Patent Publication Number: US-2005136279-A1

Title: Chrome composite materials

Description:
TECHNICAL FIELD  
      This invention relates generally to chrome composite powders and, more specifically, to ferrochrome carbide/boride-nickel composite powders.  
     BACKGROUND  
      Wear and corrosion resistant materials are of great interest to many industries, including, but not limited to, the heavy machinery, automobile, and aerospace industries. Even as demand increases for complex machined components with long life/duty cycles, low maintenance requirements, and improved performance under harsh conditions, a parallel objective exists to achieve these ends at reduced cost to both the industry and the consumer. Achieving satisfactory wear and corrosion resistance in today&#39;s complex materials has typically required the use of relatively expensive starting/raw materials in combination with lengthy and complex processing techniques. While this route can produce wear and corrosion resistant materials, it can be costly.  
      For example, chrome carbide/boride types of powders are used in applications for wear and corrosion resistant coatings, as disclosed in U.S. Pat. No. 5,863,618. These chrome carbide/boride powders are formed by combining a chrome carbide material, such as Cr 3 C 2 , Cr 23 C 6 , or Cr 7 C 3 , which are typically high cost materials, with other materials including boron. The resulting chrome carbide/boride powders may be used to form wear and corrosion resistant coatings.  
      A disadvantage of using the chrome carbide to generate chrome carbide types of composite materials is the high cost of the precursor materials. For example, chrome carbide is expensive and is typically produced only on small scales for specialty applications. Moreover, due to the high melting point of the chrome carbide materials, powder deposition efficiency (i.e., a measure of how much of a material ends up in a coating) is low. Therefore, these chrome carbide composite materials are even more costly to apply.  
      The invention is directed to overcoming one or more of the problems or disadvantages existing in the prior art.  
     SUMMARY OF THE INVENTION  
      One aspect of the invention includes a method of making a composite carbide-boride powder. The method includes selecting a ferrochrome material, selecting a nickel-containing material, and selecting a boron-containing material. The ferrochrome material, the nickel-containing material, and the boron-containing material is combined together to form a mixture, and the composite carbide-boride powder is generated from the mixture.  
      A second aspect of the invention includes a composite powder that includes a ferrochrome component, a nickel-based component, and an iron-boride component.  
      A third aspect of the invention includes a composite powder. The composite powder includes a plurality of particles, and at least some of the particles include a matrix material including of at least one of nickel and nickel-chromium. A plurality of Fe—Cr-boride particles is dispersed in the matrix material. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a scanning electron microscope (SEM) micrograph illustrating representative morphology of a composite powder consistent with an exemplary embodiment of the invention.  
       FIG. 2  is an SEM micrograph illustrating representative morphology of an as-sintered composite powder consistent with an exemplary embodiment of the invention.  
    
    
     DETAILED DESCRIPTION  
      A method of making a composite carbide-boride powder is provided. The method may include selecting a ferrochrome material, a nickel-containing material, and a boron-containing material, and mixing the ferrochrome material together with the nickel-containing material and the boron-containing material. The ferrochrome material can be selected from among many materials that include at least some iron, chromium, and/or carbon. For example, in one embodiment, the ferrochrome material may include at least one of (CrFe) 7 C 3  and (CrFe) 3 C 2 , which can be obtained from many industrial and steel making material vendors, including FW Winter, Shieldalloy, Chemalloy, among others. Further, the ferrochrome material may be selected in powder form, ingot form, or any other form suitable for obtaining the ferrochrome precursor material. Similarly, the nickel-containing material and the boron-containing material may be provided in powder form, ingot form, or any other suitable form. The nickel-containing material may be selected from a variety of compounds that may serve as a source of nickel. In one exemplary embodiment, the nickel-containing compound includes substantially pure nickel (i.e., nickel metal of at least about 90% purity). The boron-containing material can be selected from among many materials that include at least some boron. In certain embodiments the boron-containing material may include iron and may be characterized as a ferroboron material.  
      The ferrochrome material, the nickel-containing material, and the boron-containing material may be mixed in a variety of ways. For example, these materials, especially when in powder form, may be mixed together with a solvent to form a slurry. Alternatively, these materials may be melted together to form a melt. The disclosed composite carbide-boride powders, ultimately, may be generated from the mixture of the ferrochrome material, the nickel-containing material, and the boron-containing material. Various methods for generating the composite carbide-boride powders may be used including, for example, spray drying and sintering, atomization, gas atomization, sintering and crushing, chemical vapor deposition, and cladding.  
      Various additional materials may be added to the mixture of the ferrochrome material, the nickel-containing material, and the boron-containing material. For example, a carbon-containing material (e.g., activated carbon, graphite, or any other suitable source of graphite) may be added to the mixture. Supplemental chromium may also be added to the mixture. Similarly, in some embodiments, one or more of silicon, titanium, niobium, vanadium, tantalum, molybdenum, tungsten, and manganese may be added. For certain applications, any one of these materials may be limited to no more than 5% by weight of the composite carbide-boride powder.  
      The disclosed composite carbide-boride powders may have a variety of particle sizes. In one embodiment, an average particle size of the composite carbon-boride powder may be from about 3 μm to about 500 μm. In still other embodiments, the average particle size may be from about 10 μm to about 60 μm.  
      The weight percentages of the constituents of the ferrochrome material may vary according to the requirements of a particular application. For example, the selected ferrochrome material may include carbon up to about 14 percent by weight. Further, the ferrochrome material may contain iron up to about 65 percent by weight. In certain embodiments, however, the amount of iron may be limited to less than about 35 percent by weight. The amount of chromium in the ferrochrome material may also vary between about 15 percent by weight and about 75 percent by weight. Further, the ferrochrome material may have a iron to chromium weight ratio of from about 0.2 to 0.5 by weight and a carbon to chromium ratio of from about 0 to 0.2 by weight. In certain embodiments, the boron-containing material (e.g., an iron-boride or nickel boron material) may have a boron content up to about 19 percent by weight.  
      Similarly, the weight percentages of the constituents of the composite carbon-boride powder may also be varied according to the requirements of a particular application. For example, the composite carbon-boride powder may include carbon up to about 14 percent by weight. Further, the composite carbon-boride powder may contain iron up to about 65 percent by weight. In certain embodiments, however, the amount of iron may be limited to less than about 35 percent by weight. The amount of chromium in the composite carbon-boride powder may also vary between about 15 percent by weight and about 75 percent by weight. The composite carbon-boride powder may also include up to about 35 percent by weight of nickel and up to about 19 percent by weight of boron.  
      The weight percentages of these constituents may be adjusted depending on a particular application. In one exemplary embodiment, the iron may be included in the composite carbide-boride powder in an amount of between about 10 weight percent to about 55 weight percent. Further, the amount of boron may be limited to 12 weight percent or less. A balance between hardness and toughness of the composite material may be obtained, for example, with a carbon content of up to about 10 weight percent and a boron content up to about 8 weight percent.  
      In one exemplary embodiment, the composite carbide powder may be made by melting together the various materials in ingot form. For example, a high carbon ferrochrome powder ingot, nickel ingot, chromium ingot, and a ferroboron ingot may be melted together. The ferroboron ingot may have a boron content of about 14 percent to about 20 percent boron by weight. The materials may be combined, for example, during a melting process, which provides molten material. The combined melt may be heated to about 1550° C. to about 1700° C., and a composite carbide-boride powder may be generated from the melt.  
      As noted above, the disclosed composite carbide-boride powders may be produced using various techniques. One such technique includes atomization. Atomization techniques may be used to make a fine spray of droplets from a liquid source (e.g., molten metal, liquid slurry, etc.) Molten metal, for example, may be integrated (e.g., by injection) into a high pressure directed fluid stream of gas, water, or air, for example, to produce particles of varying size (usually from about 10 μm to about 150 μm in diameter), size distribution, shape, composition, and microstructure. Droplets carried by the gas, water, or air may be solidified and collected in a container, which may be filled with an inert gas to prevent any undesired reactions (e.g., oxidization) with the particles.  
      Generating composite carbide/boride powders through atomization can form a chrome carbide-boride structure in each atomized particle. These chrome carbide-boride structures may be dispersed within a matrix material. In one embodiment, the matrix material may include a FeCrNi(BC) solid solution. In other embodiments, the matrix material may any one or more of a nickel, nickel-chromium, or iron-based matrix The chrome carbide-boride structures may include particles of Fe—Cr-borides, carbide-borides, and any combination thereof.  FIG. 1 , for example, is a SEM micrograph illustrating representative morphology of a gas atomized chrome iron nickel carbon boron powder consistent with an exemplary embodiment of the invention. A distribution of spheroid particles  10  with particle diameters of about 20 μm is visible in  FIG. 1 .  
      The composite carbide-boride powders may also be generated by other techniques, including spray drying and sintering. In spray drying and sintering, the powder particles may be produced from a slurry. Spray drying is a process that transforms a slurry liquid into a powder by spraying the slurry into a heated environment. When the slurry enters the heated environment, the liquid portion of the slurry is vaporized, which leaves behind the solid particles of the powder. Spray drying can be used to produce dense, non-hollow particles with a controlled size distribution. While optional, the spray dried powder may be sintered at an elevated temperature (e.g. about 1000° C. to about 1280° C., depending on a particular composition), to form a loosely bonded powder body. After sintering, this powder body can be broken and sieved to form the composite carbide-boride powder.  
      Sintering and crushing may also be used to produce the composite carbide-boride powders. Sintering of the powder may serve to densify the powder by, for example, forming metallurgical bonds between individual particles and by facilitating chemical reactions for forming the composite carbide-boride powders. Sintering may be carried out in a batch furnace or push furnace in a reducing atmosphere.  FIG. 2 , for example, is an SEM micrograph illustrating representative morphology of as-sintered and crushed chrome iron boron powder particles consistent with an exemplary embodiment of the invention. As-sintered and crushed particles  12 ,  14 , and  16  exhibit a rough, irregular surface and sub-100 μm dimensions.  
      Prior to generating the composite carbide-boride powders, approximately 1% to approximately 2% activated carbon, graphite, or other carbon-containing powder (e.g. a carbonaceous material) may optionally be added to a mixture of the constituent materials used to form the composite carbide-boride powders. The presence of this activated carbon may promote conversion of a (CrFe) 7 C 3  phase to a higher hardness (CrFe) 3 C 2  phase. Specifically, the approximately 1% to approximately 2% activated carbon, graphite, or other carbon-containing powder may combine with chrome or other metals during powder particle preparation to form a carbide structure in the final composite carbide-boride powder.  
      As noted above, the disclosed composite carbide-boride powders may include particles dispersed in a matrix material. Particularly, in one embodiment, at least a majority of the particles in the composite carbide-boride powder may include Fe—Cr-carbide-boride particles dispersed within at least one of a nickel, nickel-chromium, or iron-based matrix. To make this structure, a metal may be mixed with a high carbon ferrochrome material prior to spray drying, or added to the melt prior to atomization, depending on the technique used. The structure may be formed when the combination of the metal and ferrochrome material is spray dried or atomized and sprayed. For example, if a metal powder (e.g. nickel (Ni) or chromium (Cr)) is mixed with the high carbon ferrochrome powder in the melt, a structure may be produced when the melt is atomized and sprayed. This structure may include hard Fe—Cr-carbide-boride particles dispersed relatively uniformly in a softer, tougher Ni matrix.  
      The disclosed composite carbide-boride powders may be used to form various composite materials for use in many applications. For example, these composite materials may be used to form stand-alone parts, composite coatings, etc. The composite materials, like the composite powders from which they may be derived, may include a high carbon ferrochrome material combined with a nickel-based material and an iron-boride material. In the composite materials, the ferrochrome component and the iron-boride component may be dispersed in the nickel-based material, for example. That is, Fe—Cr-carbide boride particles may be dispersed in a nickel-based or nickel-iron based matrix. Alternatively, however, the dispersal of the ferrochrome and iron-boride components in the nickel-based material may provide a composite material in which at least some portions of the material constitute an alloy of any combination of nickel, chrome, iron, carbon, and/or boron.  
      The weight percentages of the constituents of the composite materials may depend from the weight percentages of the constituents of the composite powder materials used to form the composite materials. The composite material may have a carbon component in an amount up to about 14 weight percent and a chrome content of up to about 65 percent by weight. Iron may be included in an amount of up to about 65 percent by weight, and silicon may be included in an amount of less than about 5 percent by weight. Nickel may represent up to about 40 weight percent and boron may represent up to about 19 weight percent of the composite material.  
      Coatings and/or free standing parts using the disclosed composite carbide-boride powders can be made in a variety of ways. Further, coatings made from the disclosed carbide-boride composite powders may be applied to a variety of objects/substrates (e.g. a carbon steel). For example, powders may be used to form coatings on substrates with any of a variety of application methods including thermal spray processes (e.g., plasma spray, flame spray, HVOF, HVAF, detonation gun spray, and cold spray), laser cladding, plasma welding (e.g., PTA), and sintering (e.g., as associated with one or more powder metallurgy processes).  
     INDUSTRIAL APPLICABILITY  
     EXAMPLE  
      In one exemplary embodiment of the invention, a melt was formed by heating together a high carbon ferrochrome ingot (e.g., about 35 percent by weight of the melt), a Cr ingot (e.g., about 30 percent by weight of the melt), a Ni ingot (e.g., about 15 percent by weight of the melt), and a ferroboron ingot (e.g., about 19 percent by weight of the melt) in an induction crucible. The high carbon ferrochrome ingot contained about 9 percent by weight C, about 64 percent by weight Cr, and about 27 percent by weight Fe. About 1 percent by weight silicon was added to the melt. This melt was heated to form a mixture of about 35 percent by weight high carbon ferrochrome, about 30 percent by weight chromium, about 15 percent by weight nickel, and about 19 percent by weight ferroboron in solution. This combination was heated to about 1550° C. to about 1700° C., and the melt was gas atomized. A dendrite chrome carbide-boride structure was formed in each atomized particle, which was part of an FeCrNi(BC) solid solution. A coating was made using these atomized particles and a Metco Diamond Jet System, which achieved coating hardness between about 940 to about 1200 (knoop, 100 gram load).  
      The disclosed high carbon ferrochrome precursor materials and boron-containing powders may be used to produce composite carbide-boride powders for applications including coating of engine parts, cylinders, rods, bearings, joints, cam shafts, axles, etc. Use of these low cost precursors may translate into significant cost reduction over existing materials and methods. In fact, based on the cost of the precursor materials, powders produced using carbon ferrochrome precursors may cost less than half as much as powders and coatings produced using known materials and methods. Furthermore, the boron derived from the use of ferroboron powders, for example, can provide powder and coating hardness values comparable to when boron alone is used. Ferroboron, however, may be obtained at a fraction of the cost of boron. Despite the lower cost, coatings made using the disclosed composite powders may offer similar or better wear and corrosion resistant properties as the existing materials. These composite carbide-boride powders may be used in any industry where wear and corrosion resistant properties are desired.  
      It will be apparent to those skilled in the art that various modifications and variations can be made in the described powders, coatings, and methods of making powders and coatings, without departing from the scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.