A preparation method of a WC enhanced composite coating

Abstract

The present invention discloses a preparation method of a WC-reinforced composite coating, which comprises the following steps: mixing ZrO2-WC composite powder and nickel-based alloy powder to obtain raw material powder; the ZrO2-WC composite powder and the nickel-based alloy powder have similar densities, and the ZrO2-WC composite powder is a core-shell structure particle formed by ZrO2 coating WC particles; using a laser cladding method to clad the raw material powder on the surface of a metal substrate to obtain a WC-reinforced composite coating. On the one hand, the present invention effectively avoids the decarburization and burning loss problems of WC during the laser cladding process through the protective effect of ZrO2 with a large heat generation generated by the external coating of the composite powder; in addition, the density of the composite WC-reinforced powder is close to that of the coating matrix, which can solve the problem of the WC-reinforced phase sinking and segregating in the laser molten pool caused by the too large density difference between the conventional WC-reinforced phase and the matrix, thereby obtaining a high-performance composite coating with no decarburization, burning loss of the WC-reinforced phase, uniform distribution, and no cracks in the composite coating.

Description

Technical Field

[0001] The present invention relates to a method for preparing a laser cladding coating, and particularly to a method for preparing a WC-reinforced composite laser cladding coating. Background Art

[0002] Tungsten carbide (WC) has a high melting point, high hardness and a low coefficient of thermal expansion. At the same time, it has good wettability with nickel-based alloys and is a commonly used ceramic reinforcement material for nickel-based alloys. Adding WC ceramic particle reinforcements to nickel-based alloy powders and fabricating metal matrix ceramic composite coatings by laser cladding can organically combine the strength and toughness of metals, good processability, and the excellent wear resistance, corrosion resistance, high temperature resistance and oxidation resistance of ceramic materials, and has potential application prospects.

[0003] During the process of laser cladding WC-reinforced composite coatings, there are mainly two problems: one is the decarburization and burning loss problems of WC; the other is that the density of WC is 15.63 g / cm 3 , far exceeding the density of the coating matrix material, and will sink to the bottom of the coating in the laser melt pool, resulting in uneven distribution of the coating structure. The brittle WC ceramic reinforcement phase aggregates near the interface to form stress concentration, which will induce the formation of coating cracks. The above two problems greatly affect the performance of the laser cladding WC-reinforced composite coating.

[0004] Therefore, it is necessary to control the decarburization, burning loss of WC during the laser cladding process and the problem of uneven distribution of WC in the composite coating, and provide a new method for laser cladding to prepare high-performance WC-reinforced composite coatings. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a method for preparing a WC-reinforced composite coating to solve the problem of how to prepare a high-performance WC-reinforced composite coating.

[0006] Technical Solution: A method for preparing a WC-reinforced composite coating according to the present invention includes the following steps:

[0007] S1. Mix the ZrO2-WC composite powder and nickel-based alloy powder evenly to obtain raw material powder; the ZrO2-WC composite powder and nickel-based alloy powder have the same density, and the ZrO2-WC composite powder is a core-shell structure particle formed by ZrO2 coating WC particles;

[0008] S2. Adopt the laser cladding method to clad the raw material powder on the surface of the metal substrate to obtain a WC-reinforced composite coating.

[0009] The present invention uses the ZrO2-WC composite powder as the reinforcement phase, and the composite powder and the matrix powder are mixed in a certain proportion as the cladding material for laser cladding to obtain a high-performance composite coating with no decarburization, burning loss of the WC reinforcement phase, uniform distribution, and no cracks in the composite coating.

[0010] Preferably, in step S1, the particle size of the ZrO2-WC composite powder is 10-100 μm, and the density is 8-9 g·cm -3 , where the volume ratio of ZrO2 to WC is 4-5:1.

[0011] The similar density of the ZrO2-WC composite powder and the matrix powder is achieved by adjusting the volume ratio of low-density ZrO2 to high-density WC in the composite powder.

[0012] Preferably, in step S1, the ZrO2-WC composite powder is prepared by the following method:

[0013] (1) Dissolve citric acid and polyvinylpyrrolidone in an ethylene glycol solution, and then sequentially add zirconium salt and WC particles, and stir well to obtain a mixed solution;

[0014] (2) Stir and heat the mixed solution, add n-butylamine after reaching the reaction temperature, and obtain a reactant after constant-temperature reaction;

[0015] (3) After cooling the reactant, centrifuge to obtain the precipitate, wash and dry to obtain the precursor product; the precursor product is spheroidized by radio frequency plasma to obtain the ZrO2-WC composite powder.

[0016] Preferably, in step (1), the zirconium salt includes at least one of zirconium nitrate, zirconium chloride, zirconium sulfate, zirconium oxalate, and zirconium carbonate, the mass ratio of the zirconium salt to the WC particles is 10-20:5-15, and the particle size of the WC particles is 1-3 μm.

[0017] Preferably, in step (1), the material ratio of citric acid, polyvinylpyrrolidone to ethylene glycol is 0.1-0.5 g:1.0-5.0 g:100-500 mL.

[0018] Preferably, in step (2), the conditions for stirring and heating are that the stirring speed is 300-500 r·min -1 , the heating rate is 3-5 °C·min -1 , the reaction temperature is 170-210 °C, and the constant-temperature reaction time is 3-5 h; the volume ratio of the n-butylamine to the ethylene glycol is 5-25:100-500.

[0019] Preferably, in step (3), the parameters of radio frequency plasma spheroidization are: the plasma power is 38-42 kW, the central gas flow rate is 15-25 L·min -1 , the Ar flow rate in the sheath gas is 40-60 L·min -1 , the H2 flow rate in the sheath gas is 20-28 L·min -1 , the carrier gas flow rate is 6-12 L·min -1, the powder feeding rate is 0.3 - 0.7 g·min -1 , and the system pressure is 12 - 18 kPa.

[0020] Preferably, in step S1, the mass ratio of the ZrO2-WC composite powder to the nickel-based alloy powder is 1 - 3:2 - 4, and the nickel-based alloy powder includes at least one of Ni 625 powder, Ni 718 powder, Ni C-276 powder, Ni X-750 powder, and Ni 690 powder.

[0021] Preferably, in step S2, the laser cladding method is: using a coaxial powder feeding multi-pass overlapping cladding process, the laser power is 1700 - 1900 W, the laser scanning speed is 400 - 440 mm·min -1 , the powder feeding speed is 2.0 - 2.2 r·min -1 , the spot diameter is 3 - 5 mm, the overlapping rate is 45 - 55%, and an inert gas is introduced during the cladding process. The inert gas can be argon, helium, nitrogen, etc.

[0022] Preferably, in step S2, the metal substrate is first polished to remove the oxide scale before the cladding operation, then the surface of the metal substrate is polished with sandpaper, and the surface oil stains and impurities of the metal substrate are cleaned with anhydrous ethanol and dried before being used for the cladding operation.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0024] The present invention uses the ZrO2-WC composite powder as the reinforcing phase and mixes it with the matrix powder in a certain proportion as the cladding material for laser cladding. On the one hand, the protective effect of ZrO2 with a large heat of formation in the ZrO2-WC composite powder avoids the decarburization and burning loss of WC during the laser cladding process. On the other hand, by adjusting the volume ratio of low-density ZrO2 to high-density WC in the composite powder, the density of the composite powder is made close to that of the matrix powder, effectively avoiding the too large density difference between the conventional WC reinforcing phase and the matrix, which will sink to the bottom of the coating in the laser molten pool, resulting in uneven tissue distribution. The brittle WC ceramic reinforcing phase aggregates near the interface to form stress concentration, which will induce the formation of coating cracks. A high-performance composite coating with uniform distribution of the reinforcing phase and no cracks in the composite coating is obtained. Description of the Drawings

[0025] Figure 1 is the SEM morphology of the Ni625 powder used in the present invention;

[0026] Figure 2 is the external SEM morphology of the ZrO2-WC composite powder used in Example 1;

[0027] Figure 3SEM morphology of the internal part of the ZrO2-WC composite powder used in Example 1;

[0028] Figure 4 XRD analysis results of the laser-cladded ZrO2-WC reinforced Ni625 composite coating in Example 1;

[0029] Figure 5 Low-magnification SEM morphology of the laser-cladded ZrO2-WC reinforced Ni625 composite coating in Example 1;

[0030] Figure 6 High-magnification SEM morphology of the laser-cladded ZrO2-WC reinforced Ni625 composite coating in Example 1;

[0031] Figure 7 SEM morphology of the laser-cladded ZrO2+WC reinforced Ni625 composite coating in Comparative Example 1. Detailed implementation manners

[0032] The technical solutions of the present invention will be further described below with reference to the accompanying drawings.

[0033] Example 1: A preparation method of a WC-reinforced composite coating includes the following steps:

[0034] (1) Dissolve 0.3 g of citric acid and 3.0 g of polyvinylpyrrolidone in 300 mL of ethylene glycol solution, then successively add 15 g of zirconium nitrate and 10 g of WC particles with a particle size of 1-3 μm, and stir for 45 min to obtain a mixed solution; subsequently transfer the mixed solution to a three-necked flask, set the stirring speed of the heating magnetic stirrer to 400 r·min -1 and the heating rate to 4 °C·min -1 . After reaching the reaction temperature of 190 °C, add 15 mL of n-butylamine, and react at a constant temperature for 4 h to obtain a reaction product; remove the reaction product from the heating device and cool it. Centrifuge and wash the cooled reaction product 4 times with absolute ethanol, and dry it in a vacuum drying oven at 90 °C for 8 h to obtain a precursor product; finally, use a radio frequency plasma spheroidization device of model TekSphero-40 produced by TEKNA Company of Canada, and process the precursor product according to the process shown in Table 1 to obtain the ZrO2-WC composite powder. The external SEM morphology of the ZrO2-WC composite powder is as Figure 2 shown, and the powder is also spherical, with a particle size of about 10-100 μm. The internal SEM morphology of the ZrO2-WC composite powder is as Figure 3 shown. The composite powder is composed of many WC particles with a size of 1-3 μm and a ZrO2 protective layer coated on the surface of the WC particles. Screen the ZrO2-WC composite powder within the size range required for laser cladding. The volume ratio of low-density ZrO2 to high-density WC in the ZrO2-WC composite powder is between 4:1 and 5:1, and the density is 8-9 g·cm -3 .

[0035] Table 1 Radio frequency plasma spheroidization process parameters

[0036]

[0037]

[0038] (2) The ZrO2-WC composite powder and Ni625 powder (Jiangsu Guoyi Special Alloy Co., Ltd.) were mechanically mixed evenly according to the mass ratio of 2:3 to obtain the raw material powder; in this embodiment, the density of the ZrO2-WC composite powder is the same as or close to that of the Ni625 powder. The ZrO2-WC composite powder is a core-shell structure particle formed by ZrO2 coating WC particles; the SEM morphology of the Ni625 powder is as Figure 1 shown, the powder is spherical, and the particle size is about 20-60 μm.

[0039] (3) The raw material powder was cladded on the surface of the metal substrate by laser cladding method, specifically:

[0040] 316L stainless steel with a size of 100mm×100mm×10mm was used as the metal substrate, and the raw material powder was used as the cladding material for the composite coating. Before cladding, the oxide scale on the surface of the metal substrate was removed with an angle grinder, then polished with sandpaper, and finally the surface oil stains and impurities were cleaned with anhydrous ethanol and dried. The cladding operation was carried out using the LDF6000 fiber-coupled semiconductor laser of LASERLINE Company in Germany and the KAWASAKI robot to prepare the ZrO2-WC particle-reinforced Ni625 composite coating specimen. The coaxial powder feeding multi-pass overlapping cladding process was adopted, the laser power was 1800W, the laser scanning speed was 420mm·min -1 , the powder feeding speed was 2.1r·min -1 , the spot diameter was 4mm, the overlapping rate was 50%, and 20L·min -1 argon gas was introduced as the protective gas during the test.

[0041] Figure 4 This is the XRD analysis result of the laser cladded ZrO2-WC reinforced Ni625 composite coating prepared in this embodiment. The coating is mainly composed of γ-Ni solid solution, ZrO2 and WC, and no W2C, M 23 C6 and other phase substances other than WC were detected in the conventional laser cladded WC reinforced composite coating, indicating that due to the protection of ZrO2 with a large heat of formation, the WC of the ZrO2-WC composite powder did not decarburize and burn during the laser cladding process.

[0042] Figure 5 and Figure 6They are the low-magnification and high-magnification SEM morphologies of the laser-clad ZrO2-WC reinforced Ni625 composite coating. It can be seen from the figure that due to the similar densities of the ZrO2-WC composite powder and the Ni625 matrix powder, it effectively avoids the too large density difference between the conventional WC reinforcing phase and the matrix phase, which will sink to the bottom of the coating in the laser melt pool, resulting in uneven tissue distribution. The brittle WC ceramic reinforcing phase aggregates near the interface to form stress concentration, which will induce the formation of coating cracks. A high-performance WC-reinforced composite coating with uniform distribution of the reinforcing phase and no cracks in the composite coating is obtained.

[0043] Example 2: The rest are the same as those in Example 1, except that:

[0044] Zirconium nitrate is replaced by zirconium chloride; the mass ratio of zirconium chloride to WC particles is 10:5;

[0045] The material ratio of citric acid, polyvinylpyrrolidone to ethylene glycol is 0.1 g·1.0 g·100 mL. The conditions for stirring and heating are that the stirring speed is 300 r·min -1 , and the heating rate is 3 °C·min -1 , the reaction temperature is 170 °C, and the constant-temperature reaction time is 3 h; the dosage of n-butylamine is 5 mL.

[0046] The parameters of radio frequency plasma spheroidization are: the plasma power is 38 kW, the central gas flow rate is 15 L·min -1 , the Ar flow rate in the sheath gas is 40 L·min -1 , the H2 flow rate in the sheath gas is 20 L·min -1 , the carrier gas flow rate is 6 L·min -1 , the powder feeding rate is 0.3 g·min -1 , and the system pressure is 12 kPa.

[0047] Ni 625 powder is replaced by Ni 690 powder, and the mass ratio of the ZrO2-WC composite powder to the Ni 690 powder is 1:2;

[0048] In the laser cladding operation, the laser power is 1700 W, the laser scanning speed is 400 mm·min -1 , the powder feeding speed is 2.0 r·min -1 , the spot diameter is 3 mm, and the overlap rate is 45%.

[0049] Example 3: The rest are the same as those in Example 1, except that:

[0050] Zirconium nitrate is replaced by zirconium oxalate; the mass ratio of zirconium oxalate to WC particles is 20:15;

[0051] The material ratio of citric acid, polyvinylpyrrolidone and ethylene glycol is 0.5 g·5.0 g·500 mL. The conditions for stirring and heating are that the stirring speed is 500 r·min -1 , and the heating rate is 5℃·min -1 , the reaction temperature is 210℃, and the constant temperature reaction time is 5 h; the dosage of n-butylamine is 25 mL.

[0052] The parameters of radio frequency plasma spheroidization are: the plasma power is 42 kW, the central gas flow rate is 25 L·min -1 , the Ar flow rate in the sheath gas is 60 L·min -1 , the H2 flow rate in the sheath gas is 28 L·min -1 , the carrier gas flow rate is 12 L·min -1 , the powder feeding rate is 0.7 g·min -1 , and the system pressure is 18 kPa.

[0053] Replace the Ni 625 powder with Ni 718 powder, and the mass ratio of the ZrO2-WC composite powder to the Ni 718 powder is 3:4;

[0054] In the laser cladding operation, the laser power is 1900 W, the laser scanning speed is 440 mm·min -1 , the powder feeding speed is 2.2 r·min -1 , the spot diameter is 5 mm, and the overlapping rate is 55%.

[0055] Example 4: The rest is the same as Example 1, except that:

[0056] Replace zirconium nitrate with zirconium sulfate; replace Ni 625 powder with Ni C-276 powder;

[0057] Comparative Example 1: The rest is the same as Example 1, except that:

[0058] Mix 5.45 g of zirconia with a particle size of 20-50 μm and 15 g of WC particles with a particle size of 1-3 μm directly and evenly as the control composite powder. Use the control composite powder to replace the ZrO2-WC composite powder to prepare the composite coating.

[0059] Comparative Example 2: The rest is the same as Example 1, except that:

[0060] Use WC powder with a particle size of 1-3 μm to replace the ZrO2-WC composite powder to prepare the composite coating.

[0061] Perform XRD analysis on the composite coatings prepared in Examples 1-4 and Comparative Examples 1-2. According to whether there are W2C, M other than WC in the coating 23Judge whether decarburization and burning loss occur to WC during laser cladding for phases such as C6, etc. Meanwhile, measure the compressive strength of the coating, and the results are as follows:

[0062] Table 2 Influence of different composite powders on decarburization and burning loss of WC in the coating

[0063]

[0064]

[0065] The results in Table 2 show that only the core-shell structured ZrO2-WC composite powder can effectively avoid the decarburization and burning loss problems of WC during laser cladding, avoid the generation of cracks in the coating, and thus effectively improve the strength of the coating. In Comparative Example 1, after directly mixing ZrO2 and WC, ZrO2 and WC cannot form a complex, and both exist independently. ZrO2 cannot solve the problems of decarburization, burning loss and sinking of WC. As Figure 7 shown, therefore, cracks occur in the composite coating and the strength is much lower than that of Example 1.

Claims

1. A preparation method of a WC enhanced composite coating, characterized in that It includes the following steps: S1. Mix the ZrO2-WC composite powder and the nickel-based alloy powder to obtain a raw material powder; the ZrO2-WC composite powder and the nickel-based alloy powder have similar densities, and the ZrO2-WC composite powder is a core-shell structure particle formed by ZrO2 coating WC particles; S2. Use the laser cladding method to clad the raw material powder on the surface of the metal substrate to obtain a WC-reinforced composite coating; The density of the ZrO2-WC composite powder is 8-9 g·cm -3 .

2. The preparation method of the WC enhanced composite coating according to claim 1, characterized in that, In step S1, the particle size of the ZrO2-WC composite powder is 10-100 μm, and the volume ratio of ZrO2 to WC is 4-5:

1.

3. The preparation method of the WC enhanced composite coating according to claim 1, characterized in that, In step S1, the ZrO2-WC composite powder is prepared by the following method: (1) Dissolve citric acid and polyvinylpyrrolidone in an ethylene glycol solution, and then sequentially add zirconium salt and WC particles, and stir well to obtain a mixed solution; (2) Stir and heat the mixed solution, add n-butylamine after reaching the reaction temperature, and obtain a reactant after constant temperature reaction; (3) After cooling the reactant, centrifuge to obtain a precipitate, wash and dry to obtain a precursor product; The precursor product is spheroidized by radio frequency plasma to obtain a ZrO2-WC composite powder.

4. The preparation method of the WC enhanced composite coating according to claim 3, characterized in that, The zirconium salt includes at least one of zirconium nitrate, zirconium chloride, zirconium sulfate, zirconium oxalate, and zirconium carbonate. The mass ratio of the zirconium salt to the WC particles is 10-20:5-15, and the particle size of the WC particles is 1-3 μm.

5. The preparation method of the WC enhanced composite coating according to claim 3, characterized in that, The material ratio of citric acid, polyvinylpyrrolidone to ethylene glycol is 0.1-0.5 g:1.0-5.0 g:100-500 mL.

6. The preparation method of the WC enhanced composite coating according to claim 3, characterized in that, The conditions for stirring and heating are that the stirring speed is 300 - 500 r·min -1 , the heating rate is 3 - 5 ℃·min -1 , the reaction temperature is 170 - 210 ℃, and the constant temperature reaction time is 3 - 5 h; the volume ratio of n-butylamine to ethylene glycol is 5~25:100 - 500.

7. The preparation method of the WC enhanced composite coating according to claim 3, wherein The parameters of radio frequency plasma spheroidization are as follows: the plasma power is 38 - 42 kW, the central gas flow rate is 15 - 25 L·min -1 , the Ar flow rate in the sheath gas is 40 - 60 L·min -1 , the H2 flow rate in the sheath gas is 20 - 28 L·min -1 , the carrier gas flow rate is 6 - 12 L·min -1 , the powder feeding rate is 0.3 - 0.7 g·min -1 , and the system pressure is 12 - 18 kPa.

8. The preparation method of the WC enhanced composite coating according to claim 1, characterized in that, In step S1, the mass ratio of the ZrO2-WC composite powder to the nickel-based alloy powder is 1-3:2-4, and the nickel-based alloy powder includes at least one of Ni 625 powder, Ni718 powder, Ni C-276 powder, Ni X-750 powder, and Ni 690 powder.

9. The preparation method of the WC enhanced composite coating according to claim 1, characterized in that, In step S2, the laser cladding method is as follows: a coaxial powder feeding multi-pass overlapping cladding process is adopted, the laser power is 1700 - 1900 W, the laser scanning speed is 400 - 440 mm·min -1 , the spot diameter is 3 - 5 mm, the overlapping rate is 45 - 55%, and an inert gas is introduced during the cladding process.

10. The preparation method of the WC enhanced composite coating according to claim 1, characterized in that, In step S2, before the cladding operation, the metal substrate is polished to remove the oxide scale, then the surface of the metal substrate is polished with sandpaper, and the surface oil stain and impurities of the metal substrate are cleaned with anhydrous ethanol and dried before being used for the cladding operation.

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