Title of Invention

"A COMPOSITE WIRE FOR PRODUCING A WEAR RESISTANT AND CORROSION RESISTANT COATING ON A SUBSTRATE"

Abstract

A COMPOSITE WIRE FOR PRODUCING A WEAR RESISTANT AND CORROSION RESISTANT COATING ON A SUBSTRATE The present invention relates to a composite wire for producing a wear resistant and corrosion resistant coating on a substrate, said composite wire consisting of a tubular metallic outer sheath encapsulating a powdered inner core, said inner core compring a mixture of boron carbide of at least 35 % by weight, and chrome carbide in an amount between 67 %-233 % by weight of the amount of boron carbide.

Full Text

TECHNICAL FIELD This application claims priority to U.S. provisionaL Application No. 60/476,875, filed on June 6, 2003. The present invention relates to coatings for substrates, particularly metallic substrates. More specifically, the invention relates to composite wires or cored wires for forming wear-resistant and corrosion-resistant coatings on metallic substrates by thermal spraying processes, spray and fuse processes, or by welding techniques. The invention also relates to methods of employing the composite or cored wires to apply wear-resistant and corrosion resistant coatings to substrates. BACKGROUND ART Thermal spraying, i.e. the generic name for a class of processes that allow the depositing molten of semi-molten materials onto a substrate to form a wear of corrosion resistant coating, has been known in various forms for many years. Thermal spraying processes include plasma, flame, arc-plasma, arc and combustion spraying. Arc spraying is a form of thermal spraying which involves feeding two electrically conductive wires towards one another so that an arc is struck between the tips of the wires to melt the wire tips . The molten material is then atomized and sprayed onto a substrate by compressed gas. This form of thermal spraying is widely used to provide corrosion-resistant coatings on various metallic articles. For example, U.S. Patent No, 6,156,443 (Dallaire, et al .) discloses coatings that are formed by arc spraying cored wires onto metallic articles exposed to erodent particles. 'The cored wires are composed of a sheath of ductile metal, such as iron, low 1 carbon steel, or ductile stainless steel, and a core coarse ferroboron particles. The resulting coatings are designed to include iron boride phases having mean sizes equal to or larger than the sizes at the erodent particles. Another thermal spraying proecess is described in U.S. Patent Mo. 5,837,336 (Daliaire, et al.), which discloses a process for producing composite coatings comprising fine titanium diboride particles or crystals distributed throughout a stainleass steel matrix by are spraying cored wires onto a metallic substrate. The cored wires typically comprise a stainless steel outer sheath and an inner core of compacted powders including titanium diboride and a metal or metal alloy. The particles or crystals in these gs impart hardnese to the soft stainless steel matrix and the resistance of the coatings to hard abrasive media. The metal components of the cored wires used to form the coatings disclosed in both U.S, Patent Nos. S,156,443 (Dallaire, et a.l.) and 5,837,326 (Dallaire, et al.) are not highly alloyed, and consequently the coatings tend to be susceptible to corrosion attack in certain high temperature corrosive conditions, such as in boiler applications. Generally, the binder metal (i.e,, the metal of the outer sheath) in a wear-rosistant coating is critical to the performance of the coating in, corrosive conditions such as those encountered in boilers, For example, coatings with ironbased binder alloys, such as Armacor Mw, exhibit extensive binder-material. corrosion in boiler conditions, resulting in wear of the coatings. The consequent weaKening of the can also lead to premature coating failure due to complete of the protective layer. Furthermore, the magnetic of these coatings prevent thickness using standard equipment, such as Elcometers. U.S. Patent Wo. 4,741,974 (Longo, et al.) disclosen a e wire for forming wear resistant coatings wherein the wire i s formed of. an alloy sheath having iron, nickel, or cobalt as a major component. The core of the composites wire is formed of powder that includes boron or boron carbide. Due to its extremo hardness, boron carbide is employed in coatings where. wear or abrasion is of primary concern. However, as with other conventional composite wires, in high- temperature corrosive environment, the wear resistant coatings may experience accelerated wear. DISCLOSORE OF. THE Accordingly, a composites wire ie provided for producing a wear resistant and corrosion resistant coating on a substrate by thermal spraying, spray and fuses, or welding techniques. While the coating produced by tho composite wire ot the present invention is suitable for all temperature ranges, the physical properties of the coating are particularly well suited, for hightemperature erosion- corrosion environments. The reeultant coating exhibits good hardness toughness, and bonding characteristios. The composite wire generally comprises a metallic outer sheath and an inner core containing boron carbide (BC) and chrome carbide (CrC) . The metallic outer sheath may be formed of an essentially pure metal or on alloy. As stated above, the binder is generally considered to be critical to the performance of a coating and the binder selection will depend -upon several factors including the environment to which the coated substrate will be exposed . The composite wire of the present invention is manufactured by conventional techniques wherein the specially formulated powder core is encapsulated by the outer sheath, The terms "composite wire" and "cored wire" are used aynonymously herein to describe such a w i r e . T h e chrome carbide/boron carbide formulation of the inner core provides a substantial improvement to conventional coatings deposited by conventional composite wires. The combination of chorme carbide and boron carbide gives added wear rosistance, increases metal binder hardness. improves bonding of the coating to the substrate, and inhibits oxide formation. The outer sheath may be constructed of any metal or alloy. Suitable binder material includes, but is not limited ho, iron, carbon and low alloy steels, stainless steels, nickel, nickel alloys, such as nickel -copper, nickel-cbromium, nickel-chrome -iron, and nickel -molybdenum alloys, copper, brasees, bronzes, aluminum bronzes, aluminum, aluminum alloys (ixxx - 7xxx) , titanium, titanium alloya, cobalt alloya, molybdenum and nolybdenum alloys, tantalum and tantalum alloys. The combination of these binder with the inner core powder of the present invention resulte in coatings having superior physical properties over conventional coatings, In addition to the composite wires discussed above, a method of forming a wear resistant and corrosion resistant coating on a substrate is also provided. The method generally include the steps of providing a composite wire having and outor sheath formed from a metal or alloy, and an inner core comprising boron carbide and chrome carbide; and coating a substrste by employing the composite wire in conjunction with thermal spraying, spray and fuse or welding techniques, BREIF DESCRIPTION OF THE Figure I is an electron micrograph of a cross section of an alloy 625 arc sprayed coating. Figure 2 is an ojectron micrograph of a cross section of an alloy 625/BC-CrC are sprayed coating, BEST MODE FOR CARRYING OUT THE In the following detailed description of the preferred embodiments , it is to be understood that other embodiments may be utilized and structural changes may bts made without departing from the scope of the present invention. The coatings according to the present invention are specifically designed for articles subjected to wear and/or corrosion. Such article include, for example, boiler tubes, hydraulic piston rods/ pump casings, rollers in the paper and steel industry, wear plates, journals and shafts, and turbine blades and casings. In one; application, the coatings are designed to protect boiler tubes against erosion-corrosicn related wantage and arc applied to the boiler tubes by means of a conventional arc spraying apparatus. However, it will be appreciated from the description bo low that the coatings could also be applied to the boiler tubes by other thermal spraying apparatus employing wires as the feed material using fusing equipment, or by suitable welding techniques. Are opraying methods and apparatus are well documented in the art, see for example, U.S, PatentNos. 5,155,443 (Dallaire, et al.) 5,837,326 (Dallaire, ct al.); European Patent No. EP 0 522 438 [Zurccki et a l . ) ; and PCT Patent No. WO 90/00574 (Seitz), the disclosures of which are incorporated by reference. The coatings of the present invention are formed from composite wires, which are fed through a conventional arc spraying apparatus, such as the apparatus disclosed in PCT Patent No, WO 01/08810 (Seitz), the diaclonure of which is incorporated herein by reference. The composite wires of the present invention comprise an outer sheath formed from a metal ox alloy. In one embodiment of the invention, which is particularity for the high temperature erosion-corrosion environment found in boiler application, the cored wires comprise an outer tubular sheath formed from a chromium bearing/ nickel base alloy such as an alloy 625, and an inner core, which comprises boron carbide and chrome carbide. The preferred inner core formulation preferably comprises chrome carbide in an amount between about 25% and about 400% by weight of the amount of boron carbide. In other words, the ratio of carome carbide to boron carbide preferably ranges between about 1:1 to about 4:1. More preferably, the inner core comprises chrome carbide in an amount between about 67% and about 230% by weight of the amount of boron carbides. In other words, the ratio of chrome carbide to boron carbide preferably rariges between about 1:1.5 to about 2,3:1. In one preferred embodiment, the inner core comprises about 100% by weight, of chrome carbide relative to the amount of boron carbide, in other words the amounts of chrome carbide and boron carbide are substantially equivalent. The chrome carbide in the inner core incerases the wear resistance at the deposited coating or weld overlay, The chrome carbide is retained during the thermal apraying or welding, and is present in molten form within the coating structure during application. However, this benefit accrues on a eliding scale - the more chrome carbide used the better the result, but at the expense of displacing boron carbide and its benaficial effects. Conversely most of the boron carbide does not appear to survive as a carbide during application of the coating. The boron carbide breaks up in the arc as uncontaminated boron and carbon, which both have hardening effects. The hardening effect increases the of: the metal of the outer steath through alloying and/or diffusion procesees. Some of the larger particles of boron carbide may curvive the are. Those particles add to the wear resistance, much like the chrome carbide, but the resistance achieved with large part idea of boron carbide is not as effective as that achieved with chrome carbide. Furthermore, the boron carbide inhibits the formation of oxides in the molten outer sheath during spraying. To achieve this result, a sufficient amount of boron carbide should be present in the inner core. Preferably, at leapt about 35% by weight of the inner core should consist of boron carbide to achieve verylow oxide formation. However, this; benefit accruen on a sliding scale - the more boron carbide used the better the result, but at the expense of displacing chrome carbide eind its beneficial effects. In addition to preventing oxiclst formation, the boron carbide 6 also lowers the melting temperature of the binder material (except for aluminum, which already has a low molting point) and improves the properties of the metal matrix making up the deposited coating. This gives fusing and self-fluxing properties to the coating. Furthemore, there is an increase in the temperature range of the liquid phase (i.e./ during melting or freezing). The increased range improves the spray and also improves the fusing characteristics. In addition to the qualities described above, the coatings of the present invention are to install and maintain. The boron additions in the metal binder matrix and the chromes carbide hard-phase morphology make repairs to the coatings relatively easy. Added to this, the high bond strength and the low coating residual allow existing coatings to be grit blasted without diabonding the surrounding material. While the inner coro formulation of the prasent invention centers around chrome carbide and boror carbide the inner core contain additional materials, additional may includes carbides, such ae tungsten carbide, titanium carbide, vanadium carbide, and the like; oxides, such ao aluminum oxide, chronic oxide, zirconium oxide, raid and boridcn, such as clii'orae boride, nickel borido., iron, boride, and the liko. The inner core may also ir.clude additional metiil , such as alxuninum, nickel, chrome, or alloy powder, or e powders, such as tungsten carbide nickel arid chrome carbide tucke.1 chrome . The of the chromium carbide and boron carbide will have an effect on the physical properties of the applied coating. Generally, the finer the grains of the , the more homogenous the coating will be and generally the better the wear and corrosion properties. However, the cost and manufacturing constraints will limit the lower end of the grain size range. U.S. Patent No. 4,741,971 (Longor et al.), the disclosure of which is hereby incorporated by reference, discloses thct effect of grain size with to boron carbide. EXAMPLES A composite wires of the present invention was formed with an outer sheath comprising of alloy 625 and an inner core comprising a substantially equivalent mixture of chromes carbide and boron carbide, INCONEL alloy 625 is a product of the Special Metals Corporation and contain 0,3.% C/ 0,51- Mn, 5.00 Fe, 0.02 P, 0.0151- S/ 0.5% Si, 0.5-1 Cu, 58% min Ki, 0,4% Al, 0.41 Ti, 20.0% -23.0% Cr, 3,15-4.15% Nb+Ta, 8,0%10,0% Mo. This composite wire provided coatings with good toughness characteristics, low oxicleo, and good woar due to the novel carbide formulation of the inner core. In addition, there was an increase in the hardnese of the metal binder due to the boron content The coatings also exhibited good bonding characteristics. The following table illustrates the improved wear resistant of a coatings deposited by a composite wire of the present invention (row 3 and row 4] compared to the wear ce of other coatings; ASTM G6S Wear Test (1S minutes): Coatings Height Lose (grams lost:/6QOO wheel 1) Bc Cr B (Arc) 0.429 2) pe Cr No Mn B (HVOF) 0.319 3) CrC/BC - Alloy 625 (Arc) 0,285 4) CrC/BC - Fe Cr (rc) 0.212 After PuDJpqf 3} CrC/BC - Alloy 6?,5 (Arc) 0.184 4) CrC/BC - Pe Cr (Arc) 0,165 Note that coatings of the present invention, as above/ have low oxide content and thus have superior fusing chracteristics. The wear resistances of the CrC/BC - Alloy 625 coating and the CrC/BC - Fa Cr coating were subtantially improved upon fusing, In addition to the improvement to wear resistance, the overall strength of the metal binder was also substantially increased. The coating deposited with the Alloy 625 composite wire exhibited an average hardness measurement of 003.2 100 g/Vickcrs/10 seconds. whereas, coatings of pure alloy 62S are typically on the order of 280-350 3,00 g/Vickers/10 seconds. To illustrate bond strength , clean, bright smooth steel coupons were coated, without any surface roughness, to establish how thick a coating could be sprayed before spalling occurred {i,e., bond failure). The first coupon was are sprayed with pure alloy 625 and the second coupon was sprayed with a composite wire comprising an alloy 625 outer sheath and an inner core comprising 40% by weight boron carbide arid 60% by weight chromium carbide. The first coupon exhibited delamination at 300 whereas the coating applied in accordance with the present invention way sprayed up to 2000 um without any appearance of spalling. Example 3: Two clean steel coupons were coated, with grit-blasted surfaces; the first with pure alloy 625 and the second with a composite wire comprising an alloy 625 outer sheath and an inner core comprising 400 by weight boron carbide and 60% by weight chromium carbide. The coupons were necnanically damaged by cracking off the coating with a hammer and chisel. The pure 625 coating was peeled off of the first coupon as a continuous layer, while the composite wire sprayed coating could not be disjoined from the coupon. Rather, the composite wire sprayed coupon only sustained damage to the impact site thus illustrating the high bond strength. As stated above, in addition to good toughneas, wear resistance, increased metal blinder hardness, and improved bonding of Che coating to the substrate, the inner core formulation, of the present invention also inhibits oxide formation. This characteristic of the boron carbide/chrome carbide formulation is illustrated in Figures l and 2. Figure .1 shows a cross-sectional electron micrograph of a coating sprayed with pure alloy 62S. The coating exhibits high oxide content, which shows up in the micrograph as grey bands. Due to the high oxide content, the alloy 635 coating will not fuse or melt as alloy 625 would fuse or melit if it were oxide free. Conversely, as can be sesn in Figure 2, the coating sprayed with an alloy 62S/boron carbide-chrome carbide composite wire exhibits far less oxide content and can be easily remeltod and fused. While- alloy 625 in a preferred alloy for the outer sheath in ccrcain high tempearature erosion-corrosion Applications, alternative metals and alloy can alscs be employed. For examples, alternative chrome bearing nickel baao alloys include alloy C- 276, alloy 586, or alloy 59Q. INCONEI/ C-276, alloy 68G, and alloy 6.90, which are all produced by the Special Metals Corporation contains: 0.021- C, 1.0% Mn, 4.0%-7vO% P&t 0.04% 2, 0.03% S, 0.08% Si, 0.5% Cu, bal. N.I, 2,5% Co, l4.16.5 Cr, 15.0%-17.0% Mo, 3.0%-4.5% W (JKCONEL C-27); 0.01% C, 1.0* Mn, 5.0% Fo, 0.02% P, 0.02% 8, 0.08% Si, 0.5% Cu, b a l . , O.S^ Al 0.2S% Ti, 19.0%23.0% Cr, 15,0%-17.C% Mo, 3.0%-4.4% W. (1NCONJ3L* alloy 686); and 0.02% C, 1,0% Mn, 7.0%-11.0% Pe, 0,015% S, 0.5% Si, 0.5% Cu, bal. Hi, 27%-31% Cr (INCONEL" alloy 690), Nickel copper allloys, such aa alloy 400, alloy R-405, and the like, and nickel molybdenum alloys much as, alloy B, alloy B-2, and the like, may also be employed depending en the required physical properties of the resulting coating and the environment to which t-he coating will be exposed. As stnted above, the metal, binder material is not limited to nickel base alloys?, rather the outer sheath way be constructed of any metal or alloy. Additional suitable binder material includes, but is not limited to, iron, carbon and low alloy steels, stainless steels, nickel, coppe.r, copper alloys (o.g./ brasses, bronzes, and aluminum bronazes), aluminum, aluminum alloys (e.g., aluminumcopper, nl aluminum-manganese, a aluminum-manganese -magaesium, aluminum- silicon, aluminum- manganese-magniesium-chrorme aluminumm - s i l i c o n , a n d a l u m i n u m - z i n c - c o p p e r ) , titanium, titanium alloys (e..g., titanium alloyed with palladium,: molybdenum, nickel, aluminum, vanadium, niobium, tantalum, tin, 55 ir con ium, chromium and iron), cobalt, cobalt alloys (c.ci,, cobalt alloyed with chromium, nickel, molybdenum and tungsten), zirconium, zirconium alloys, tantalum and tantalum alloys. The combination of any of thcae binders with the inner core powder ol the present invention moults in coatings having superior phyaical properties over conventional contings. The cored wires may be formed in a conventional manner by placing the mix of carbides, which need not be an agglomerated mix, onto an alloy 62,5 strip, or a strip o£ some other outer sheath alloy, which is drawn continuously through a plurality of wire drawing dics to form an outer wire sheath around an inner core. The final outer diameter of the cored wire will upon the application for which it is used. For most applications, the cored wire final diameter ranges between about 0.6 mm to about 6.4 mm. Conventional cored wire manufacturing techniques are discloaed in U.S, Patent Application MOM, 6,156,443 (Dallaire et al.) »nd 6,S13,72B (Hughea ct al.), of which both disclosures are hereby incorporated by reference. Although the present invention has been described in terms of specific embodiments, it io anticipated that alteration and modifications there of will no doubt become apparent to those skilled in the art. It is there fore intended that, the following claims be interpreted as covering all alterations modifications that fall within the truss spirit and scope of the We claim: 1. A composite wire for producing a wear resistant and corrosion resistant coating on a substrate, said composite wire consisting of a tubular metallic outer sheath encapsulating an inner core characterized in that the inner core is powdered and said inner core comprises a mixture of boron carbide of at least 35% by weight, and chrome carbide in an amount between 67% and 233% by weight of the amount of boron carbide. 2. The composite wire as claimed in claim 1, wherein the outer sheath is formed of an essentially pure metal. 3. The composite wire as claimed in claim 1, wherein the outer sheath is formed of an alloy comprising a base metal. 4. The composite wire as claimed in claim 3, wherein the base metal of the alloy is selected from the group consisting of iron, nickel, aluminum, molybdenum, tantalum, copper, and titanium. 5. The composite wire as claimed in claim 3, wherein the alloy is a nickel based alloy. 6. The composite wire as claimed in claim 5, wherein the nickel base alloy contains chromium. 7. The composite wire as claimed in claim 6, wherein the nickel base alloy contains at least 40 % by weight of nickel. 8. The composite wire as claimed in claim 7, wherein the nickel based alloy contains molybdenum. 9. The composite wire as claimed in claim 8, wherein the nickel based alloy is an alloy 625. 10. The composite wire as claimed in claim 1, wherein the inner core contains substantially equivalent amounts of chrome carbide and boron carbide. 11. A method of forming a wear resistant and corrosion resistant coating on a substrate comprising the steps of: providing a composite wire as claimed in any of claims 1-16 and employing the wire to form the coating on the substrate. 12. The method as claimed in claim 17, wherein the step of employing the wire to form the coating comprises thermally spraying the wires onto the substrate. 13. The method as claimed in claim 17, wherein the step of employing the wire to form the coating comprises spraying the wires onto the substrate and fusing the coating. 14. The method as claimed in claim 17, wherein the step of employing the wire to form the coating comprises depositing the wires onto the substrate by welding techniques. 15. The method as claimed in claim 17, wherein the outer sheath is formed of an essentially pure metal. 16. The method as claimed in claim 17, wherein the outer sheath is formed of an alloy comprisng a base metal. 17. The method as claimed in claim 22, wherein the base metal of the alloy is selected from the group consisting of iron, nickel, aluminum, molybdenum, tantalum, copper, and titanium. 18. The method as claimed in claim 22, wherein the alloy is a nickel base alloy. 19. The method as claimed in claim 24, wherein the nickel base alloy contains chromium. 20. The method as claimed in claim 25, wherein the nickel base alloy contains at least 40 % by weight of nickel. 21. The method as claimed in claim 26, wherein the nickel base alloy contains molybdenum. 22. The method as claimed in claim 27, wherein the nickel base alloy is an alloy 625. 23. A substrate having a coating formed in accordance with the method as claimed in any of claims 11-22.

Documents:

5540-DELNP-2005-Abstract-(26-12-2008).pdf

5540-delnp-2005-abstract.pdf

5540-delnp-2005-Assignment-(02-05-2011).pdf

5540-DELNP-2005-Claims-(14-01-2009).pdf

5540-DELNP-2005-Claims-(26-12-2008).pdf

5540-delnp-2005-claims.pdf

5540-delnp-2005-Correspondence-Others-(02-05-2011).pdf

5540-DELNP-2005-Correspondence-Others-(14-01-2009).pdf

5540-DELNP-2005-Correspondence-Others-(26-12-2008).pdf

5540-delnp-2005-correspondence-others.pdf

5540-DELNP-2005-Description (Complete)-(26-12-2008).pdf

5540-delnp-2005-description (complete).pdf

5540-DELNP-2005-Drawings-(26-12-2008).pdf

5540-delnp-2005-drawings.pdf

5540-delnp-2005-Form-1-(02-05-2011).pdf

5540-DELNP-2005-Form-1-(26-12-2008).pdf

5540-delnp-2005-form-1.pdf

5540-delnp-2005-form-13-(21-11-2006).pdf

5540-delnp-2005-form-13.pdf

5540-delnp-2005-Form-16-(02-05-2011).pdf

5540-delnp-2005-form-18.pdf

5540-delnp-2005-Form-2-(02-05-2011).pdf

5540-DELNP-2005-Form-2-(26-12-2008).pdf

5540-delnp-2005-form-2.pdf

5540-DELNP-2005-Form-3-(26-12-2008).pdf

5540-delnp-2005-form-3.pdf

5540-delnp-2005-form-5.pdf

5540-delnp-2005-GPA-(02-05-2011).pdf

5540-DELNP-2005-GPA-(26-12-2008).pdf

5540-delnp-2005-Petition Others-(15-05-2012).pdf