Preparation Method and Application of a Rare Earth La2O3 / CeO2 Co-Doped WC-Co Thermal Spraying Powder

Abstract

The present invention relates to a preparation method and application of rare earth La₂O₃ / CeO₂ co-doped WC-Co thermal spraying powder. The preparation method includes: (1) mixing lanthanum salt, cerium salt, cobalt salt and tungsten salt with a solvent to obtain a mixed slurry; (2) adding a complexing agent and a crosslinking agent to the mixed slurry, stirring and mixing, and then performing a gelation treatment to obtain a gel material; subsequently, performing a supercritical drying treatment to obtain a precursor material; (3) performing a plasma reduction treatment and a post-treatment on the precursor material to obtain the thermal spraying powder. The preparation method of the present invention realizes the atomic-level dispersion of rare earth and the directional doping of WC lattice, breaks through the physical limit of traditional mechanical mixing, and improves key technical indexes such as the corrosion resistance of the coating and the upper limit of the service temperature.

Description

Technical Field

[0001] The present invention relates to the technical fields of spraying materials and coating preparation, and particularly relates to a preparation method and application of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. Background Art

[0002] WC-Co powder is a metal wear-resistant coating material made of tungsten carbide particles and cobalt-based alloys as raw materials. WC-Co coatings are often prepared by thermal spraying methods. This coating has extremely high hardness and good wear resistance, and is one of the most widely used materials in metal wear-resistant coatings. The structure of WC-Co hard alloy coatings depends on the composition, structure, spraying process method and specific process parameters of the initial powder, and is usually applicable to abrasive wear and erosion wear working conditions below 540 °C, such as the metallurgy, mining, petroleum and other industries.

[0003] CN103266311A discloses a preparation method of WC-Co powder doped with rare earth elements. The preparation method is to prepare rare earth oxides in a plating solution as the addition method of rare earth. When hydrazine is used in the plating solution to reduce Co salts to Co and coat it on the surface of WC powder, rare earth metal oxides are embedded in the Co coating at the same time. This method is suitable for trace rare earth addition, but the process is cumbersome, time-consuming, and requires pre-ball milling of WC powder and Co salt powder in a ball milling tank respectively, which is time-consuming and the controllability of subsequent reaction steps is poor.

[0004] CN111590081A discloses a preparation method of WC-Co powder for spraying, which combines traditional high-energy ball milling and vacuum sintering processes to add rare earth elements, and is a mechanical mixing for physical coating. Rare earth elements are attached to the surface of WC in the form of nanoparticles, and the dispersion degree is low. Moreover, since the WC-rare earth binding method is physical adsorption or grain boundary segregation, its interfacial energy is high and it is easy to peel off. There are disadvantages such as large grain size and high energy consumption in the preparation process.

[0005] CN112591753A discloses a preparation method of rare earth-doped tungsten carbide composite powder. Water-soluble rare earth salts, water-soluble tungsten salts, water-soluble organic carbon sources and water are mixed, and the obtained mixed material liquid is directly prepared into rare earth-doped tungsten carbide composite powder by spray drying and two-step calcination, without first preparing tungsten carbide powder and then ball milling with rare earth oxides. Moreover, rare earth oxides are molecularly dispersed in the grain boundaries of tungsten carbide, making the composition of the composite powder reach an almost ideal uniform state, which can effectively inhibit cracks in the coating and improve the structure and performance of the coating. However, it still has disadvantages such as large grain size and high energy consumption in the preparation process.

[0006] In the above prior arts, the WC-Co thermal spraying coatings prepared from traditional powders have the following problems:

[0007] 1. High-temperature oxidation and corrosion failure: WC rapidly oxidizes to form WO3 above 600 °C (volume expansion causes coating cracking), and the Co binder phase is prone to corrosion in acidic / salt spray environments (corrosion rate > 0.5 mm / a);

[0008] 2. Limitations of single rare-earth doping: Existing technologies mostly use single rare earths (such as La2O3 or Y2O3) for modification, which cannot balance the requirements of high-temperature oxidation resistance and corrosion resistance. Moreover, uneven dispersion of nano-rare earths leads to fluctuations in coating properties, such as large deviations in hardness;

[0009] 3. Defects in powder preparation process: The mechanical mixing method is difficult to achieve atomic-level combination of rare earths and WC-Co. During the spraying process, rare earths are prone to volatilization with a high loss rate, reducing the modification effect.

[0010] To address the above problems, it is urgent to develop a WC-Co composite powder co-doped with La2O3 / CeO2, achieve uniform distribution of rare earths through process innovation, and design a supporting coating structure to adapt to the multi-factor coupling working conditions of medium and high-temperature corrosion. Summary of the Invention

[0011] To solve the above technical problems, the present invention provides a preparation method and application of a rare-earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The preparation method of the present invention realizes atomic-level dispersion of rare earths and directional doping of WC lattice through two-step processes of precursor chemical synthesis and plasma reduction treatment, breaking through the physical limit of traditional mechanical mixing, thereby improving key technical indicators such as coating corrosion resistance and upper limit of service temperature.

[0012] To achieve this purpose, the present invention adopts the following technical solutions:

[0013] In the first aspect, the present invention provides a preparation method of a rare-earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder, and the preparation method includes:

[0014] (1) Mix lanthanum salt, cerium salt, cobalt salt, and tungsten salt with a solvent to obtain a mixed slurry;

[0015] (2) Add a complexing agent and a cross-linking agent to the mixed slurry, stir and mix, then perform gelation treatment to obtain a gel material; subsequently, perform supercritical drying treatment to obtain a precursor material;

[0016] (3) Perform plasma reduction treatment and post-treatment on the precursor material to obtain the thermal spraying powder.

[0017] The present invention prepares a precursor by chelating a complexing agent and a crosslinking agent, achieving a molecular-level uniform mixing of lanthanum, cerium, cobalt, and tungsten elements. Combining with the plasma instantaneous high-temperature reduction process, rare-earth atoms replace the W sites in the WC lattice, greatly improving the rare-earth doping efficiency.

[0018] Since the Gibbs free energy (ΔGf) of La2O3 is significantly lower than that of the WC oxidation product (WO3) at high temperatures, it preferentially reacts to form a protective layer (such as La2(WO4)3), and the La 3+ ionic radius (1.06 Å) is significantly different from that of W 4+ (0.68 Å), which can hinder the diffusion of W atoms, thus inhibiting the oxidation reaction kinetics. Therefore, the preparation method of the present invention enables La2O3 to react with the WC surface at high temperatures (>600 °C), inhibiting the high-temperature oxidation of WC, thereby forming stable compounds such as La2(WO4)3 and LaCrO3, covering the surface of WC particles, blocking the oxygen diffusion path, and significantly reducing the oxidation rate. Therefore, in the present invention, the doping of lanthanum and cerium elements utilizes the thermodynamic stability and kinetic inhibition effects to inhibit the formation of WC oxidation products, thereby improving the high-temperature oxidation resistance of the coating.

[0019] In the present invention, La2O3 nanoparticles are used as heterogeneous nucleating agents to inhibit the abnormal growth of WC grains during sintering or spraying, refining the grain size (from 1 - 2 μm to 0.3 - 0.5 μm), thereby improving the hardness of the material.

[0020] Since the interfacial binding energy (≥2 J / m²) between La2O3 and the Co-based binder phase is higher than that of the pure WC-Co interface (1.5 J / m²), it can significantly reduce the risk of interfacial peeling. The addition of La2O3 reduces the internal stress in the coating (the thermal expansion coefficients are more matched), and at the same time inhibits crack propagation through the pinning effect (the fracture toughness increases from 8 MPa·m 1 / 2 to 12 MPa·m 1 / 2 ). Therefore, the doping of lanthanum elements strengthens the interfacial binding energy between rare-earth elements and the WC matrix, improving the coating binding strength and toughness.

[0021] As a preferred technical solution of the present invention, the lanthanum salt in step (1) includes lanthanum nitrate; the cerium salt includes cerium nitrate; and the cobalt salt includes cobalt nitrate.

[0022] In the present application, the lanthanum salt, cerium salt, and cobalt salt are preferably nitrates, mainly using the characteristics of high solubility, easy reducibility, and no harmful residues of nitrates, which can ensure the optimal core-shell structure performance of the thermal spraying powder, thereby avoiding the influence of other anions on the final powder morphology and composition.

[0023] The tungsten salt includes any one or a combination of at least two of ammonium metatungstate, ammonium tungstate, or ammonium paratungstate. Typical but non-limiting examples of the combination are: a combination of ammonium metatungstate and ammonium tungstate, a combination of ammonium metatungstate and ammonium paratungstate, and a combination of ammonium tungstate and ammonium paratungstate.

[0024] The molar ratio of lanthanum element, cerium element, cobalt element, and tungsten element in the mixed slurry is (0.25 - 0.75):(0.25 - 0.75):(9.5 - 12.5):(86 - 90), such as 0.25:0.25:9.5:90, 0.3:0.3:10:89.4, 0.5:0.5:11:88, 0.75:0.75:12.5:86, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0025] The solvent in step (1) includes water; the pH of the mixed slurry is controlled at 3 - 4, such as 3.1, 3.2, 3.3, 3.4, 3.6, 3.8, 4.0, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0026] The lanthanum salt, cerium salt, cobalt salt, and tungsten salt are mixed with the solvent by stirring; the stirring time is 15 - 25 min, such as 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 22 min, 25 min, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0027] As a preferred technical solution of the present invention, the complexing agent in step (2) includes any one or a combination of at least two of citric acid, oxalic acid, or gluconic acid. Typical but non-limiting examples of the combination are: a combination of citric acid and oxalic acid, a combination of citric acid and gluconic acid, and a combination of oxalic acid and gluconic acid.

[0028] In the present invention, adding a complexing agent can form chelates with metal ions in the mixed slurry, making the lanthanum, cerium, cobalt, and tungsten metal ions uniformly mixed at the molecular scale, thereby avoiding the problem of nanoparticle aggregation caused by traditional ball milling.

[0029] The crosslinking agent includes any one or a combination of at least two of ethylene glycol, glutaraldehyde, or ethylene glycol diglycidyl ether. Typical but non-limiting examples of the combination are: a combination of ethylene glycol and glutaraldehyde, a combination of ethylene glycol and ethylene glycol diglycidyl ether, and a combination of glutaraldehyde and ethylene glycol diglycidyl ether.

[0030] The molar ratio of metal ions to complexing agent in the mixed slurry is 1:(2 - 5), such as 1:2, 1:3, 1:4, 1:5, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0031] The molar ratio of the complexing agent to the crosslinking agent is 1:(1.5 - 4), such as 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0032] The temperature of the stirring in step (2) is 80 - 90 °C, such as 80 °C, 82 °C, 84 °C, 86 °C, 88 °C, 90 °C, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0033] The time of the stirring is 3 - 4 h, such as 3 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h, 4.0 h, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0034] It should be noted that a complexing agent and a crosslinking agent are added to the mixed slurry and stirred until a blue sol is formed.

[0035] It should be noted that the gelation treatment is used to reduce the solvent in the mixed slurry; the gelation treatment can adopt the evaporation methods commonly used in the art, as long as the reduction of the solvent in the mixed slurry is achieved, such as methods of heating evaporation, vacuum rotary evaporation, etc.; the viscosity of the gel material is 500 mPa·s.

[0036] As a preferred technical solution of the present invention, the supercritical drying treatment in step (2) includes: after gradient replacement of the solvent in the gel material with a volatile solvent, drying treatment is carried out with a supercritical fluid, and then decompressed to atmospheric pressure to obtain a precursor material.

[0037] In the present invention, the supercritical drying treatment can eliminate the gas - liquid interface, maintain the porous structure of the precursor material, and avoid the problem that the porous structure is prone to collapse due to the existence of surface tension during conventional drying. By using a supercritical fluid to remove the solvent in the present invention, the collapse of the pores caused by the capillary force on the surface and inside of the powder particles can be avoided, thereby retaining the nanoscale uniformity of the precursor material.

[0038] It should be noted that before the gradient replacement, a pre - freezing treatment can be carried out; the pre - freezing treatment includes shaping the porous structure by cryogenically freezing the gel material.

[0039] The volatile solvent includes ethanol; the time for gradient displacement is 4 - 6 h, such as 4 h, 4.5 h, 5 h, 5.5 h, 6 h, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0040] The supercritical fluid includes carbon dioxide; the temperature for the drying treatment is 50 - 60 °C, such as 50 °C, 52 °C, 54 °C, 56 °C, 58 °C, 60 °C, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0041] The pressure for the drying treatment is at least 10 MPa, such as 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0042] The heating rate for the drying treatment is 1 - 1.5 °C / min, such as 1 °C / min, 1.1 °C / min, 1.2 °C / min, 1.3 °C / min, 1.4 °C / min, 1.5 °C / min, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0043] The time for the drying treatment is 1 - 3 h, such as 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0044] The rate of pressure reduction is 0.1 - 0.15 MPa / min, such as 0.1 MPa / min, 0.11 MPa / min, 0.12 MPa / min, 0.13 MPa / min, 0.14 MPa / min, 0.15 MPa / min, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0045] In the present invention, after the supercritical drying treatment, the specific surface area of the obtained precursor material particles is ≥ 300 m 2 / g, and the fine pore size distribution in the particles is 20 - 50 nm, which is beneficial to the subsequent reduction reaction.

[0046] As a preferred technical solution of the present invention, the plasma reduction treatment in step (3) is carried out in a mixed atmosphere of a first inert gas and a reducing gas.

[0047] In the present invention, the precursor material decomposes instantaneously in the plasma high-temperature zone, and the following reaction occurs:

[0048] ;

[0049] Through the in-situ plasma reduction reaction, the present invention forms a powder material with a core-shell structure, which has tungsten carbide as the core (particle size: 50 - 100 nm), and the outer shell layer is a powder co-deposited with La2O3 / CeO2 nanoparticles (particle size: 5 - 10 nm) and Co binder phase.

[0050] The plasma reduction treatment of the present invention can regulate the particle size of the powder material, and its empirical formula is:

[0051] ;

[0052] where P 等离子体 is the power of the plasma, in kW; V H2 / Ar is the volume ratio of the reducing gas to the first inert gas; R 进料 is the feed flow rate of the precursor material, in g / min.

[0053] The present invention adopts the plasma reduction process. Compared with the traditional sintering reduction process (reaction time requires several hours), the reaction time is greatly reduced (reaction time < 20 ms), and at the same time, the growth of grains is inhibited, making the size of tungsten carbide grains ≤ 100 nm; in addition, by adopting the plasma reduction process, the present invention enables the rare earth oxide and Co element to combine in the form of chemical bonds. Compared with the traditional process (interface energy ≥ 2 J / m 2 ), the preparation method of the present invention can reduce the interface energy to 0.8 J / m 2 ; and through the self-shaping of the plasma surface tension, the sphericity of the powder > 0.95, and the fluidity of the powder ≤ 15 s / 50 g.

[0054] The first inert gas includes any one or at least two combinations of argon, helium or nitrogen. Typical but non-limiting examples of the combinations are: the combination of argon and helium, the combination of argon and nitrogen, and the combination of helium and nitrogen.

[0055] The reducing gas includes hydrogen and / or carbon monoxide.

[0056] The power of the plasma is 45 - 55 kW, such as 45 kW, 46 kW, 47 kW, 48 kW, 49 kW, 50 kW, 52 kW, 55 kW, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0057] The power of the plasma defined by the present invention can ensure the full melting of the precursor material and improve the sphericity of the material; as the power of the plasma increases, the melting degree of the precursor material also increases, thereby improving the sphericity of the material, but too large a plasma power will cause an increase in the particle size of the material.

[0058] The flow rate of the first inert gas is 40 - 60 SLPM, such as 40 SLPM, 45 SLPM, 50 SLPM, 55 SLPM, 60 SLPM, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0059] The flow rate of the reducing gas is 10 - 15 SLPM, such as 10 SLPM, 11 SLPM, 12 SLPM, 13 SLPM, 14 SLPM, 15 SLPM, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0060] In the present invention, defining the flow rate ratio of the first inert gas to the reducing gas can reduce the size of tungsten carbide crystal nuclei. When the proportion of hydrogen increases, the reduction rate increases, resulting in a decrease in the size of tungsten carbide crystal nuclei.

[0061] The feeding flow rate of the precursor material is 3 - 10 g / min, such as 3 g / min, 4 g / min, 5 g / min, 6 g / min, 7 g / min, 8 g / min, 9 g / min, 10 g / min, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0062] In the present invention, the feeding flow rate of the precursor material affects the particle size of the material; when the feeding flow rate of the precursor material decreases, the residence time of the material increases, resulting in an increase in the particle size of the material.

[0063] The temperature of the plasma reduction treatment is 4000 - 6000 °C, such as 4000 °C, 4500 °C, 5000 °C, 5500 °C, 6000 °C, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0064] The time of the plasma reduction treatment is 10 - 20 ms, such as 10 ms, 12 ms, 14 ms, 16 ms, 18 ms, 20 ms, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0065] As a preferred technical solution of the present invention, the plasma reduction treatment in step (3) further includes a quenching treatment.

[0066] In the present invention, the quenching treatment can rapidly cool and inhibit grain growth, thereby locking the nanostructure of the material.

[0067] The quenching treatment is carried out using a second inert gas; the second inert gas includes helium and / or argon.

[0068] The flow rate of the second inert gas is 10 - 30 SLPM, such as 10 SLPM, 15 SLPM, 20 SLPM, 25 SLPM, 30 SLPM, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0069] The time of the quenching treatment is 8 - 10 s, such as 8 s, 8.5 s, 9 s, 9.5 s, 10 s, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0070] As a preferred technical solution of the present invention, the post-treatment described in step (3) includes pulsed electron beam irradiation treatment.

[0071] In the present invention, the pulsed electron beam irradiation treatment can instantaneously melt the powder surface layer (≈2 μm), and the surface nano-fine particles are closely agglomerated and rapidly solidified upon cooling to form a dense shell. At the same time, under the driving of the temperature gradient, lanthanum and cerium elements undergo thermophoretic migration in the liquid phase, thereby forming a rare earth-rich surface layer, while the rare earth element concentration distribution inside decreases in a gradient manner.

[0072] The energy density of the pulsed electron beam irradiation treatment is 2 - 5 J / cm 2 , such as 2 J / cm 2 , 2.5 J / cm 2 , 3 J / cm 2 , 3.5 J / cm 2 , 4 J / cm 2 , 4.5 J / cm 2 , 5 J / cm 2 etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0073] The pulse width is 1 - 3 μs, such as 1 μs, 1.5 μs, 2 μs, 2.5 μs, 3 μs, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0074] The number of pulses is 4 - 7 times, such as 4 times, 5 times, 6 times, 7 times, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0075] After the pulsed electron irradiation treatment, pneumatic sorting treatment is further included; the pneumatic sorting treatment is carried out by using a pneumatic sorting device; the air flow velocity of the pneumatic sorting device is 8 - 12 m / s; the centrifugal rotation speed of the pneumatic sorting device is 1500 - 3000 RPM.

[0076] The target particle size of the pneumatic sorting treatment is 20 - 30 μm.

[0077] It should be noted that in the pneumatic sorting process, powders smaller than 20μm are returned to the plasma reaction device for regranulation, while particles larger than 30μm are mechanically crushed and then sorted again.

[0078] In a second aspect, the present invention provides a rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder, which is prepared by the preparation method described in the first aspect.

[0079] In a third aspect, the present invention provides an application of the thermal spraying powder described in the second aspect, and the application includes preparing a metal wear-resistant coating using the thermal spraying powder.

[0080] The preparation includes spraying the thermal spraying powder on the surface of the substrate using a supersonic flame spraying device to form the metal wear-resistant coating.

[0081] Before the spraying, the surface of the substrate is also pretreated; the pretreatment is specifically: using 24-mesh white corundum sand, under a sandblasting pressure of 0.5 MPa, sandblasting the substrate to make the roughness of the substrate 6-8; then cleaning with an alkaline solution with a pH of 10, at a temperature of 60°C, cleaning the substrate for 15 minutes, then rinsing with deionized water, and performing ultrasonic drying treatment with absolute ethanol.

[0082] The kerosene flow rate of the supersonic flame spraying device is 380 L / h; the oxygen flow rate is 850 L / h; the spraying distance is 180 mm; the powder feeding rate of the precursor powder is 40 g / min; the nitrogen flow rate is 12 SLPM, and the coating is prepared.

[0083] After the spraying is completed, the surface of the coating is also chemically passivated.

[0084] The chemical passivation treatment includes impregnating the coating with a passivation solution, and then performing cleaning and drying treatments; the passivation solution includes nitric acid and cerium nitrate.

[0085] The present invention generates a dense CeO2 passivation film on the surface of the coating through chemical passivation treatment, which can significantly improve the chloride ion corrosion resistance and acid medium erosion resistance of the coating.

[0086] Compared with the prior art, the present invention has at least the following beneficial effects:

[0087] (1) The present invention chelates a complexing agent and a cross-linking agent to prepare a precursor, realizing the molecular-level uniform mixing of lanthanum, cerium, cobalt, and tungsten elements, and combining with the plasma instantaneous high-temperature reduction process, enabling rare earth atoms to replace the W sites in the WC lattice, greatly improving the rare earth doping efficiency;

[0088] (2) Through plasma reaction kinetics regulation and pulsed electron beam shaping technology, the present invention realizes precise control of powder particle size (D50 = 25 ± 3 μm, span ≤ 1.2), while maintaining the core-shell structure and rare earth gradient distribution of the powder, breaking through the particle size-performance contradiction of traditional screening and ball milling processes;

[0089] (3) The coating of the present invention undergoes chemical passivation treatment. Utilizing the "cerium oxide - cobalt" synergistic passivation mechanism, the corrosion resistance of the coating to chloride ions and acidic media is improved; meanwhile, the formed Ce - Cr - O composite film increases the service life of the coating in acidic / salt spray environments to 3 - 5 times that of traditional coatings;

[0090] (4) The preparation method of the present invention cancels the traditional high - energy - consuming ball milling and vacuum sintering steps, adopts one - step plasma continuous production, and increases the production capacity to 20 kg / h (traditional process ≤ 5 kg / h); the cost is reduced, the comprehensive energy consumption and labor cost are reduced by 50%, and the rare earth utilization rate is increased from 80% to 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 It is a SEM picture of fine nano - WC particles and micropores coated with nano - rare earth La2O3 / CeO2 combined with Co layer.

[0092] Figure 2 It is a SEM picture of powder particles formed by co - doping WC - Co with nano - rare earth La2O3 / CeO2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0093] The technical solution of the present invention will be further described below in conjunction with the drawings and through specific embodiments. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the claimed rights of the present invention. The scope of protection of the present invention is subject to the claims.

[0094] Example 1:

[0095] This example provides a preparation method of rare earth La2O3 / CeO2 co - doped WC - Co thermal spraying powder, and the preparation method includes:

[0096] (1) Mix lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, cobalt nitrate hexahydrate, ammonium metatungstate with water to obtain a mixed slurry; the molar ratio of lanthanum element, cerium element, cobalt element and tungsten element in the mixed slurry is 0.25:0.25:9.5:90; the pH of the mixed slurry is controlled at 3;

[0097] (2) Citric acid and ethylene glycol are added to the mixed slurry. After stirring and mixing at 80 °C, gelation treatment is carried out to obtain a gel material; the molar ratio of metal ions to complexing agent in the mixed slurry is 1:2; the molar ratio of citric acid to ethylene glycol is 1:1.5;

[0098] After gradient replacement of the solvent in the gel material with ethanol for 4 h, supercritical drying treatment is carried out with liquid carbon dioxide. First, the pressure is increased to 10 MPa, and then the temperature is increased to 50 °C at a heating rate of 1 °C / min and held for 2 h; subsequently, the pressure is reduced to atmospheric pressure at a pressure reduction rate of 0.1 MPa / min to obtain a precursor material;

[0099] (3) The precursor material is subjected to plasma reduction treatment in a mixed atmosphere of argon and hydrogen; the power of the plasma is 45 kW; the flow rate of argon is 40 SLPM; the flow rate of hydrogen is 10 SLPM; the feeding rate of the precursor material is 3 g / min; the temperature of the plasma reduction treatment is 4000 °C; the time of the plasma reduction treatment is 10 ms;

[0100] After the plasma reduction treatment, quenching treatment is carried out with helium; the flow rate of helium is 10 SLPM; the time of the quenching treatment is 8 s;

[0101] After the quenching treatment, pulsed electron beam irradiation treatment is carried out; the energy density of the pulsed electron beam irradiation treatment is 2 J / cm 2 ; the pulse width is 1 μs; the number of pulses is 4 times to obtain the thermal spraying powder. The SEM pictures of the thermal spraying powder are as shown in Figure 1 and Figure 2 shown.

[0102] Example 2:

[0103] This example provides a preparation method of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder, and the preparation method includes:

[0104] (1) Lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, cobalt nitrate hexahydrate, ammonium metatungstate and water are mixed to obtain a mixed slurry; the molar ratio of lanthanum element, cerium element, cobalt element and tungsten element in the mixed slurry is 0.75:0.75:12.5:86; the pH of the mixed slurry is controlled to be 4;

[0105] (2) Citric acid and ethylene glycol are added to the mixed slurry. After stirring and mixing at 90 °C, gelation treatment is carried out to obtain a gel material; the molar ratio of metal ions to complexing agent in the mixed slurry is 1:5; the molar ratio of citric acid to ethylene glycol is 1:4;

[0106] After gradient replacement of the solvent in the gel material with ethanol for 6 h, liquid carbon dioxide is used, the pressure is increased to 15 MPa, and then the temperature is increased to 60 °C at a heating rate of 1.5 °C / min and held for 3 h; subsequently, the pressure is reduced to atmospheric pressure at a pressure reduction rate of 0.15 MPa / min to obtain a precursor material;

[0107] (3) The precursor material is subjected to plasma reduction treatment in a mixed atmosphere of argon and hydrogen; the power of the plasma is 55 kW; the flow rate of argon is 60 SLPM; the flow rate of hydrogen is 15 SLPM; the feeding rate of the precursor material is 10 g / min; the temperature of the plasma reduction treatment is 6000 °C; the time of the plasma reduction treatment is 20 ms;

[0108] After the plasma reduction treatment, quenching treatment is carried out using helium; the flow rate of helium is 30 SLPM; the time of the quenching treatment is 10 s;

[0109] After the quenching treatment, pulsed electron beam irradiation treatment is carried out; the energy density of the pulsed electron beam irradiation treatment is 5 J / cm 2 ; the pulse width is 3 μs; the number of pulses is 7 times to obtain the thermal spraying powder.

[0110] Comparative Example 1:

[0111] This comparative example provides a method for preparing a rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder, which is different from Example 1 in that in step (1), the lanthanum element is replaced with an equimolar ratio of scandium element, and the remaining preparation conditions are the same as those in Example 1.

[0112] Comparative Example 2:

[0113] This comparative example provides a method for preparing a rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder, which is different from Example 1 in that in step (1), the cerium element is replaced with an equimolar ratio of yttrium element, and the remaining preparation conditions are the same as those in Example 1.

[0114] Comparative Example 3:

[0115] This comparative example provides a method for preparing a rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder, which is different from Example 1 in that in step (1), the addition of the lanthanum element is omitted, and the lanthanum element is replaced with an equimolar ratio of cerium element, and the remaining preparation conditions are the same as those in Example 1.

[0116] Comparative Example 4:

[0117] This comparative example provides a method for preparing rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The difference from Example 1 is that in step (1), the addition of cerium element is omitted, and the cerium element is replaced by lanthanum element in an equimolar ratio, and the remaining preparation conditions are the same as those in Example 1.

[0118] Comparative Example 5:

[0119] This comparative example provides a method for preparing rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The difference from Example 1 is that in step (1), the raw materials are mixed by the traditional ball milling method, and step (2) is omitted, and the remaining preparation conditions are the same as those in Example 1.

[0120] Comparative Example 6:

[0121] This comparative example provides a method for preparing rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The difference from Example 1 is that in step (2), traditional vacuum drying treatment is used, and the remaining preparation conditions are the same as those in Example 1.

[0122] Comparative Example 7:

[0123] This comparative example provides a method for preparing rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The difference from Example 1 is that in step (3), traditional high-temperature calcination reduction treatment is used, and the remaining preparation conditions are the same as those in Example 1.

[0124] Application Example 1:

[0125] This application example provides an application of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application uses the thermal spraying powder prepared in Example 1 to prepare a metal wear-resistant coating;

[0126] The preparation includes using a supersonic flame spraying device to spray the thermal spraying powder prepared in Example 1 on the surface of the substrate to form the metal wear-resistant coating. The spraying process includes:

[0127] (1) Pretreatment and spraying treatment: Use 24-mesh white corundum sand to sandblast the substrate at a sandblasting pressure of 0.5 MPa to make the roughness of the substrate 6 - 8; then clean it with an alkaline solution with a pH of 10, clean the substrate at a temperature of 60 °C for 15 min, then rinse it with deionized water, and perform ultrasonic drying treatment with absolute ethanol;

[0128] The kerosene flow rate of the supersonic flame spraying device is 380 L / h; the oxygen flow rate is 850 L / h; the spraying distance is 180 mm; the powder feeding rate of the precursor powder is 40 g / min; the nitrogen flow rate is 12 SLPM to prepare the coating;

[0129] (2) Chemical passivation treatment: At 60 °C, immerse the coating in a mixed solution of 5% nitric acid and 2% cerium nitrate for 30 min; then soak it in a 5% sodium bicarbonate solution with a pH of 8 for 5 min; ultrasonically clean it with deionized water for 10 min, with an ultrasonic frequency of 40 kHz; after purging with nitrogen, dry it in vacuum at 80 °C for 1 h, and the vacuum degree is 10 -2 Pa.

[0130] Application Example 2:

[0131] This application example provides an application of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Example 2, and the remaining preparation conditions are the same as those in Application Example 1.

[0132] Application Example 3:

[0133] This application example provides an application of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Example 1. The difference from Application Example 1 is that the chemical passivation treatment described in step (2) is omitted, and the remaining preparation conditions are the same as those in Application Example 1.

[0134] Comparative Application Example 1:

[0135] This comparative application example provides an application of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Comparative Example 1, and the remaining preparation conditions are the same as those in Application Example 1.

[0136] Comparative Application Example 2:

[0137] This comparative application example provides an application of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Comparative Example 2, and the remaining preparation conditions are the same as those in Application Example 1.

[0138] Comparative Application Example 3:

[0139] This comparative application example provides an application of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Comparative Example 3, and the remaining preparation conditions are the same as those in Application Example 1.

[0140] Comparative Application Example 4:

[0141] This comparative application example provides an application of rare-earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Comparative Example 4, and the remaining preparation conditions are the same as those in Application Example 1.

[0142] Comparative Application Example 5:

[0143] This comparative application example provides an application of rare-earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Comparative Example 5, and the remaining preparation conditions are the same as those in Application Example 1.

[0144] Comparative Application Example 6:

[0145] This comparative application example provides an application of rare-earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Comparative Example 6, and the remaining preparation conditions are the same as those in Application Example 1.

[0146] Comparative Application Example 7:

[0147] This comparative application example provides an application of rare-earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. The application prepares a metal wear-resistant coating using the thermal spraying powder prepared in Comparative Example 7, and the remaining preparation conditions are the same as those in Application Example 1.

[0148] Performance Test:

[0149] (1) According to the test standards of ASTM G31-21 (immersion corrosion) and ASTM B117 (salt spray test), the corrosion resistance of the coatings prepared in Application Examples 1-3 and Comparative Application Examples 1-7 was tested;

[0150] The test conditions were as follows: The coatings were immersed in a 3.5 wt% NaCl solution at an immersion temperature of 35 °C for 2000 h to test the corrosion resistance and salt spray corrosion resistance of the coatings;

[0151] (2) The Vickers microhardness test method was used to test the hardness of the coatings prepared in Application Examples 1-3 and Comparative Application Examples 1-7;

[0152] (3) At 800 °C, the coatings prepared in Application Examples 1-3 and Comparative Application Examples 1-7 were subjected to high-temperature oxidation treatment to test the high-temperature oxidation resistance of the coatings;

[0153] (4) Using the ASTM C633 test method, the bonding strength between the coatings prepared in Application Examples 1-3 and Comparative Application Examples 1-7 and the substrate was tested, and the test results are shown in Table 1.

[0154] Table 1

[0155]

[0156] It can be seen from the test results that:

[0157] (1) It can be seen from Application Examples 1-2 that the thermal spraying powder prepared by the present invention can significantly improve the high-temperature oxidation resistance and salt spray corrosion resistance of the coating, and at the same time can also improve the bonding strength and hardness of the coating;

[0158] In addition, from the SEM images of Figure 1 and Figure 2 it can be known that through the precursor chemical synthesis process, the atomic-level dispersion of rare earth elements and the directional doping of WC lattice are successfully realized. The rare earth elements La and Ce are combined with Co element in the form of La2O3 / CeO2 and are coated and distributed on the surface of the WC-core nanoparticles; through the plasma reduction treatment, the particle size of the material is regulated while maintaining the core-shell structure of the material and the gradient distribution of rare earth elements on the surface of fine particles, and at the same time the powder material is spheroidized by plasma, breaking through the particle size-performance contradiction of the traditional screening / milling process. Therefore, the thermal spraying powder prepared by the present invention has a high sphericity and uniform particle size, which is beneficial to the preparation of wear-resistant coatings with extremely high oxidation resistance and corrosion resistance;

[0159] (2) It can be seen from the comparison between Application Example 1 and Application Example 3 that by chemically passivating the coating of the present invention, a dense CeO2 passivation film is formed on the coating surface, which can significantly improve the chloride ion corrosion resistance and acid medium erosion resistance of the coating, so that the service life of the coating in an acidic / salt spray environment can be increased to 3-5 times that of the traditional coating;

[0160] (3) It can be seen from the comparison between Application Example 1 and Comparative Application Examples 1-4 that doping with lanthanum elements can improve the high-temperature oxidation resistance and bonding strength of the coating, and doping with cerium elements can improve the salt spray corrosion resistance of the coating; while in Comparative Application Examples 1-4, replacing or omitting lanthanum elements and cerium elements cannot improve the high-temperature oxidation resistance and salt spray corrosion resistance of the coating;

[0161] (4) It can be seen from the comparison between Application Example 1 and Comparative Application Example 5 that the present invention adopts the process of precursor chemical synthesis to achieve the molecular-level uniform mixing of rare earth elements and tungsten carbide matrix, improve the rare earth doping efficiency, improve the high-temperature oxidation resistance, salt spray corrosion resistance and hardness of the coating, and at the same time reduce the preparation cost of the coating material;

[0162] (5) It can be seen from the comparison between Application Example 1 and Comparative Application Example 6 that through supercritical drying treatment, the thermal spraying powder of the present invention maintains a porous structure, avoiding the pore collapse caused by the capillary force on the surface and inside of the powder particles, thereby improving the high-temperature oxidation resistance, salt spray corrosion resistance, hardness and bonding strength of the coating prepared by using this powder.

[0163] (6) It can be seen from the comparison between Application Example 1 and Comparative Application Example 7 that through plasma reduction treatment, the present invention can regulate the particle size of the thermal spraying powder, reduce the reaction time, and improve the sphericity of the powder, thereby improving the bonding strength of the coating prepared by using this powder.

[0164] In summary, the present invention provides a preparation method and application of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder. Through the precursor chemical synthesis process, the atomic-level dispersion of rare earth elements and the directional doping of WC lattice are realized; through plasma reduction treatment, the particle size of the material is regulated while maintaining the core-shell structure of the material and the gradient distribution of rare earth elements, breaking through the contradiction between particle size and performance of the traditional screening / milling process; the coating prepared by using the thermal spraying powder prepared by the present invention has good high-temperature oxidation resistance, excellent resistance to chloride ion corrosion and acid medium erosion, and high hardness and bonding strength; the preparation method of the present invention reduces costs and improves production capacity at the same time, increasing the rare earth utilization rate from 80% to 99%.

[0165] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder, characterized in that, The preparation method includes the following steps: (1) Mixing a lanthanum salt, a cerium salt, a cobalt salt, and a tungsten salt with a solvent to obtain a mixed slurry; (2) Adding a complexing agent and a crosslinking agent to the mixed slurry, stirring and mixing, followed by gelation treatment to obtain a gel material; subsequently, supercritical drying treatment is carried out to obtain a precursor material; The supercritical drying treatment includes: after gradient replacement of the solvent in the gel material with a volatile solvent, drying treatment is carried out using a supercritical fluid, and then the pressure is reduced to atmospheric pressure to obtain a precursor material; The volatile solvent includes ethanol; the time for gradient replacement is 4 - 6 h; The supercritical fluid includes carbon dioxide; the temperature of the drying treatment is 50 - 60 °C; the pressure of the drying treatment is at least 10 MPa; the heating rate of the drying treatment is 1 - 1.5 °C / min; the time of the drying treatment is 1 - 3 h; the rate of pressure reduction is 0.1 - 0.15 MPa / min; (3) Performing plasma reduction treatment and post-treatment on the precursor material to obtain the thermal spraying powder; the post-treatment in step (3) includes pulsed electron beam irradiation treatment; The plasma reduction treatment is carried out in a mixed atmosphere of a first inert gas and a reducing gas; the first inert gas includes any one or a combination of at least two of argon, helium, or nitrogen; the reducing gas includes hydrogen and / or carbon monoxide; The power of the plasma is 45 - 55 kW; the flow rate of the first inert gas is 40 - 60 SLPM; the flow rate of the reducing gas is 10 - 15 SLPM; the feeding flow rate of the precursor material is 3 - 10 g / min; the temperature of the plasma reduction treatment is 4000 - 6000 °C; the time of the plasma reduction treatment is 10 - 20 ms; The plasma reduction treatment further includes quenching treatment; the quenching treatment is carried out using a second inert gas; the second inert gas includes helium and / or argon; the flow rate of the second inert gas is 10 - 30 SLPM; the time of the quenching treatment is 8 - 10 s.

2. The preparation method according to claim 1, characterized in that, The lanthanum salt in step (1) includes lanthanum nitrate; the cerium salt includes cerium nitrate; the cobalt salt includes cobalt nitrate; The tungsten salt includes any one or a combination of at least two of ammonium metatungstate, ammonium tungstate, or ammonium paratungstate; The molar ratio of lanthanum element, cerium element, cobalt element, and tungsten element in the mixed slurry is (0.25 - 0.75):(0.25 - 0.75):(9.5 - 12.5):(86 - 90); The solvent in step (1) includes water; the pH of the mixed slurry is controlled at 3 - 4.

3. The preparation method according to claim 1, characterized in that, The complexing agent in step (2) includes any one or a combination of at least two of citric acid, oxalic acid, or gluconic acid; the crosslinking agent includes any one or a combination of at least two of ethylene glycol, glutaraldehyde, or ethylene glycol diglycidyl ether; The molar ratio of metal ions to the complexing agent in the mixed slurry is 1:(2 - 5); the molar ratio of the complexing agent to the crosslinking agent is 1:(1.5 - 4); The temperature of stirring in step (2) is 80 - 90 °C; the time of stirring is 3 - 4 h.

4. The preparation method according to claim 1, characterized in that, The energy density of the pulsed electron beam irradiation treatment is 2-5 J / cm 2 ; the pulse width is 1-3 μs; the number of pulses is 4-7 times.

5. A rare earth La2O3 / CeO2 co-doped WC-Co thermal spraying powder, characterized in that, The thermal spraying powder is prepared by the preparation method described in any one of claims 1-4.

6. Use of a thermal spray powder as described in claim 5, characterized in that, The application includes preparing a metal wear-resistant coating using the thermal spraying powder.

7. The application according to claim 6, wherein The preparation includes spraying the thermal spraying powder on the surface of a substrate using a supersonic flame spraying device to form the metal wear-resistant coating.

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