Multi-metal co-doped wc-co coating and method of making the same

Abstract

This invention provides a multi-metal co-doped WC-Co coating and its preparation method, belonging to the field of metal-ceramic coating technology. The preparation method includes: weighing tungsten, yttrium, cerium, chromium, and vanadium sources, mixing and dissolving them in deionized water, adjusting the pH to 3-4, and obtaining a precursor through co-precipitation, washing, and drying; subjecting the precursor to sequential aerobic calcination, hydrogen reduction, and carbonization treatments to generate a WC phase, resulting in a rare-earth-transition multi-metal co-doped WC-based composite material; using the WC-based composite material, cobalt powder, and additives as raw materials, spraying the raw materials onto the substrate surface via thermal spraying to form a multi-metal co-doped WC-Co coating. The WC-Co coating prepared by this invention incorporates four elements—yttrium, cerium, chromium, and vanadium—forming a multiple synergistic mechanism of grain refinement, interface strengthening, and decarburization inhibition, effectively improving the hardness, wear resistance, corrosion resistance, and toughness of the WC-Co coating.

Description

Technical Field

[0001] This invention belongs to the field of metal-ceramic coating technology, and specifically relates to WC-Co coatings co-doped with multiple metals and their preparation methods. Background Technology

[0002] Tungsten carbide-cobalt (WC-Co) coatings are widely used in wear-resistant and corrosion-resistant components in aerospace, marine engineering, and petrochemical industries due to their high hardness, good wear resistance, and toughness. The core raw material of WC-Co coatings is nano-WC-Co composite powder, composed of tungsten carbide (WC) and cobalt (Co), with tungsten carbide being the main component, directly affecting the performance of the WC-Co coating. To further improve the hardness and other properties of WC-Co coatings, current research involves doping rare earth elements (such as yttrium) into tungsten carbide using mechanical mixing or co-precipitation methods.

[0003] The mechanical mixing method involves physically mixing yttrium oxides or salts with tungsten and carbon sources through ball milling, followed by reduction carbonization to obtain doped WC powder. This method suffers from poor doping uniformity, leading to unstable coating performance, weak interfacial bonding, and severe decarburization during subsequent spraying. The co-precipitation method involves adding yttrium salt solution dropwise during tungsten salt evaporation and crystallization to prepare yttrium-containing tungsten salt (e.g., yttrium-containing ammonium paratungstate) powder, followed by reduction carbonization to obtain yttrium-containing WC powder. While this method is an improvement over mechanical mixing, problems remain, such as yttrium existing as hydroxide precipitates and insufficient doping stability. When applied to WC-Co coatings, its overall performance improvement under complex conditions (e.g., high salt, high humidity, high wear environments) is limited. Furthermore, single yttrium doping has limited ability to inhibit decarburization reactions of WC during thermal spraying, still resulting in the formation of a large amount of brittle W2C phase, thus reducing coating toughness. Summary of the Invention

[0004] In view of this, the present invention provides a multi-metal co-doped WC-Co coating and a method for preparing the same, aiming to solve at least one technical problem in the prior art.

[0005] This invention is implemented as follows: The first aspect of this invention provides a method for preparing a multi-metal co-doped WC-Co coating, the method comprising the following steps: S1. Weigh out tungsten source, yttrium source, cerium source, chromium source and vanadium source in proportion, mix and dissolve in deionized water, adjust the pH of the resulting mixed solution to 3-4, coprecipitate to form a precipitate, wash and dry to obtain the precursor; S2. Under an oxygen atmosphere, the precursor is calcined to remove residual organic matter, resulting in an oxide mixture; S3. Under a hydrogen atmosphere, the oxide mixture is heated to carry out a reduction reaction to obtain a reduction product; S4. A carbon source is added to the reduction product, and a carbonization reaction is carried out by heating to generate a WC phase, thereby obtaining a rare earth-transition multi-metal co-doped WC-based composite material; in the obtained WC-based composite material, yttrium and cerium are co-doped into the WC phase in the form of oxides, and chromium and vanadium are co-doped into the WC phase in the form of carbides. S5. Using the WC-based composite material, cobalt powder, and additives as raw materials, the raw materials are sprayed onto the substrate surface by a thermal spraying method to form a multi-metal co-doped WC-Co coating.

[0006] Furthermore, the tungsten source is ammonium paratungstate; the yttrium source is yttrium nitrate; the cerium source is cerium nitrate; the chromium source is chromium nitrate; and the vanadium source is ammonium metavanadate or vanadium nitrate.

[0007] Furthermore, the calcination temperature in S2 is 500℃~600℃, and the time is 2h~4h; the reduction reaction temperature in S3 is 700℃~800℃, and the time is 2h~4h; the carbonization reaction temperature in S4 is 900℃~1000℃, and the time is 2h~4h.

[0008] Furthermore, based on the mass of tungsten in the tungsten source, the ratio of yttrium to tungsten in the yttrium source is 0.2~0.4:100; the ratio of cerium to tungsten in the cerium source is 0.2~0.4:100; the ratio of chromium to tungsten in the chromium source is 0.4~0.6:100; and the ratio of vanadium to tungsten in the vanadium source is 0.1~0.3:100.

[0009] Furthermore, the carbon source is carbon black or graphite, and the amount of carbon source used is 6wt% to 16wt% of the tungsten element in the reduction product.

[0010] Furthermore, step S5 specifically includes: The WC-based composite material co-doped with multiple metals was mixed with cobalt powder, binder, and dispersant in a certain proportion to obtain a uniform slurry. The slurry is granulated; then the granulated particles are subjected to heat treatment, light crushing and classification in sequence to obtain WC-Co composite powder with a particle size distribution of 15μm~45μm. The WC-Co composite powder is sprayed onto the substrate surface using a thermal spraying method to form a multi-metal co-doped WC-Co coating.

[0011] Furthermore, the amount of cobalt powder used is 8wt% to 12wt% of the WC-based composite material.

[0012] Furthermore, the dispersant is ammonium polyacrylate, and its dosage is 0.2wt% to 0.8wt% of the WC-based composite material. The binder is polyvinyl alcohol, polyethylene glycol or methylcellulose, and its amount is 1wt% to 3wt% of the WC-based composite material.

[0013] Furthermore, the heat treatment is carried out under a protective atmosphere at a temperature of 600℃~800℃ for a time of 0.5h~2h.

[0014] The second aspect of the present invention provides a multi-metal co-doped WC-Co coating prepared by the above-described method.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses rare earth-transition metal co-doped WC-based composite materials to prepare WC-Co coatings. The coating is doped with four elements, yttrium, cerium, chromium and vanadium, to form a multi-synergistic mechanism of grain refinement, interface strengthening and decarburization inhibition, which effectively improves the hardness, wear resistance, corrosion resistance and toughness of the WC-Co coating.

[0016] 2. This invention employs a co-precipitation method to prepare rare-earth-transition multi-metal co-doped WC-based composite materials; Y 3+ Ce 3 + Cr 3+ V 3+ (VO) 2+ First, through coordination reactions, the elements are atomically and uniformly anchored to the surface of amorphous scheelite in the form of WOM chemical bonds, forming stable WOY, WO-Ce, WO-Cr, and WOV chemical bonds respectively, so that the four elements are uniformly anchored on the particle surface in an atomically dispersed state. Subsequently, combined with multi-stage heat treatment, yttrium and cerium are co-doped into the WC phase in the form of oxides, and chromium and vanadium are co-doped into the WC phase in the form of carbides. This avoids the segregation problem caused by physical mixing in the prior art, resulting in a uniform coating structure and stable performance.

[0017] 3. The four elements doped in this invention achieve a synergistic effect. Y (yttrium) is used to refine WC grains, promote the formation of a dense Y2O3 passivation film, and improve corrosion resistance. Ce (cerium) is used to further refine grains, improve the density of the oxide layer, and significantly enhance the resistance to high-temperature oxidation. Cr (chromium) reacts with C to generate Cr3C2 and other carbides, which enhance the WC / Co interface bonding, inhibit decarburization, and improve corrosion resistance. V (vanadium) reacts with C to generate VC and other carbides, which refine grains and significantly improve hardness and wear resistance, resulting in a synergistic effect of "1+1+1+1>4".

[0018] 4. The present invention has excellent decarburization inhibition effect. The Y, Ce, Cr and V uniformly distributed in the coating form a multi-element enrichment layer on the WC surface, which effectively inhibits the diffusion of W and C, reduces the formation of brittle W2C phase, and significantly improves the toughness of the coating. Attached Figure Description

[0019] Figure 1 Here is a SEM image of the WC-based composite material prepared in Example 1 of this invention; Figure 2 The images show the TEM and EDS spectra of the WC-based composite material prepared in Example 1 of this invention. Figure 3 This is a SEM image of the WC-Co coating obtained in Example 1 of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] A method for preparing a multi-metal co-doped WC-Co coating includes the following steps: S1. Weigh out tungsten source, yttrium source, cerium source, chromium source and vanadium source in proportion, mix and dissolve in deionized water, adjust the pH of the resulting mixed solution to medium acidity (3~4), coprecipitate to form a precipitate, wash and dry to obtain the precursor; The tungsten source is ammonium paratungstate; the yttrium source is yttrium nitrate; the cerium source is cerium nitrate; the chromium source is chromium nitrate; and the vanadium source is ammonium metavanadate or vanadium nitrate.

[0022] Based on the mass of tungsten in the tungsten source, the ratio of yttrium to tungsten in the yttrium source is 0.2~0.4:100; the ratio of cerium to tungsten in the cerium source is 0.2~0.4:100; the ratio of chromium to tungsten in the chromium source is 0.4~0.6:100; and the ratio of vanadium to tungsten in the vanadium source is 0.1~0.3:100.

[0023] In the coprecipitation reaction, the system generates amorphous scheelite nanoparticles rich in W-OH bonds. Under these conditions, the particles have small size, large specific surface area, and abundant surface active sites, providing an ideal carrier for multi-element coordination and anchoring. 3+ Ce 3+ Cr 3+ V 3+ (or VO) 2+ In solution, the W-OH groups on the particle surface undergo coordination reactions, forming stable WOY, WO-Ce, WO-Cr, and WOV chemical bonds, respectively, thus uniformly anchoring the four elements to the particle surface in an atomically dispersed state. Unlike existing technologies where dopants exist as hydroxide precipitates, this invention achieves multi-metal co-doping through chemical bonding, significantly improving the uniformity and stability of doping. In this precursor, Y, Ce, Cr, V, and W are uniformly mixed at the molecular / atomic scale; avoiding the segregation problems caused by physical mixing in existing technologies, resulting in a uniform coating structure and stable performance.

[0024] S2. Under an oxygen-rich atmosphere, the precursor is calcined at 500℃~600℃ for 2h~4h to remove residual organic matter, yielding an oxide mixture; some Y and Ce exist in the form of Y2O3 and CeO2.

[0025] S3. Under a hydrogen atmosphere, the oxide mixture is reduced at 700℃~800℃ for 2h~4h to obtain a reduction product; the oxide is reduced to a mixture of metals W, Y, Ce, Cr and V.

[0026] S4. A carbon source (carbon black or graphite, with a carbon to tungsten mass ratio of 6~16:100, i.e., the amount of carbon source is 6wt%~16wt% of the tungsten in the reduction product) is added to the reduction product, and carbonized at 900℃~1000℃ for 2h~4h to generate the WC phase, thereby obtaining a rare earth-transition multi-metal co-doped WC-based composite material.

[0027] In the obtained WC-based composite material, yttrium and cerium are co-doped into the WC phase in the form of oxides (Y2O3 and CeO2 or Ce2O3); chromium and vanadium are co-doped into the WC phase in the form of carbides (Cr3C2 and VC).

[0028] Yttrium (Y) and cerium (Ce) are uniformly distributed in the WC matrix as Y₂O₃ and CeO₂ or Ce₂O₃, refining the grains and pinning grain boundaries. Y refines the WC grains, promoting the formation of a dense Y₂O₃ passivation film and improving corrosion resistance. Ce further refines the grains, improves the density of the oxide layer, and significantly enhances resistance to high-temperature oxidation. Cr reacts with C to form carbides Cr₃C₂, strengthening the WC / Co interface and inhibiting decarburization. V reacts with C to form carbides VC, further refining the grains and improving hardness and wear resistance. The synergistic effect of these four elements effectively inhibits WC grain coarsening while reducing the formation of brittle W₂C phases. The four elements form a multiple synergistic mechanism of grain refinement, interface strengthening, and decarburization inhibition, producing a synergistic effect greater than 4 (1+1+1+1>4). The uniformly distributed Y, Ce, Cr, and V form a multi-element enrichment layer on the WC surface, which effectively inhibits the diffusion of W and C, reduces the formation of brittle W2C phase, and significantly improves the toughness of the coating.

[0029] S5. Using the WC-based composite material, cobalt powder, and additives as raw materials, the raw materials are sprayed onto the substrate surface by a thermal spraying method to form a multi-metal co-doped WC-Co coating.

[0030] Specifically, it includes: (1) The above-mentioned multi-metal co-doped WC-based composite material is mixed with cobalt powder, binder, and dispersant in a certain proportion to obtain a uniform slurry; the amount of cobalt powder is 8% to 12% of the mass of the WC-based composite material; the dispersant is ammonium polyacrylate, and its amount range is 0.2wt% to 0.8wt% (based on the mass of the WC-based composite material); the binder is polyvinyl alcohol, polyethylene glycol, or methylcellulose, and its amount range is 1wt% to 3wt%. (2) Granulate the slurry; such as by spray drying to form spherical or near-spherical particles with good flowability and loose density to meet the requirements of subsequent thermal spraying for powder feeding; (3) The granulated particles are subjected to heat treatment in sequence; specifically: the heat treatment is carried out under a protective atmosphere at a temperature of 600℃~800℃ for 0.5h~2h. The heat treatment causes the binder to decompose and slight sintering to occur inside the particles, thereby improving the particle strength and preventing the particles from breaking during the spraying process; (4) The heat-treated particles are lightly crushed and obtained by sieving or air classification to obtain WC-Co composite powder with a particle size distribution of 15μm~45μm, which meets the requirements of subsequent thermal spraying for powder particle size. (5) The WC-Co composite powder is sprayed onto the cleaned substrate surface by a thermal spraying method (such as HVOF method) to form a multi-metal co-doped WC-Co coating.

[0031] Example 1 A method for preparing a multi-metal co-doped WC-Co coating includes the following steps: S1. Take 100g of ammonium paratungstate, and weigh out yttrium nitrate, cerium nitrate, chromium nitrate, and ammonium metavanadate according to the following mass ratios: Y / W 0.3:100, Ce / W 0.3:100, Cr / W 0.5:100, and V / W 0.2:100, respectively. Dissolve them in deionized water. Slowly add concentrated nitric acid while stirring to adjust the pH of the system to 3.5. The reaction produces an amorphous scheelitic acid precipitate. 3+ Ce 3+ Cr 3+ VO 2+ The precursor powder was obtained by anchoring the precursor to the precipitate surface through coordination reaction, followed by co-precipitation, filtration, washing, and drying at 80°C for 12 hours.

[0032] S2. The precursor was calcined in air at 550°C for 2 hours to obtain an oxide mixture.

[0033] S3. The oxide mixture is reduced at 750°C for 2 hours under a hydrogen atmosphere to obtain the reduction product.

[0034] S4. Carbon black (at a mass ratio of carbon black to tungsten of 10:100) was added to the reduction product, and the mixture was carbonized at 950℃ for 3 hours to generate the WC phase, yielding a rare earth-transition multi-metal (Y-Ce-Cr-V) co-doped WC-based composite material. Its SEM image is shown below. Figure 1 As shown, the average grain size D50 of the WC-based composite material is approximately 0.22 μm, and its TEM and EDS are as follows. Figure 2 As shown, this indicates that all elements are uniformly doped in the WC-based composite material.

[0035] S5. Add 10wt% cobalt powder, 2wt% polyvinyl alcohol binder, and 0.5wt% ammonium polyacrylate dispersant (based on the mass of the WC-based composite material) to the above WC-based composite material and mix to form a slurry. Spray dry to obtain spherical particles, heat treat at 650℃ under an argon atmosphere for 1 hour, and then perform light crushing and air classification to obtain WC-Co composite powder with a particle size range of 15μm~45μm. Use the HVOF method to spray the WC-Co composite powder onto a pretreated (sandblasted, cleaned) 316L stainless steel substrate to form a multi-metal co-doped WC-Co coating with a thickness of approximately 200μm. The SEM image is shown below. Figure 3 As shown.

[0036] Example 2 A method for preparing a multi-metal co-doped WC-Co coating includes the following steps: S1. Take 100g of ammonium paratungstate, and weigh out yttrium nitrate, cerium nitrate, chromium nitrate, and vanadium nitrate according to the following mass ratios: Y / W 0.3:100, Ce / W 0.3:100, Cr / W 0.5:100, and V / W 0.2:100, respectively. Dissolve them in deionized water. Slowly add concentrated nitric acid while stirring to adjust the pH of the system to 3.5. The reaction produces an amorphous scheelitic acid precipitate. 3+ Ce 3+ Cr 3+ VO 2+ The precursor powder was obtained by anchoring the precursor to the precipitate surface through coordination reaction, followed by co-precipitation, filtration, washing, and drying at 80°C for 12 hours.

[0037] S2. The precursor powder was calcined in air at 500°C for 3 hours to obtain an oxide mixture.

[0038] S3. The oxide mixture is reduced at 700°C for 3 hours under a hydrogen atmosphere to obtain the reduction product.

[0039] S4. Graphite (with a mass ratio of graphite to tungsten of 10:100) is added to the reduction product and carbonized at 900℃ for 3 hours to generate the WC phase, thus obtaining a rare earth-transition multi-metal (Y-Ce-Cr-V) co-doped WC-based composite material.

[0040] S5. Add 10wt% cobalt powder, 2wt% polyvinyl alcohol binder, and 0.5wt% ammonium polyacrylate dispersant (based on the mass of the WC-based composite material) to the above WC-based composite material and mix to form a slurry. Spray dry to obtain spherical particles, heat treat at 600℃ under an argon atmosphere for 1 hour, and then lightly crush and air classify to obtain WC-Co composite powder with a particle size range of 15μm~45μm. Use the HVOF method to spray the WC-Co composite powder onto a pretreated (sandblasted, cleaned) 316L stainless steel substrate to form a multi-metal co-doped WC-Co coating with a thickness of approximately 200μm.

[0041] Example 3 A method for preparing a multi-metal co-doped WC-Co coating includes the following steps: S1. Take 100g of ammonium paratungstate, and weigh out yttrium nitrate, cerium nitrate, chromium nitrate, and ammonium metavanadate according to the following mass ratios: Y / W 0.3:100, Ce / W 0.3:100, Cr / W 0.5:100, and V / W 0.2:100, respectively. Dissolve them in deionized water. Slowly add concentrated nitric acid while stirring to adjust the pH of the system to 3.5. The reaction produces an amorphous scheelitic acid precipitate. 3+ Ce 3+ Cr 3+ VO 2+ The precursor powder was obtained by anchoring the precursor to the precipitate surface through coordination reaction, followed by co-precipitation, filtration, washing, and drying at 80°C for 12 hours.

[0042] S2. The precursor powder was calcined in air at 600°C for 2 hours to obtain an oxide mixture.

[0043] S3. The oxide mixture is reduced at 800°C for 2 hours under a hydrogen atmosphere to obtain the reduction product.

[0044] S4. Graphite (with a mass ratio of graphite to tungsten of 10:100) is added to the reduction product and carbonized at 1000℃ for 2 hours to generate the WC phase, thus obtaining a rare earth-transition multi-metal (Y-Ce-Cr-V) co-doped WC-based composite material.

[0045] S5. Add 10wt% cobalt powder, 2wt% polyvinyl alcohol binder, and 0.5wt% ammonium polyacrylate dispersant (based on the mass of the WC-based composite material) to the above WC-based composite material and mix to form a slurry. Spray dry to obtain spherical particles, heat treat at 800℃ under an argon atmosphere for 1 hour, and then lightly crush and air classify to obtain WC-Co composite powder with a particle size range of 15μm~45μm. Use the HVOF method to spray the WC-Co composite powder onto a pretreated (sandblasted, cleaned) 316L stainless steel substrate to form a multi-metal co-doped WC-Co coating with a thickness of approximately 200μm.

[0046] Example 4 The difference between this embodiment and Embodiment 1 is that the pH of the system is adjusted to 3 in step S1, while the other conditions and steps are the same as in Embodiment 1.

[0047] Example 5 The difference between this embodiment and Embodiment 1 is that the pH of the system is adjusted to 4 in step S1, while the other conditions and steps are the same as in Embodiment 1.

[0048] Comparative Example 1 The difference between this comparative example and Example 1 is that only ammonium paratungstate is used as the raw material in S1, while other conditions and steps are the same as in Example 1. Therefore, the final product is a WC-Co coating without elemental doping.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that cerium nitrate, chromium nitrate, and ammonium metavanadate are removed from the raw materials in S1. Other conditions and steps are the same as in Example 1. The final product is a WC-Co coating doped with Y as a single element.

[0050] Comparative Example 3 The difference between this comparative example and Example 1 is that cerium nitrate and ammonium metavanadate are removed from the raw materials in S1. Other conditions and steps are the same as in Example 1. The final product is a WC-Co coating doped with Y-Cr.

[0051] Comparative Example 4 The difference between this comparative example and Example 1 is that yttrium nitrate is removed from the raw materials in S1, while other conditions and steps are the same as in Example 1. The final product is a Ce-Cr-V three-element doped WC-Co coating.

[0052] Comparative Example 5 The difference between this comparative example and Example 1 is that cerium nitrate is removed from the raw materials in S1, while other conditions and steps are the same as in Example 1. The final product is a WC-Co coating doped with Y-Cr-V elements.

[0053] Comparative Example 6 The difference between this comparative example and Example 1 is that chromium nitrate is removed from the raw materials in S1, while other conditions and steps are the same as in Example 1. The final product is a WC-Co coating doped with Y-Ce-V elements.

[0054] Comparative Example 7 The difference between this comparative example and Example 1 is that ammonium metavanadate is removed from the raw materials in S1, while other conditions and steps are the same as in Example 1. The final product is a WC-Co coating doped with Y-Ce-Cr tri-element.

[0055] Comparative Example 8 The difference between this comparative example and Example 1 is that the calcination treatment in step S2 is omitted, and the precursor is directly reduced in step S3. Other conditions and steps are the same as in Example 1.

[0056] Comparative Example 9 The difference between this comparative example and Example 1 is that the reduction treatment in step S3 is omitted, and the product obtained in S2 is directly carbonized in step S4. Other conditions and steps are the same as in Example 1.

[0057] Comparative Example 10 The difference between this comparative example and Example 1 is that the pH of the system in S1 is adjusted to 2.5, while the other conditions and steps are the same as in Example 1.

[0058] Comparative Example 11 The difference between this comparative example and Example 1 is that the pH of the system in S1 is adjusted to 4.5, while the other conditions and steps are the same as in Example 1.

[0059] Comparative Example 12 The difference between this comparative example and Example 1 is that the compounds corresponding to the Y-Ce-Cr-V elements are directly added to the WC powder and Co powder, instead of using the co-precipitation method with WC.

[0060] The specific steps of this comparative example are as follows: Yttrium oxide, cerium oxide, chromium carbide, and vanadium carbide (after mixing, D50 = 50 nm) were weighed according to the Y / W mass ratio of 0.3:100, Ce / W mass ratio of 0.3:100, Cr / W mass ratio of 0.5:100, and V / W mass ratio of 0.2:100, respectively. They were added to the WC hard phase (D50 = 0.25 μm) and ball-milled for 120 h. Then, 10 wt% cobalt powder, 2 wt% polyvinyl alcohol binder, and 0.5 wt% ammonium polyacrylate dispersant (based on the mass of the WC hard phase) were added, mixed and slurried, spray-dried to obtain spherical particles, heat-treated at 650℃ under an argon atmosphere for 1 h, and obtained WC-Co composite powder with a particle size range of 15 μm to 45 μm after light crushing and air classification. WC-Co composite powder was sprayed onto a pretreated (sandblasted, cleaned) 316L stainless steel substrate using the HVOF method to form a WC-Co coating.

[0061] The performance of the WC-Co coatings prepared in Examples 1 to 5 and Comparative Examples 1 to 12 was tested, with three parallel samples for each example and the average value was taken. In addition, the average grain size D50 of the WC-based composite material prepared in step S4 was tested. The results are shown in Table 1.

[0062] The standard / method for testing the coating hardness is to use a Vickers hardness tester with a load of 300g and a holding time of 15s. At least 10 indentation points are randomly selected for each sample. The measurement accuracy of the diagonal length of the indentation is 0.1μm, and the indentation depth should be less than 1 / 10 of the coating thickness (the coating thickness is about 200μm, and the indentation depth is <20μm) to eliminate the influence of the substrate.

[0063] The testing standard / method for coating wear rate was to use a reciprocating friction and wear testing machine with Si3N4 grinding balls (6mm in diameter). Test parameters: normal load 10N, reciprocating frequency 200r / min, single reciprocating stroke 5mm, test time 30min, total sliding distance 60m. After the test, the wear volume V (mm²) of the coating surface was measured using a three-dimensional profilometer. 3 The wear rate is W = V / (F·S), where F is the normal load (10N) and S is the total sliding distance (60m).

[0064] The standard / method for testing coating corrosion current density is a three-electrode system, with the working electrode being the coating sample (exposed area 1 cm²). 2 The reference electrode was a saturated calomel electrode (SCE), and the auxiliary electrode was a platinum sheet. The corrosive medium was a 3.5 wt% NaCl solution (25℃). The open-circuit potential was first stabilized for 30 min, and then the polarization curve was recorded by scanning from -0.3 V to +0.5 V relative to the open-circuit potential at a scan rate of 0.5 mV / s. The self-corrosion current density i was obtained by fitting using the Tafel extrapolation method. corr .

[0065] The testing standard / method for coating toughness is as follows: using a Vickers hardness tester, a load of 5 kgf (49.03 N), and holding the load for 15 seconds. The half-length of the indentation diagonal, *a*, and the half-length of the total crack length, *c* (from the indentation center to the crack tip), are measured. An indentation with a length of 0.6 ≤ *c* / *a* ≤ 4.5 is selected. Fracture toughness K... IC Calculate according to the Niihara or Wilshaw formula. Measure at least 10 valid indentations for each sample and take the average value.

[0066] Table 1

[0067] Table 1 shows that the hardness, wear resistance, corrosion resistance, and toughness of the WC-Co coating co-doped with quaternary metal elements are all improved to varying degrees compared with the undoped, single yttrium, binary metal element, and ternary metal doped (Comparative Examples 1 to 7) coatings. The formation of VC and Cr3C2 and the grain refinement effect of Y and Ce contribute to the increase in hardness; high hardness and strong interfacial bonding enhance wear resistance; Y and Ce promote the formation of a dense passivation film, and Cr and V enhance interfacial stability. The four elements synergistically improve corrosion resistance.

[0068] The difference between Examples 1 and 3 lies in adjusting the temperature conditions of steps S2-S5. The results show that as the calcination, reduction, and carbonization temperatures increase, the WC grain size slightly increases, the coating hardness gradually decreases, the wear rate gradually increases, the corrosion current density gradually increases, and the fracture toughness gradually decreases. The results indicate that within the preferred temperature range (S2 calcination 500℃~550℃, S3 reduction 700℃~750℃, S4 carbonization 900℃~950℃), finer grains and better overall performance can be obtained; excessively high temperatures promote grain coarsening, reducing hardness, wear resistance, corrosion resistance, and toughness.

[0069] The results of Examples 1, 3, and 4, and Comparative Examples 10 and 11 show that when pH = 3-4, the system generates amorphous scheelite nanoparticles rich in W-OH bonds. 3+ Ce 3+ Cr 3+ VO 2+ Stable WOM chemical bonds are formed through coordination reactions, achieving atomically uniform doping. The resulting coating exhibits finer grains and superior overall performance (high hardness, strong wear resistance, excellent corrosion resistance, and high fracture toughness). When the acidity is too strong, pH < 3 (e.g., Comparative Example 10, pH = 2.5), the H in the system... + Excessive concentration inhibited the formation of W–OH bonds, and Y 3+ Ce 3+ The inability to form coordination anchors leads to decreased doping uniformity, reduced coating hardness and toughness, and increased wear rate and corrosion current density. This is because, under excessively acidic conditions, the amorphous scheelite structure is destroyed, resulting in uneven distribution of dopant elements. Subsequent reduction and carbonization leads to WC grain growth and an increase in brittle phases. When the acidity is too weak, with pH > 4 (e.g., Comparative Example 11, pH = 4.5), the OH groups in the system... - As concentration increases, Y 3+ Ce 3+ Preferred to be OH - The reaction produces Y(OH)3 and Ce(OH)3 precipitates, which are difficult to coordinate with W–OH, resulting in the dopant elements existing in a physically mixed form, leading to poor uniformity; the coating hardness and toughness decrease, the wear rate and corrosion current density increase, and the grain size coarsens; the reason is that under weakly acidic conditions, the coordination anchoring mechanism is suppressed, and the dopant elements fail to effectively embed into the WC precursor, ultimately leading to a decline in performance.

[0070] A comparison of Examples 1, 8, and 9 shows that when either the calcination or reduction process is omitted, the coating performance deteriorates significantly. The reason for this is: In Comparative Example 8 (calcination treatment removed), the precursor was directly subjected to hydrogen reduction and carbonization. The precursor contained a large number of residual organic functional groups and water of crystallization, which rapidly decomposed during reduction to generate gas, causing internal porosity and cracks in the particles. Simultaneously, Y and Ce failed to be pre-converted into Y₂O₃ and CeO₂, resulting in uneven distribution of dopant elements during subsequent carbonization. The coating hardness and toughness decreased significantly, while the wear rate and corrosion current density increased significantly, and the grains became noticeably coarser. This indicates that the calcination step is crucial for removing organic matter, pre-oxidizing dopant elements, and forming a homogeneous oxide mixture.

[0071] In Comparative Example 9 (reduction treatment removed), the calcined oxide mixture was directly added to a carbon source for carbonization. Since it was not reduced with hydrogen, W existed as WO3, and the carbonization reaction required simultaneous reduction of W. 6+ The carbonization process is complex, resulting in incomplete carbonization and the presence of large amounts of W, W₂C, and oxide phases in the product, leading to a loose structure. The coating exhibits significantly reduced hardness and toughness, a significantly increased wear rate and corrosion current density, and marked grain coarsening. This indicates that the hydrogen reduction step can pre-reduce tungsten oxide to metallic W, significantly reducing the difficulty of subsequent carbonization and ensuring the purity and density of the WC phase.

[0072] In Comparative Example 12, the compounds corresponding to Y-Ce-Cr-V were added to WC material through mechanical mixing. The results showed that the hardness and fracture toughness of the WC-Co coating prepared by this method decreased significantly, while the wear rate and corrosion current density increased significantly. In addition, the average grain size of the raw materials (such as the WC hard phase, yttrium oxide + cerium oxide + chromium carbide + vanadium carbide mixture) was at the micrometer / nanometer level. Therefore, the size after ball milling was not much different from that of Example 1, but the overall performance of the coating was significantly worse than that of Example 1. The reason is that: (1) the dopant elements did not achieve atomic-level uniform distribution: the mechanical mixing method cannot achieve the uniform distribution of dopant elements at the atomic scale. The compounds of Y, Ce, Cr and V exist in the interstices or surface of WC particles in the form of micrometer-level agglomerates. The local segregation is serious and cannot form atomic-level WOM chemical bonds. (2) Lack of in-situ reaction-enhanced interfacial bonding: The wet chemical coprecipitation method of this invention anchors Y, Ce, Cr, and V atoms to the surface of WC precursor through WOM coordination bonds. In subsequent heat treatment, they are transformed in situ into reinforcing phases such as Y2O3, CeO2, Cr3C2, and VC, which form coherent or semi-coherent interfaces with WC and have high bonding strength. In contrast, in mechanical mixing, the added Y2O3, Cr3C2 particles only have physical contact with WC and are easily detached during spraying, failing to play an effective role in grain pinning and interfacial strengthening. (3) Insufficient decarburization inhibition: The Cr and V compounds in mechanical mixing cannot uniformly coat the WC surface and cannot form a dense multi-element enriched layer. Decarburization will still occur during subsequent heat treatment, generating more brittle W2C phases, thereby reducing the coating performance.

[0073] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a multi-metal co-doped WC-Co coating, characterized in that, The preparation method includes the following steps: S1. Weigh out tungsten source, yttrium source, cerium source, chromium source and vanadium source in proportion, mix and dissolve in deionized water, adjust the pH of the resulting mixed solution to 3-4, coprecipitate to form a precipitate, wash and dry to obtain the precursor; S2. Under an oxygen atmosphere, the precursor is calcined to remove residual organic matter, resulting in an oxide mixture; S3. Under a hydrogen atmosphere, the oxide mixture is heated to carry out a reduction reaction to obtain a reduction product; S4. A carbon source is added to the reduction product, and a carbonization reaction is carried out by heating to generate a WC phase, thereby obtaining a rare earth-transition multi-metal co-doped WC-based composite material; in the obtained WC-based composite material, yttrium and cerium are co-doped into the WC phase in the form of oxides, and chromium and vanadium are co-doped into the WC phase in the form of carbides. S5. Using the WC-based composite material, cobalt powder, and additives as raw materials, the raw materials are sprayed onto the substrate surface by a thermal spraying method to form a multi-metal co-doped WC-Co coating.

2. The method for preparing a multi-metal co-doped WC-Co coating according to claim 1, characterized in that, The tungsten source is ammonium paratungstate; the yttrium source is yttrium nitrate; the cerium source is cerium nitrate; the chromium source is chromium nitrate; and the vanadium source is ammonium metavanadate or vanadium nitrate.

3. The method for preparing a multi-metal co-doped WC-Co coating according to claim 2, characterized in that, The calcination temperature in S2 is 500℃~600℃, and the time is 2h~4h; the reduction reaction temperature in S3 is 700℃~800℃, and the time is 2h~4h; the carbonization reaction temperature in S4 is 900℃~1000℃, and the time is 2h~4h.

4. The method for preparing a multi-metal co-doped WC-Co coating according to claim 1, characterized in that, Based on the mass of tungsten in the tungsten source, the ratio of yttrium to tungsten in the yttrium source is 0.2~0.4:100; the ratio of cerium to tungsten in the cerium source is 0.2~0.4:100; the ratio of chromium to tungsten in the chromium source is 0.4~0.6:100; and the ratio of vanadium to tungsten in the vanadium source is 0.1~0.3:

100.

5. The method for preparing a multi-metal co-doped WC-Co coating according to claim 1, characterized in that, The carbon source is carbon black or graphite, and the amount of carbon source used is 6wt% to 16wt% of the tungsten element in the reduction product.

6. The method for preparing a multi-metal co-doped WC-Co coating according to claim 1, characterized in that, Step S5 specifically includes: The WC-based composite material co-doped with multiple metals was mixed with cobalt powder, binder, and dispersant in a certain proportion to obtain a uniform slurry. The slurry is granulated; then the granulated particles are subjected to heat treatment, light crushing and classification in sequence to obtain WC-Co composite powder with a particle size distribution of 15μm~45μm. The WC-Co composite powder is sprayed onto the substrate surface using a thermal spraying method to form a multi-metal co-doped WC-Co coating.

7. The method for preparing a multi-metal co-doped WC-Co coating according to claim 6, characterized in that, The amount of cobalt powder used is 8wt% to 12wt% of the WC-based composite material.

8. The method for preparing a multi-metal co-doped WC-Co coating according to claim 6, characterized in that, The dispersant is ammonium polyacrylate, and its dosage is 0.2wt% to 0.8wt% of the WC-based composite material. The binder is polyvinyl alcohol, polyethylene glycol or methylcellulose, and its amount is 1wt% to 3wt% of the WC-based composite material.

9. The method for preparing a multi-metal co-doped WC-Co coating according to claim 6, characterized in that, The heat treatment is carried out under a protective atmosphere at a temperature of 600℃~800℃ for a time of 0.5h~2h.

10. The WC-Co coating prepared by the method of any one of claims 1 to 9 is a multi-metal co-doped WC-Co coating.

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