an Mo content of 1 atomic % and a Cu content of 2 atomic %, were produced, the rest being nickel. These compositions are listed in Table 4. [77] Figure 4 shows that the corrosion resistance of foils containing Mo and Cu remains virtually constant up to an Fe content of 50 atomic %. This offers the advantage that nickel can be replaced by iron up to an Fe content of 50 atomic % without significantly affecting corrosion resistance. As a result, raw material costs can be reduced. [78] Table 1 - Composition of the brazing alloy foils of the first embodiment We Claim: 1. Amorphous, ductile brazing alloy foil with a composition consisting essentially of FeaNiRCrbMocCu dSieBfPg, wherein 0 atomic % atomic % wherein if 0 atomic % %, and if a=0, then 0.5 atomic % 2. Amorphous, ductile brazing alloy foil as claimed in claim 1, wherein if a=0, then 0.5 atomic % 3. Amorphous, ductile brazing alloy foil as claimed in claim 1 or claim 2, wherein a Si content of 7 atomic % 4. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 3, wherein a Cr content of 5 atomic % 5. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 4, wherein a B content of 5 6. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 5, wherein an Fe content of 3 atomic % 7. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 6, wherein the brazing alloy foil is at least 80% amorphous. 8. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 7, comprising a thickness D wherein 20 µm 9. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 8, comprising a width B wherein 20 mm 10. Amorphous, ductile brazing alloy foil as claimed in claim 9, comprising a width B wherein 40 mm 11. Heat exchanger with at least one brazed seam produced with a brazing alloy foil as claimed in one of claims 1 to 7, wherein thickness of the brazed seam is > 20 µm. 12. Method for joining two or more components, comprising the following steps: - Application of an amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 10 between two or more components to be joined, the components to be joined having a higher melting temperature than the brazing alloy foil; - Heating of the brazing composite to a temperature above the liquidus temperature of the brazing alloy foil; - Cooling of the brazing composite accompanied by the formation of a brazed joint between the components to be joined. 13. Method as claimed in claim 12 for joining two or more metal components, wherein the components to be joined are components of a heat exchanger or an exhaust gas recirculation cooler or a fuel cell. 14. Method for joining two or more components, comprising the following steps: Provision of melt consisting essentially of FeaNiRCrbMocCu dSieBfPg, wherein 0 atomic % atomic % wherein if 0 atomic % %, - and if a=0, then 0.5 atomic % - Production of an amorphous brazing alloy foil by rapid solidification of the melt on a moving cooling surface at a rate of more than 105 oC/s; - Formation of a brazing composite by applying the brazing alloy foil between the components to be joined; - Heating of the brazing composite to a temperature above the liquidus temperature of the brazing alloy foil; - Cooling of the brazing composite accompanied by the formation of a brazed joint between the components to be joined. 15. Method for the production of an amorphous, ductile brazing alloy foil, comprising the following steps: - Provision of a melt consisting essentially of FeaNiRCrbMocCu dSieBfPg, wherein 0 atomic % atomic % wherein if 0 atomic % %, - and if a=0, then 0.5 atomic % - Production of an amorphous brazing alloy foil by rapid solidification of the melt on a moving cooling surface at a rate of more than 105 ° C/s. 16. Brazed object, wherein at least one brazed seam is produced from an amorphous, ductile brazing alloy foil as claimed in any of claims 1 to 10. 17. Brazed object as claimed in claim 16, for use as a heat exchanger, an exhaust gas recirculation cooler or a component of a fuel cell. 18. Brazed object as claimed in claim 16, for use in a reductive or oxidising acidic medium. 19. Brazed object as claimed in claim 16, for use in a reductive or oxidising acidic medium which further contains sulphate and/or nitrate and/or chloride ions. 20. Brazed object as claimed in claim 16, for use in a reductive or oxidising acidic medium of an internal combustion engine. NICKEL-BASED BRAZING ALLOY AND METHOD FOR BRAZING ABSTRACT Nickel-based brazing alloy and method for brazing Brazing alloy with a composition consisting essentially of FeaNiRestCrbMocCudSi eBfPg, wherein 0 atomic % atomic %; 5 atomic % % %; rest Ni, and wherein if 0 atomic % atomic % and if a=0, then 0.5 atomic %

Full Text

Description
Nickel-based brazing alloy and method for brazing
[1] The invention relates to a nickel-based brazing alloy and to a method for brazing two
or more components.
[2] Soldering is a method for joining metal or ceramic components with the aid of a
molten filler material identified as solder. Depending on the processing temperature of
the solder, a distinction is made between soft soldering and brazing, the processing
temperature typically exceeding the liquidus temperature of the solder by 10 ° C to 50
° C. While soft solders are processed at temperatures below 450 ° C, brazing alloys are
processed at temperatures above 450 ° C. Brazing alloys are used in application where
a high mechanical strength of the joint and/or a high mechanical strength at elevated
operating temperatures are/is required.
[3] Components made of stainless steel or of Ni and Co alloys are often joined by means
of Ni-based brazing alloys. The corrosion resistance of the joints produced by means of
the brazing alloy is a critical criterion in many applications, in particular in stainDless
steel heat exchangers and similar products. In order to increase the application tem-
perature range and to improve corrosion resistance, EP 0108 959, for example,
discloses a nickel-based brazing alloy with a chromium content of 17 to 20 atomic %.
[4] This increased chromium content, however, has the disadvantage of increasing the
liquidus temperature and thus the processing temperature. This results in undesirable
coarse grain formation in the parent material and in a reduction of its mechanical
strength, which is likewise undesirable in many applications. In addition, an increased
chromium content of the brazing alloy can result in Cr-B and Cr-Si brittle phases in the
brazed seam or in the parent material, which adversely affects the mechanical strength
of the joint.
[5] To reduce the chromium content and to solve these problems, WO 96/37335, for
example, discloses a nickel-based brazing alloy with a molybdenum content up to 5
atomic % and a reduced chromium content between 9.5 and 16.5 atomic %.
[6], From US 5,183,636 an iron-free brazing alloy is known, which comprises
components preventing the diffusion of iron from the parent material into the brazing
alloy and components which improve corrosion resistance. For this purpose, the iron-
free brazing alloy contains copper, molybdenum, niobium and tantalum. This com-
position is claimed to improve corrosion resistance, as the chromium content is
maintained by the addition of niobium and tantalum and the brazed seam remains iron-
free.
[7] A disadvantage of these brazing alloys, however, lies in the fact that the corrosion
resistance of the brazed joint is inadequate in aggressive media such as acidic media.

In addition, the brazing alloy known from US 5,183,636 is very expensive owing to its
components.
[8] An object of the invention is to provide a nickel-based brazing alloy with improved
corrosion resistance, which is also cost-effective.
[9] According to the invention, a brazing alloy of a composition consisting essentially of
[10] FegNRestCrbMocCu dSieBfPg
[11] wherein 0 atomic % atomic % atomic %; 0 atomic % [12] wherein if 0 atomic % [13] and if a=0, then 0.5 atomic % [14] Two alternative compositions are, therefore, provided. In the first embodiment, the
brazing alloy comprises iron and a copper content in the range 0.5 atomic % atomic %. In the second embodiment, the brazing alloy is iron free. In this em-
bodiment, a slightly higher copper content may be provided so that the copper content
may in the range 0.5 atomic % range for the iron-free brazing alloy is .0.5 atomic % containing first embodiment.
[15] By the term 'consisting essentially of, it is to be understood that the brazing alloy
may contain trace amounts of unavoidable impurities. Typical impurities may be the
elements Al, S, Se, Ti and Zr. The total amount of impurities should be less than 2000
ppm, preferably less than 1000 ppm.
[ 16] The brazing alloy of the invention includes both molybdenum and copper in amounts
such that the corrosion resistance is improved over compositions including only one of
molybdenum and copper. Surprisingly, it was found that this brazing alloy has a good
corrosion resistance without any expensive additions of tantalum and niobium.
[17] This good corrosion resistance is furthermore retained even at an iron content up to
50 atomic %. This further reduces raw material costs, since nickel is partially replaced
by iron which is cheaper than nickel. These compositions are particularly suitable for
applications where the cost of the material is an important factor.
[18] In a further embodiment, the brazing alloy preferably combines an addition of 0.2 to
1.5 atomic % of molybdenum with an addition of 0.5 to 3 atomic % of copper to
improve corrosion resistance.
[19] The brazing alloy according to the invention has been found suitable for application
in highly aggressive media, such as heat exchangers for internal combustion engines
and exhaust gas recirculation coolers. In these applications, the brazed joint is exposed
to reductive or oxidising acidic media, which may further include sulphate and/or
nitrate and/or chloride ions. Brazed seams produced using the brazing alloy according

to the invention also exhibit a good corrosion resistance in these aggressive media.
Further applications for the brazing alloy according to the invention include the joining
of two or more components of industrial-type stainless steel heat exchangers and of
heat exchangers in cars and commercial vehicles, where aggressive media are
generated.
[20] The good corrosion resistance of the brazing solder according to the invention is
achieved with a moderate chromium content of 5 to 18 atomic %, whereby the disad-
vantages of high-chromium alloys are avoided. In contrast to a composition with an
increased chromium content, the combined addition of Mo and Cu does not result in an
undesirable increase in liquidus temperature and thus in the processing temperature of
the brazing alloy. This chromium content ensures that the strong formation of Cr-B and
Cr-Si brittle phases is avoided both in the brazed seam and in the parent material. A
good corrosion resistance is provided by the addition of Mo and Cu in spite of the low
chromium content.
[21] The brazing alloy according to the invention has a liquidus temperature of less than
1200 ° C. This is desirable, because the maximum brazing temperature for many in-
dustrial processes, in particular for joining stainless steel parent materials, is limited to
approximately 1200 ° C. As a rule, brazing temperature is kept as low as possible
because of undesirable coarse grain formation in the parent material at temperatures
from 1000 ° C. This undesirable coarse grain formation results in a reduction of the
mechanical strength of the parent material, which is critical for many technological ap-
plications such as heat exchangers. This problem is significantly reduced by the
brazing alloy according to the invention.
[22] The brazing alloy is therefore reliable in industrial applications with a maximum
soldering temperature limited to 1200 ° C. It provides for a reliable brazed joint.
[23] In further embodiments, the brazing colder has an Si content of 7 % and/or a B content of 5 atomic %.
[24] The elements boron, silicon and phosphorus are metalloid and glass-forming
elements and permit the production of the brazing alloy as an amorphous, ductile foil.
A higher content of these elements leads to a reduction of melting or liquidus tem-
perature. If the content of glass-forming elements is too low, the foils solidify in a
crystalline manner and become very brittle. If, on the other hand, the content of glass-
forming elements is too high, the foils become brittle and can no longer be processed
for technological applications.
[25] The metalloid content is further chosen such that the brazed seam produced using a
foil of brazing alloy has suitable mechanical properties. A high B content results in the
separation of B hard phases, leading to a deterioration of the mechanical properties of

the brazed joint. Boron reacts with chromium, likewise resulting in a noticeable
reduction of corrosion resistance. A high Si content results in the formation of un-
desirable Si hard phases in the brazed seam, which likewise reduces the strength of the
soldered seam.
[26] The brazing alloy according to any of the embodiments described above can be
provided as a paste or as an amorphous, ductile brazing alloy foil. The brazing alloy
according to the invention can be produced as a powder or as an amorphous, ductile
foil, for example in a rapid solidification process. These brazing alloys are therefore
available in various forms which can be adapted to different applications.
[27] In one embodiment, the brazing alloy foil is up to 50%, preferably at least up to 80%,
amorphous.
[28] The brazing alloy foils according to the invention can be produced as ductile foils in
increased strip thicknesses and increased strip widths. The brazing alloys according to
the invention are therefore excellently suitable for casting with thicknesses of more
than 20 urn, preferably of 20 µm mm, preferably 20 mm degree with nickel-based brazing alloys of prior art.
[29] In one embodiment, a heat exchanger is provided with at least one brazed seam
produced with a brazing alloy of a composition consisting essentially of
[30] FegNRestCrbMocCu dSieBfPg,
[31] wherein 0 atomic % atomic % atomic %; 0 atomic % [32] wherein if 0 atomic % [33] and if a=0, then 0.5 atomic % [34] In another embodiment, this brazed seam is produced using a brazing alloy of this
composition in the form of an amorphous, ductile brazing alloy foil. The heat
exchanger may have at least one brazed seam produced with a brazing alloy or an
amorphous, ductile brazing alloy foil according to any of the embodiments described
above. The brazed seam produced with an amorphous, ductile brazing alloy foil has a
thickness of at least 20µm.
[35] The brazed seam produced with an amorphous, ductile brazing alloy foil differs from
a brazed seam produced by means of a crystalline powder in the size of the B and Si
hard phases.
[36] A method for joining two or more components, which comprises the following steps,
is provided. A brazing alloy according to any of the embodiDments described above is
applied between two or more of the metal components to be joined. The components to
be joined have a higher melting temperature than the brazing alloy and may be made of

stainless steel or an Ni or Co alloy. The brazing composite is heated to a temperature
above the liquidus temperature of the brazing alloy and then cooled while a brazed
joint forms between the components to be joined. The method may join the
components by adhesive force or cohesively.
[37] A further method for joining two or more components, which comprises the
following steps, is provided. An amorphous, ductile brazing alloy foil according to any
of the embodiments described above is applied between two or more of the metal
components to be joined. The components to be joined have a higher melting tem-
perature than the brazing alloy foil and may be made of stainless steel or an Ni or Co
alloy. The brazing composite is heated to a temperature above the liquidus temperature
of the brazing alloy foil and then cooled while a brazed joint forms between the
components to be joined.
[38] The components to be joined are preferably components of a heat exchanger or
exhaust gas recirculation cooler or components of a fuel cell. These products require a
reliable brazed joint which is completely leak-proof, resistant against corrosion at
elevated operating temperatures, mechanically stable and merefore reliable. The
brazing alloy foils according to the invention provide such a joint.
[39] The brazing alloys and brazing alloy foils according to the invention can be used to
produce one or more brazed seams in an object. The brazed object may be a heat
exchanger, an exhaust gas recirculation cooler or a component of a fuel cell. In one
embodiment, the brazed object is designed for use in a reductive or oxidising acidic
medium, in another embodiment for use in a reductive medium and in yet another em-
bodiment for use in an oxidising acidic medium which further contains sulphate and/or
nitrate and/or chloride ions, or for use in a reductive or oxidising acidic medium of an
internal combustion engine. /
[40] The brazing alloys according to the invention are produced as amorphous, ho-
mogeneous and ductile brazing alloy foils in a rapid solidification process in one em-
bodiment of the method. For this purpose, a metal melt with the composition FeaNiRest
CrbMOeCudSi eBfPg is provided, consisting essentially of
[41] FeaNRestCrbMocCu dSieBfPg,
[42] wherein 0 atomic % atomic % atomic %; 0 atomic % [43] wherein if 0 atomic % [44] and if a=0, then 0.5 atomic % [45] This melt is sprayed through a casting nozzle onto a casting wheel or casting drum
and cooled at a rate of more than 105 ° C/s. The cast strip is then typically removed
from the casting wheel at a temperature between 100 ° C and 300 ° C and directly

wound to form a so-called coil or wound onto a reel to provide an amorphous, ductile
brazing alloy foil.
[46] In a further method, amorphous brazing alloy foils are used to join two or more
components by adhesive force, the method comprising the following steps:
[47] - Provision of a melt of FeaNRestCrbMocCudSi eBrPg, consisting essentially of
[48] FeaNiReastCrbMocCu d SieBfPg,
[49] wherein 0 atomic % atomic % atomic %; 0 atomic % [50] wherein if 0 atomic % [51] and if a=0, then 0.5 atomic % [52] - Production of an amorphous brazing alloy foil by rapid solidification of the melt on
a moving cooling surface at a rate of more than approximately 10s ° C/s;
[53] - Formation of a brazing composite by applying the brazing alloy foil between the
metal components to be joined;
[54] - Heating of the brazing composite to a temperature above the liquidus temperature
of the brazing alloy foil;
[55] - Cooling of the brazing composite accompanied by the formation of a joint between
the metal components to be joined.
[56] The process of joining by adhesive force as described above involves brazing with
the nickel brazing alloy according to the invention, which is capable of producing
perfect brazed joints without any joining faults.
[57] The liquidus temperature of the brazing alloy according to the invention is less than
1200 ° C. The brazing alloy according to the invention can in particular be used to join
metal components made of stainless steel and/or nickel and/or Co alloys by adhesive
force. Such components typically include components used in heat exchangers or
related products and in exhaust gas recirculation coolers.
[58] The invention is described in detail below with reference to embodiments and com-
parative examples.
[59] Figure 1 illustrates the weight loss in a corrosion test on stainless steel samples with
brazed joints of a first basic composition with additions of Mo and/or Cu;
[60] Figure 2 illustrates the weight loss in a corrosion test on stainless steel samples with
brazed joints of a second basic composition with various Mo additions;
[61] Figure 3 illustrates the weight loss in a corrosion test on stainless steel samples with
brazed joints of a second basic composition with various Cu additions; and
[62] Figure 4 illustrates the weight loss in a corrosion test on stainless steel samples with
brazed joints of a second basic composition with varying iron content.
[63] At least partially amorphous nickel- and iron-based brazing alloy foils of various

compositions were produced in a rapid solidification process. The corrosion resistance
of brazed seams with additions of Cu, Mo or a combination of Cu and Mo was
compared to that of brazing alloy foils without molybdenum and copper.
[64] In a first embodiment, the corrosion resistance of a combination of Mo and Cu
additions was compared to that of Mo only and Cu only in a first basic composition. At
least partially amorphous brazing alloy foils were produced by means of rapid solidi-
fication technology. The compositions of the foil are listed in Table 1.
[65] In this first embodiment, the brazing alloy foils had a composition of 12.3 atomic %
Cr, 3.7 atomic % Fe, 7.9 atomic % Si and 12.8 atomic % B, the rest being nickel.
Further foils were produced with 12.3 atomic % Cr, 3.7 atomic % Fe, 7.9 atomic % Si
and 12.8 atomic % B with additions of copper and/or molybdenum, the rest being
nickel. One brazing alloy foil contains 2 atomic % of copper, a second foil 1 atomic %
of molybdenum and a third foil 1 atomic % of molybdenum and 2 atomic % of copper.
[66] Stainless steel samples (316L, 1.4404), wherein a base plate is joined to two tube
sections, were brazed in a vacuum using the above foils at a temperature of 1200 ° C.
The brazed components were placed in a corrosive medium with pH - and Cl- ions at 70 ° C. The weight loss of the various samples after 720 hours of
exposure is shown in Figure 1.
[67] Figure 1 shows clearly that an addition of Cu only or of Mo only results in an only .
moderate improvement of corrosion resistance compared to a brazed joint produced
without Mo and Cu. The lowest weight loss and therefore the best corrosion resistance
is found in the brazing alloy containing both Mo and Cu. The combined addition of
Mo and Cu provides a brazing alloy with improved corrosion resistance.
[68] In a second embodiment, the influence of a combined addition of Mo and Cu on the
corrosion resistance of a second basic composition was investigated. In this second
embodiment, a brazing alloy with a combination of Mo and Cu additions was
compared to copper-free brazing alloys with increasing Mo content.
[69] At least partially amorphous brazing alloy foils were produced by means of rapid so-
lidification technology. In this second embodiment, the brazing alloy foils had a basic
composition of 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic % Si and 7 atomic % B,
the rest being iron. Copper-free foils were produced with 11 atomic % Cr, 35 atomic %
Ni, 11.5 atomic % Si and 7 atomic % B with 0.5,1 and 1.5 atomic % molybdenum, the
rest being iron. In addition, a foil was produced with 11 atomic % Cr, 35 atomic % Ni,
11.5 atomic % Si and 7 atomic % B with an addition of 2 atomic % copper and 1
atomic % Mo, the rest being iron. These compositions are listed in Table 2. The second
basic composition therefore contains significantly more iron than the first basic com-
position.
[70] Stainless steel samples were produced as in the first embodiment, and corrosion

resistance was tested as described above. In the second embodiment, the samples were
exposed for 864 hours, whereupon their weight loss was measured.
[71] As Figure 2 shows, the alloy with a combined addition of Mo and Cu loses the least
weight and has therefore the best corrosion resistance. The corrosion resistance of the
alloy containing both Mo and Cu cannot be reached by simply varying the mo-
lybdenum content in an alloy comprising only molybdenum and no copper.
[72] In a third embodiment, the influence of a combined addition of Mo and Cu on the
corrosion resistance of a third basic composition was investigated. At least partially
amorphous brazing alloy foils were produced by means of rapid solidification
techDnology. In this third embodiment, the brazing alloy foils had a basic composition
of 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic % Si and 7 atomic % B, the rest being
iron. A copper-free foil was produced with 11 atomic % Cr, 35 atomic % Ni, 11.5
atomic % Si and 7 atomic % B with 1 atomic % molybdenum, the rest being iron. Mo-
lybdenum-free foils were produced with 11 atomic % Cr, 35 atomic % Ni, 11.5 atomic
% Si and 7 atomic % B with an addition of 1 and 2 atomic % copper, each with 1
atomic % Mo, the rest being iron. These compositions are listed in Table 3.
[73] Stainless steel samples were produced as in the first embodiment, and corrosion
resistance was tested as described above. Figure 3 shows their weight loss after 720
hours' exposure.
[74] Figure 3 shows that the corrosion resistance of brazing alloys with additions of Mo
and Cu is noticeably better than that of alloys with Mo only.
[75] In a fourth embodiment, the corrosion resistance of at least partially amorphous
brazing alloy foils with a combination of 1 atomic % Mo and 1 atomic % Cu and in-
creasing iron content was investigated.
[76] The at least partially amorphous brazing alloy foils were produced by means of rapid
solidification technology. At least partially amorphous foils with an Fe content of 0,
10,20,30,40,50,60 and 70 atomic %, each with a Cr content of 11 atomic %, an Si
content of 9 atomic %, a B content of 9 atomic %, an Mo content of 1 atomic % and a
Cu content of 2 atomic %, were produced, the rest being nickel. These compositions
are listed in Table 4.
[77] Figure 4 shows that the corrosion resistance of foils containing Mo and Cu remains
virtually constant up to an Fe content of 50 atomic %. This offers the advantage that
nickel can be replaced by iron up to an Fe content of 50 atomic % without significantly
affecting corrosion resistance. As a result, raw material costs can be reduced.
[78] Table 1 - Composition of the brazing alloy foils of the first embodiment

We Claim:
1. Amorphous, ductile brazing alloy foil with a composition consisting essentially of
FeaNiRCrbMocCu dSieBfPg,
wherein 0 atomic % atomic % wherein if 0 atomic % %,
and if a=0, then 0.5 atomic % 2. Amorphous, ductile brazing alloy foil as claimed in claim 1, wherein
if a=0, then 0.5 atomic % 3. Amorphous, ductile brazing alloy foil as claimed in claim 1 or claim 2,
wherein
a Si content of 7 atomic % 4. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 3,
wherein
a Cr content of 5 atomic % 5. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 4,
wherein
a B content of 5 6. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 5,
wherein
an Fe content of 3 atomic % 7. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 6,
wherein
the brazing alloy foil is at least 80% amorphous.

8. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 7,
comprising
a thickness D wherein 20 µm 9. Amorphous, ductile brazing alloy foil as claimed in one of claims 1 to 8,
comprising
a width B wherein 20 mm 10. Amorphous, ductile brazing alloy foil as claimed in claim 9,
comprising
a width B wherein 40 mm 11. Heat exchanger with at least one brazed seam produced with a brazing alloy foil as
claimed in one of claims 1 to 7,
wherein
thickness of the brazed seam is > 20 µm.
12. Method for joining two or more components, comprising the following steps:
- Application of an amorphous, ductile brazing alloy foil as claimed in one of
claims 1 to 10 between two or more components to be joined, the components to be joined
having a higher melting temperature than the brazing alloy foil;
- Heating of the brazing composite to a temperature above the liquidus temperature of the
brazing alloy foil;
- Cooling of the brazing composite accompanied by the formation of a brazed
joint between the components to be joined.
13. Method as claimed in claim 12 for joining two or more metal components,
wherein
the components to be joined are components of a heat exchanger or an exhaust gas
recirculation cooler or a fuel cell.
14. Method for joining two or more components, comprising the following steps:

Provision of melt consisting essentially of
FeaNiRCrbMocCu dSieBfPg,
wherein 0 atomic % atomic % wherein if 0 atomic % %,
- and if a=0, then 0.5 atomic % - Production of an amorphous brazing alloy foil by rapid solidification of the
melt on a moving cooling surface at a rate of more than 105 oC/s;
- Formation of a brazing composite by applying the brazing alloy foil between
the components to be joined;
- Heating of the brazing composite to a temperature above the liquidus temperature of the
brazing alloy foil;
- Cooling of the brazing composite accompanied by the formation of a brazed
joint between the components to be joined.
15. Method for the production of an amorphous, ductile brazing alloy foil,
comprising the following steps:
- Provision of a melt consisting essentially of
FeaNiRCrbMocCu dSieBfPg,
wherein 0 atomic % atomic % wherein if 0 atomic % %,
- and if a=0, then 0.5 atomic % - Production of an amorphous brazing alloy foil by rapid solidification of the
melt on a moving cooling surface at a rate of more than 105 ° C/s.
16. Brazed object, wherein at least one brazed seam is produced from an amorphous,
ductile brazing alloy foil as claimed in any of claims 1 to 10.

17. Brazed object as claimed in claim 16, for use as a heat exchanger, an exhaust gas
recirculation cooler or a component of a fuel cell.
18. Brazed object as claimed in claim 16, for use in a reductive or oxidising acidic
medium.
19. Brazed object as claimed in claim 16, for use in a reductive or oxidising acidic
medium which further contains sulphate and/or nitrate and/or chloride ions.
20. Brazed object as claimed in claim 16, for use in a reductive or oxidising acidic
medium of an internal combustion engine.

NICKEL-BASED BRAZING ALLOY AND METHOD FOR BRAZING
ABSTRACT

Nickel-based brazing alloy and method for brazing Brazing alloy with a composition
consisting essentially of FeaNiRestCrbMocCudSi eBfPg, wherein 0 atomic % atomic %; 5 atomic % % %; rest Ni, and wherein if 0 atomic % atomic % and if a=0, then 0.5 atomic %

NICKEL-BASED BRAZING ALLOY AND METHOD FOR BRAZING

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