Hardfacing Containing Tungsten Carbide Particles with Barrier Coating and Methods of Making the Same
20180178283 ยท 2018-06-28
Inventors
Cpc classification
B22F2999/00
PERFORMING OPERATIONS; TRANSPORTING
B22F2301/205
PERFORMING OPERATIONS; TRANSPORTING
B22F2999/00
PERFORMING OPERATIONS; TRANSPORTING
B22F1/17
PERFORMING OPERATIONS; TRANSPORTING
C04B35/62897
CHEMISTRY; METALLURGY
B22F1/17
PERFORMING OPERATIONS; TRANSPORTING
C04B2235/5436
CHEMISTRY; METALLURGY
International classification
B23K35/02
PERFORMING OPERATIONS; TRANSPORTING
C04B35/628
CHEMISTRY; METALLURGY
Abstract
A hardfacing composition comprising tungsten carbide particles having a barrier coating and a binder alloy is disclosed. The tungsten carbide particles comprise at least one kind of cast tungsten carbide, carburized tungsten carbide, macro-crystalline tungsten carbide, or sintered tungsten carbide. The barrier coating comprises at least one of metallic carbides, borides, nitrides, or their hybrid compounds. The hardfacing composition takes one of the forms selected from a welding/brazing tube, rod, rope, powder, paste, slurry, or cloth, which are suitable for being applied by various welding or brazing methods. The barrier coating would prevent or mitigate the degradation of the tungsten carbide particles due to attack of a molten binder alloy during a welding or brazing process. One of thermoreactive deposition/diffusion methodshalide activated pack cementation for making tungsten carbide particles having a barrier coating is disclosed.
Claims
1. A hardfacing composition comprising: a carbide phase comprising tungsten carbide particles having a barrier coating disposed thereon; and a binder alloy, wherein the tungsten carbide particles comprise at least one of cast tungsten carbide, carburized tungsten carbide including carburized cast tungsten carbide, macro-crystalline tungsten carbide, or sintered tungsten carbide with ferrous metals of cobalt, nickel, iron, or alloys thereof as binders or binderless; and wherein the barrier coating comprises at least one of metallic carbides, borides, nitrides, or their hybrid compounds, whereby degeneration of the carbide phase can be prevented or mitigated during a hardfacing process.
2. The hardfacing composition as defined in claim 1, wherein the tungsten carbide particles have a size larger than 20 m.
3. The hardfacing composition as defined in claim 1, wherein the barrier coating has a thickness larger than 0.5 m.
4. The hardfacing composition as defined in claim 1, wherein the barrier coating comprises at least one of metallic carbides, borides, nitrides, or their hybrid compounds of the metals selected from titanium, niobium, zirconium, vanadium, tantalum, hafnium, chromium, or aluminum.
5. The hardfacing composition as defined in claim 1, wherein the barrier coating has multiple layers; and wherein at least one layer is the metallic carbides, borides, nitrides, or their hybrid compounds.
6. The hardfacing composition as defined in claim 1, wherein the barrier coating is made by one of the methods selected from chemical vapor deposition, physical vapor deposition, or thermoreactive deposition/diffusion.
7. The hardfacing composition as defined in claim 1, wherein the hardfacing composition is in one of forms selected from a welding or brazing tube, rod, rope, powder, paste, slurry, or cloth.
8. The hardfacing composition as defined in claims 1 and 7, wherein the hardfacing process is a welding or brazing method selected from electric arc, oxyacetylene torch, laser cladding, plasma transferred arc, furnace heating, or induction heating.
9. Method for making tungsten carbide particles having a barrier coating, comprising halide activated pack cementation, wherein the tungsten carbide particles comprise at least one of cast tungsten carbide, carburized tungsten carbide including carburized cast tungsten carbide, macro-crystalline tungsten carbide, or sintered tungsten carbide with ferrous metals of cobalt, nickel, iron, or alloys thereof as binders or binderless; wherein the barrier coating comprises at least one of metallic carbides, borides, nitrides, or their hybrid compounds; and wherein the pack cementation includes heating a mixture of metal/alloy powders, halide powders, and the tungsten carbide particles in a sealed container to a predetermined temperature, keeping the sealed container at the predetermined temperature for a predetermined period of time, and then recovering the tungsten carbide particles by crushing and screening.
10. The method as defined in claim 9, wherein the halide is ammonium chloride.
11. The method as defined in claim 9, wherein the metal/alloy is selected from titanium, niobium, zirconium, vanadium, tantalum, hafnium, chromium, or their alloys.
12. The method as defined in claim 9, wherein the predetermined temperature is between 750 C. and 1250 C.; and wherein the predetermined time is between 0.5 hours and 12 hours.
13. The method as defined in claim 9, wherein the tungsten carbide particles are subject to one of chemical heat treatments of carburizing, carbonitriding, boriding, or nitriding, before and/or after the pack cementation deposition.
14. The method as defined in claim 9, wherein the barrier coating has multiple layers; and wherein at least one layer is selected from the metallic carbides, borides, nitrides, or their hybrid compounds.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0018]
[0019]
[0020]
[0021]
[0022]
DRAWINGREFERENCE NUMERALS
[0023] 10 tungsten carbide; [0024] 12 coating layer of metallic carbides, borides, nitrides, or their hybrid compounds; [0025] 20 coating layer of ceramics, metals, or alloys; and, [0026] 30 coating layer of metals or alloys.
DETAILED DESCRIPTION OF THE INVENTION
[0027] Embodiments of the disclosure relate to providing a hardfacing composition comprising tungsten carbide particles having a barrier coating disposed thereon, and a binder alloy. The hardfacing composition has at least 30 wt. % of the coated tungsten carbide particles. The tungsten carbide particles are selected from at least one type of cast tungsten carbide, carburized tungsten carbide, macro-crystalline tungsten carbide, or sintered tungsten carbide. The barrier coating comprises at least one of metallic carbides, borides, nitrides, or hybrid compounds thereof.
[0028] Carburized tungsten carbide is a product of solid-state diffusion of carbon into tungsten metal particles or powders at high temperatures in a protective atmosphere. Usually, it is polycrystalline monotungsten carbide (WC). In this disclosure, the carburized tungsten carbide also comprises a cast tungsten carbide that is subject to carburizing. Cast tungsten carbide is a eutectic phase of WC and W.sub.2C. Carburization transforms W.sub.2C into WC at least around the surface layer of the cast tungsten carbide. In a molten metal pool during welding or brazing, WC is more thermodynamically stable than W.sub.2C. The carburization would improve the thermodynamic stability of the cast tungsten carbide.
[0029] In some embodiments of this disclosure, the sintered tungsten carbide particles are tungsten carbide cemented with cobalt, nickel, iron, or their alloys. The sintered tungsten carbide particles also may be binderless, that is, free of any metallic binders.
[0030] In some embodiments of this disclosure, the tungsten carbide particles have a size larger than 20 m. They are in a spherical or angular (crushed) shape.
[0031] In some embodiments of this disclosure, the coatings on tungsten carbide particles consist of at least one of metallic carbides, borides, nitrides, or their hybrid compounds. The metallic carbides are the carbides of the metals selected from titanium (Ti), niobium (Nb), zirconium (Zr), vanadium (V), tantalum (Ta), hafnium (Hf), or chromium (Cr), that is, TiC, NbC, ZrC, VC, TaC, HfC, or Cr.sub.3C.sub.2. The metallic borides are the borides of the metals selected from Ti, Nb, Zr, V, Ta, Hf, or Cr, that is, TiB.sub.2, NbB.sub.2, ZrB.sub.2, VB.sub.2, TaB.sub.2, HfB.sub.2, or CrB. The metallic nitrides are the nitrides of the metals selected from Ti, Nb, Zr, V, Ta, Hf, Cr, or Al (aluminum), that is, TiN, NbN, ZrN, VN, TaN, HfN, CrN, or AlN. The hybrid compounds are carbides, carbonitrides, borides, or nitrides that contain more than two comprising elements, but at least one metallic element selected from Ti, Nb, Zr, V, Ta, Hf, Cr, or Al. For example, they may be titanium carbonitride [Ti(CN)], titanium aluminum nitride [(TiAl)N], titanium tungsten carbide [(TiW)C], or titanium tungsten carbonitride [(TiW)(CN)], etc.
[0032] These carbides, borides, nitrides, and their hybrid compounds are thermodynamically stable and their reactions with a metal melt are much smaller than those of the tungsten carbide with the metal melt. Their dissolution rates in the metal melt are lower than those of the tungsten carbide. They can prevent or mitigate the dissolution of the tungsten carbide during welding or brazing operations. Another reason for selecting these compounds as a barrier coating material is that they are not completely insoluble like oxides, but do have a limited solubility in the metal melt and, thus, they can be wetted well by the metal melt. Furthermore, the interface between these compounds and a binder alloy is coherent or semi-coherent and consequently, the bonding between the coated tungsten carbide particles and the binder is metallurgical and strong. Considering that the compounds are soluble in the metal melt, the coating compounds must have a certain amount of thickness. In this disclosure, a coating has a thickness larger than 0.5 m, rather than in a nanometer range, so as to keep their effectiveness. During welding or brazing processes, the dissolution of such the coating materials on the tungsten carbide particles would release small amount of elements into the binder and the released elements would alloy the binder matrix. The minor alloying would not degrade the properties of the binder material, but it would rather improve the properties. In fact, the metallic elements selected in the coating compounds in the disclosure are commonly used micro-alloying elements in steels. For example, Ti, Zr, Nb, V, Ta, and Hf are the important constituents in microalloyed steels and they can refine grain structures and generate fine precipitates.
[0033] One embodiment of this disclosure is a tungsten carbide particle having a single layer coating.
[0034] Another embodiment of the disclosure is a tungsten carbide particle having a multiple layer coating, wherein an outermost layer coating is selected from the metallic carbides, borides, nitrides, or their hybrid compounds, such as those discussed above.
[0035] Another embodiment of the disclosure is a tungsten carbide particle having a multiple layer coating, wherein an outermost layer is one of metals or alloys.
[0036] In this disclosure, the coatings on tungsten carbide particles aim to prevent or mitigate the dissolution of the tungsten carbide during welding or brazing operations. Partial or even complete dissolution of the coatings may occur during welding or brazing operations, which is dependent on welding or brazing processes. Even though they dissolve completely, the coatings must prevent or mitigate the degeneration of the tungsten carbide particles as reinforcements in a hardfacing layer, because the selected coating compounds have higher thermodynamic stabilities and lower dissolution rates than those of the tungsten carbide particles themselves.
[0037] In this disclosure, coatings on tungsten carbide particles can not only prevent or mitigate the degeneration of the tungsten carbide particles, but also can generate a compatible interface with a binder, which would benefit the bonding between the coated tungsten carbide particles and the binder in a hardfacing layer.
[0038] Some embodiments of the present disclosure relate to methods of making the coatings on tungsten carbide particles. The methods comprise CVD, PVD, TD, or any other suitable deposition techniques. During CVD or PVD processes, the tungsten carbide particles need to keep motion, so as to coat the particles uniformly, which can be achieved by a fluidized bed, a shaker, a trembler, etc. In fact, fluidized bed CVD or PVD techniques are industrially available for coating particles and powders, which can produce a uniform coating on the particles and powders. For example, U.S. Pat. No. 5,876,793 discloses recirculating fast fluidized bed CVD technique and equipment for coating tungsten carbide powder. TD techniques are commercially available for coating bulk metal components. TD techniques mainly include salt bath immersion coating and pack cementation. TD processing may be used to form a metallic carbide, carbonitride, boride, or nitride coating on tungsten carbide particles. For example, U.S. Appl. Pat. No. 2006/0,081,681 A1 teaches coating diamond grits with a metallic carbide using TDpack cementation method. Other deposition techniques can be employed, if desired.
[0039] TD techniques are thermoreactive deposition processes of a strong carbide-, boride- or nitride-forming element on surface of a substrate containing carbon, boron, or nitrogen to produce a carbide, carbonitride, boride, or nitride layer of that element. With the author's best knowledge, TD techniques have not been used for coating tungsten carbide particles. TD techniques require that a surface of a substrate has a certain amount of carbon, boron, or nitrogen. Therefore, if needed, a thermal diffusion, i.e. carburization, carbonitriding, boriding, or nitriding may be applied to tungsten carbide particles prior to TD processes to enhance the content of carbon, boron, or nitrogen around the surfaces of the tungsten carbide particles. In some cases, TD techniques may generate a multiple layer coating on tungsten carbide particles. An inner coating layer is either carbide, carbonitride, boride, or nitride, and an outer coating layer is either metals or alloys. These coatings that are formed by TD can be further carburized, carbonitrided, borided, or nitrided, if an outmost coating layer of metallic carbide, boride, nitride, or their hybrid compound is expected, respectively.
[0040] One embodiment of the present disclosure relates to halide activated pack cementation method of making coatings on tungsten carbide particles. In the halide activated pack cementation, carbide-forming metal powders, halide powders such as ammonium chloride, and tungsten carbide particles are mixed completely. Then, the powder mixture is loaded inside a container and the container is sealed. The container is heated to a predetermined temperature and held for a predetermined period of time. Generally, a holding temperature is between 750 C. and 1250 C. and a holding time is between 0.5 hours and 12 hours. The parameters of temperature and time are dependent on an expected coating thickness, a type of coating, as well as a type of tungsten carbide. During holding at an elevated temperature, the carbide-forming metals react with gaseous halide that volatilizes, and form a gaseous metal halide. The gaseous metal halide is transported onto the surfaces of the tungsten carbide particles. The gaseous metal halide further reacts with hydrogen gas and generate the carbide-forming metal atoms. These carbide-forming metal atoms deposit onto the surfaces of the tungsten carbide particles. The chemical reactions between the carbide-forming metal atoms and the carbon atoms result in the formation of carbide on the surfaces of the tungsten carbide particles as a coating layer.
[0041] Another embodiment of the present disclosure relates to pack cementation method of making coatings on tungsten carbide particles. The tungsten carbide particle is carburized prior to the pack cementation process, to enrich the carbon contents around the surface layers of the tungsten carbide particles. The carburization of the tungsten carbide can avoid or mitigate formation of the brittle eta phase (M.sub.6C) that has lower carbon content. If a carbonitride, boride, or nitride coating is expected, the tungsten carbide particles need to be subject to a chemical heat treatmentcarbonitriding/nitriding, boriding, or nitriding prior to the pack cementation process, to enrich the carbon/nitrogen, boron, or nitrogen contents around the surface layers of the tungsten carbide particles, respectively.
[0042] TDhalide activated pack cementation have some advantages in coating particles over CVD or PVD. TD technique is industrially available for coating bulk materials. Its equipment and materials for coating tungsten carbide particles are cost effective.
[0043] Tungsten carbide particles act as main reinforcements in hardfacing that are bonded in a binder alloy. The coated tungsten carbide particles are comprised in welding or brazing materials for hardfacing on metallic article surfaces. The welding or brazing materials can be in a form of only coated tungsten carbide particles/powders, premixed powders of coated tungsten carbide particles and binder materials, rods, tubes, ropes, brazing pastes, or cloths in that the coated tungsten carbide particles are premixed or pre-loaded with a binder material. After welding or brazing, the coated tungsten carbide reinforcing MMC hardfacings form on the article surfaces. The surfaces of the tungsten carbide particles are modified with the coatings to avoid or mitigate the degeneration of the tungsten carbide particles during welding or brazing processes. The welding and brazing processes include electric arc welding, oxyacetylene welding or brazing, induction welding or brazing, PTA welding, laser cladding, furnace brazing, etc.
[0044] For arc welding including electric arc and PTA, the coated tungsten carbide particles may be dropped through a feeding hopper in some embodiments into a molten metal pool on an article surface that is generated by arc. Electrode material may act as a binder such as for gas metal arc welding (GMAW). The coated tungsten carbide particles are entrapped into a hardfacing layer during welding. Alternatively, the coated tungsten carbide particles may be filled into a continuous metal/alloy tube such as a steel tube to form a welding tube. The welding tube may comprise the coated tungsten carbide particles with or without some additives such as alloying elements and other hard granules such as diamond or cubic boron nitride. The metal tube material itself may act as a binder of hardfacing. The welding tube may be fed into a molten metal pool generated by arc on an article surface to form hardfacing layers with embedded coated carbide as reinforcements.
[0045] For spray & fuse, PTA, or laser cladding, the coated tungsten carbide particles with binder material powders may be fed through a feeding nozzle onto an article surface and melted by a heating source such as oxyacetylene flame for spray & fuse, plasma arc for PTA, or laser beam for laser cladding. The coated tungsten carbide particles and binder powders may be fed using different nozzles. More commonly, the coated tungsten carbide particles are pre-mixed with binder powders to form a powder mixture as a feeding material for hardfacing. After solidification, a hardfacing layer forms with embedded coated tungsten carbide as reinforcements.
[0046] For oxyacetylene welding/brazing or gas tungsten arc welding (GTAW) with a rod, the coated tungsten carbide particles may be filled into a metal rod such as a steel rod to produce a welding or brazing rod. The welding or brazing rod may comprise some additives such as alloying elements and deoxidizer. The metal rod material acts as a binder of hardfacing. The welding or brazing rod may be melted by oxyacetylene flame or arc, and deposited onto an article surface. A hardfacing layer with embedded coated tungsten carbide as reinforcements forms.
[0047] For oxyacetylene welding or brazing with a rope, the coated tungsten particles may be mixed with alloying elements, deoxidizer, and resin to form a thick coating on a flexible rope with a metal core. The metal core acts as a binder of hardfacing after deposition. The rope may be melted by oxyacetylene flame and deposited onto an article surface. A hardfacing layer forms with embedded coated tungsten carbide particles as reinforcements.
[0048] For furnace brazing, the coated tungsten carbide particles may be put into brazing pastes or cloths with mixing with binder materials and some additives such as flux. The pastes or cloths are put onto an article surface to form a green hardfacing compact. Then, the whole article is put into a furnace for brazing. The furnace is heated to a predetermined brazing temperature (above melting point of a binder material) and held for a predetermined period of time. Cooling may be in the furnace or in air. A hardfacing layer forms with embedded coated tungsten carbide particles as reinforcements. Alternatively, induction heating or oxyacetylene flame may be used for brazing.
Example 1: TDHalide Activated Pack Cementation
[0049] Tungsten carbide particles to be coated are 100 g spherical cast tungsten carbide having a size of 45-150 m. The depositing reactive materials consist of 20 g Ti powders and 12 g ammonium chloride (NH.sub.4Cl). NH.sub.4Cl powders are baked around 120 C. for 1 hour before use. All the materials including the tungsten carbide particles, Ti powders, and NH.sub.4Cl powders are mixed completely in a ball mill for 4 hours. The mixed powders are loaded inside a stainless steel container with a lid and the container is sealed with alumina paste. An electric resistance furnace with flowing Ar is used to heat the container. The furnace is heated continuously at a heating rate of 10 C./min. and kept at 1000 C. for 2 hours. Then, the furnace cools down to room temperature by turning off power, meanwhile keeping Ar flowing. The powder mixture from the container is crushed in a ball mill and screened using sieves. About 2 m of TiC coating forms on the tungsten carbide particles.
Example 2: Hardfacing by PTA
[0050] Two kinds of hardfacings are prepared using PTA. The difference is in tungsten carbide particles only. Conventional tungsten carbide particles and the coated tungsten carbide as disclosed above are used, respectively. In order to observe effect of barrier coating on tungsten carbide, all the other materials and processing parameters are kept the same. Tungsten carbide is spherical cast tungsten with a size of 45 to 150 m. The coating on tungsten carbide particles is TiC with a thickness of about 2 m. A nickel alloy binder is used. Its nominal chemical composition is 0.35-0.45 wt. % C, 1.3-1.9 wt. % Fe, 2.7-4.3 wt. % Si, 1.3-1.9 wt. % B, 8.1-11.0 wt. % Cr, and bal. Ni, and the nominal hardness is HRc 38-43. The binder alloy powders have a size of 45 to 150 m. The hardfacing materials contain 60 wt. % cast tungsten carbide. A piece of 25 mm100 mm12 mm of AISI 4140 steel is used as a substrate. 300 g tungsten carbide particles and 200 g Ni alloy powders are mixed completely. The mixture of tungsten carbide particles and binder alloy powders is loaded into a powder feeder. The used current is 95 A. A carrier gas is Ar and its flowing rate is 3 scfh. A targeting hardfacing thickness is 1.5 mm, which is achieved by one pass. After hardfacing, a cross section metallographic sample is prepared for microstructural observation and microhardness measurement.
[0051]
[0052]
[0053] Advantageously, embodiments of the present disclosure provide the hardfacing composition comprising tungsten carbide particles that have a barrier coating layer. The barrier coating is the metallic carbides, borides, nitrides, or their hybrid compounds, which have high thermodynamic stability. The coatings on the tungsten carbide particles can not only prevent or mitigate the degeneration of the tungsten carbide particles, but also generate a compatible interface with a binder, which would benefit bonding between the coated tungsten carbide particles and the binder in a hardfacing layer. The coated tungsten carbide particles maintain their sizes after welding or brazing, and more importantly, avoid or mitigate detrimental alloying of the binder with tungsten and carbon that result from the dissolution of the tungsten carbide, and the formation of some brittle phases such as eta phase (M.sub.6C), which would cause embrittlement of the binder. Further, the limited dissolution of the coatings on the tungsten carbide particles would add micro-alloying elements such as Ti, Nb, Zr, V, Ta, Hf, or Cr into a binder and thus, improve the properties of the binder. The improved hardfacing materials have a good combination of tough binder, intact tungsten carbide, as well as strong bonding between the tungsten carbide and the binder. All of these features grant the hardfacing layers high qualities and performances including abrasion and erosion wear resistances, and especially impact resistance with higher toughness and a reduced cracking tendency. The improved hardfacing materials will find wide applications in machinery, mining, agriculture, construction, and oil and gas industries, and especially on various earth boring tools such as drill bits, reamers, drill collars, drill pipes, etc.
[0054] While the foregoing written description of the disclosure enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiments, methods, and examples, but by all embodiments and methods within the scope and spirit of the disclosure as claimed.