Ni-based composite coating with high WC particle content and preparation method thereof

Abstract

The invention discloses a preparation method of a WC particle reinforced Ni-based composite coating, and relates to the technical field of composite coating processing. According to the process method, the problems of low WC particle content, decomposition and layering when the WC-containing composite coating is prepared through laser cladding are solved, and the Ni-based composite coating which is high in WC particle content, uniform in WC particle distribution and high in yield can be prepared. According to the composite coating and the preparation method thereof, the WC particles and the Ni-based alloy powder are mechanically alloyed through a synergistic process of mechanical ball milling (containing boron and chlorine additives) and laser cladding, so that the addition of the WC particles in the cladding composite powder is remarkably improved, the welding performance is improved, the yield of the WC particles is increased, and decomposition and layering of WC are inhibited. And through the post-weld heat treatment process, post-weld internal stress of the Ni-based matrix is eliminated, component segregation is improved, the toughness and impact resistance of the coating are improved, and the WC composite coating can be stably applied to the high-stress impact load working condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite coating processing, in particular to a preparation method and application of a high-WC-particle-content Ni-based composite coating. BACKGROUND

[0002] WC particle reinforced metal composite coating (referred to as WC composite coating) is a surface strengthening material for industrial equipment such as mining, agriculture, and cement. It is a composite material with WC particles as wear-resistant hard phase and metal as ductile binder phase matrix. The typical microstructure of the WC composite coating is a multiphase composite system. The WC hard phase bears the load preferentially during friction, effectively blocking the direct wear of the matrix by external abrasive particles. Therefore, the WC particles need to have a high proportion (volume fraction higher than 40%) in the coating structure to form a continuous, uniform, and dispersed three-dimensional wear-resistant structure, effectively blocking the direct wear of the matrix by external abrasive particles. Currently, the commonly used WC composite coating preparation techniques include laser cladding, plasma surfacing, and oxyacetylene surfacing. As known, WC particles belong to ceramic hard phase and remain solid during the cladding process. They are retained in the coating by being infiltrated and fixed by the molten metal matrix. When the mass fraction of WC particles in the cladding composite powder reaches 60%, the molten metal formed by the melting of the matrix powder has limited infiltration capacity. During the cladding process, WC particles can be observed to splash in the form of "stars", so the yield of WC particles in the coating is low, and it is difficult to obtain a composite coating with a WC particle volume fraction higher than 40%. In addition, WC particles are easily decomposed under the combined action of the heat source and the molten pool during the cladding process, further reducing the volume fraction of WC in the coating, and the decomposed W and C melt into the matrix, increasing the crack sensitivity of the coating and reducing the performance of the composite coating. Furthermore, the WC ceramic particles deteriorate the welding performance of the composite powder, and the formed molten metal has poor flowability and spreadability, so the coating is difficult to form a good interface with the base material, and the coating contains a large number of defects such as pores and micro-cracks. At the same time, the laser cladding WC composite coating has rapid heating and cooling, and has problems such as composition segregation and stress concentration. Therefore, it is an urgent problem in the industry to develop an advanced and stable composite coating with high WC content. SUMMARY

[0003] The present application provides a high-WC-particle-content Ni-based composite coating and a preparation method thereof. The volume fraction of WC in the composite coating can reach 40% to 60%. In this way, the high-hardness WC particles are uniformly and dispersedly embedded in the Ni alloy matrix. Once the coating is worn, the high-hardness WC particles protrude from the surface of the matrix to protect the matrix from abrasive wear. At the same time, by eliminating the internal stress of the Ni matrix and improving the composition segregation, the wear resistance and impact resistance of the coating are improved, the service life of the part is prolonged, and the replacement frequency is reduced.

[0004] To achieve the above object, the present application provides the following technical solutions:

[0005] A preparation method of a high WC particle content Ni-based composite coating, characterized in that the method comprises the following steps:

[0006] S1, preparation of laser cladding composite powder

[0007] The WC particles and the Ni-based alloy powder mixture, and the boron and chlorine additives added to the mixture are prepared by mechanical ball milling;

[0008] S2, substrate pretreatment

[0009] Remove oil stains and rust from the surface of the substrate and preheat;

[0010] S3, laser cladding treatment

[0011] Laser cladding composite coating is performed on the surface of the substrate;

[0012] S4, post-weld heat treatment

[0013] The laser cladding composite coating part is placed in a heat treatment furnace for heat treatment.

[0014] In step S1, the WC particles: irregular blocky WC particles are selected, high melting point (≥2400℃), high hardness (HV 0.1 ≥2000), particle size selected 140-200 mesh.

[0015] In step S1, the Ni-based alloy powder is composed of the following components (mass fraction): chromium Cr 8-12% (preferably 9-11%, more preferably 10-10.5%), cobalt Co 3-5% (preferably 3-4%, more preferably 3.5%), tungsten W 1-2% (preferably 1.2-1.8%, more preferably 1.4-1.6%), iron Fe <4% (preferably <3%, more preferably <1.5%), carbon C ≤0.4% (preferably 0.1-0.3%, more preferably 0.1-0.2%), boron B 1.2-1.8% (1.4-1.6%, more preferably 1.5%), silicon Si 3.5-4.5% (preferably 3.8-4.3%, more preferably 4.0-4.2%), the rest being Ni; oxygen content ≤0.04% (preferably ≤0.02%, more preferably ≤0.01%), powder flowability ≤16s / 50g (preferably ≤15s / 50g, more preferably ≤14s / 50g), loose bulk density ≥4.0g / cm 3 (optimally ≥4.3g / cm 3 , more preferably ≥4.5g / cm 3 ), powder particle size 120-270 mesh (preferably 140-240, more preferably 150-200).

[0016] In step S1, the composite powder is prepared by mechanical ball milling, and the composition and process parameters are as follows: (1) the mixed powder components (mass fraction): WC particles: 60% to 80% (preferably 65% to 75%, more preferably 70-73%), the balance being Ni-based alloy powder;

[0017] (2) Additives: Add 3% to 5% (preferably 3.5% to 4.5%, more preferably 4-4.2%) of a boron and chlorine-containing additive to the total mass of the mixed powder, and the additive components (mass fraction) are: 30% to 50% (preferably 35-45%, more preferably 40-42%) B2O3, 50% to 70% (preferably 55-65%, more preferably 60-62%) CaCl2;

[0018] (3) Ball milling process:

[0019] a) Ball-to-material mass ratio of 3:1 to 5:1, and the grinding material is stainless steel ball with a diameter of 3 to 6 mm;

[0020] b) Protective atmosphere: high-purity argon (molar purity ≥ 99.99%)

[0021] c) Sealed ball milling of the tank

[0022] d) Ball milling time: 8 to 16 hours (preferably 10 to 14 hours, more preferably 12-13 hours)

[0023] e) Rotation speed: 200 to 240 r / min (preferably 210 to 230 r / min, more preferably 220-225 r / min).

[0024] In step S1, the composite powder is prepared by mechanical ball milling of WC particles and Ni-based alloy powder to achieve mechanical alloying.

[0025] In step S2, the surface scale of the substrate is cleaned with 80# sandpaper, and the polished substrate is rinsed with petroleum ether or anhydrous ethanol to remove surface oil stains, and then placed in an oven at 140°C to 180°C (preferably 150°C to 170°C, more preferably 160°C) for 20 to 40 minutes (preferably 25 to 35 minutes, more preferably 30-33 minutes).

[0026] In step S3, the process parameters of the laser cladding are: laser power of 1400 to 2000 W (preferably 1500 to 1800 W, more preferably 1600-1700 W), spot size of 10 mm x 2 mm, scanning speed of 15 to 25 cm / min (preferably 18 to 23 cm / min, more preferably 20-22 cm / min), and powder feeding rate of 10 to 20 g / min (preferably 12 to 18 g / min, more preferably 15-16 g / min).

[0027] In step S4, the cladded part is put into a heat treatment furnace at 850-950°C (preferably 880-930°C, more preferably 900-910°C) for 120-150 min (preferably 130-140 min, more preferably 135-137 min) to eliminate the welding stress of the coating and improve the composition segregation of the coating.

[0028] The substrate is boron steel, die steel, stainless steel or low alloy steel.

[0029] The WC particles are irregular bulk WC prepared by melting and crushing, high melting point (≥2400°C), high hardness (HV 0.1 ≥2000), and particle size of 140-200 mesh. Compared with spherical WC particles, irregular bulk WC particles exhibit more excellent dispersion uniformity in a coating system with a high proportion of addition. Matching the particle size of 140-200 mesh, irregular bulk WC particles are more easily entrained and migrated in the melt convection during the cladding process, and the melt is more fully stirred, thereby reducing the occurrence of local agglomeration and achieving more uniform distribution. At the same time, due to the larger specific surface area of the bulk WC particles and the rougher surface, the mechanical alloying degree with the Ni-based alloy powder after the subsequent ball milling process is higher, which is beneficial to the improvement of the WC particle yield; in addition, the bulk WC particles adhere to more additives, and the weldability of the composite powder is better than that of the powder with the same proportion of spherical WC.

[0030] The substrate structure of the Ni-based alloy coating is determined by its composition. The addition of B element in the powder can reduce the alloy melting point and improve the wettability, but it is easy to react with Cr, W and other elements to form borides. These borides precipitate along the dendrites to form a network structure, which can reduce the toughness and impact resistance of the coating. Therefore, the B content in the present formulation is controlled at 1.2-1.8%, which can ensure the self-fluxing and wettability of the powder, and effectively inhibit the excessive precipitation of borides. The Si content in the powder is controlled at 3.5-4.5%, and the Si / B ratio is controlled at 1.9-3.75, which can ensure the powder to maintain good self-fluxing and weldability through the synergistic effect of Si and B, limit the number of network, reduce the cladding power, and reduce the WC decomposition caused by high power heat source. The C element added in the powder mainly improves the alloy hardness by precipitating carbides, but excessive carbides can significantly reduce the toughness of the material. During the cladding process, a small amount or part of the WC particles decompose, releasing free C into the matrix alloy, further exacerbating the precipitation of carbides and the deterioration of toughness. Therefore, the C content in the present formulation is controlled at ≤0.4%, which can ensure the hardness of the substrate and inhibit the excessive precipitation of carbides. The addition of 8-12% Cr and 1-2% W in the Ni-based alloy powder promotes the in-situ precipitation of blocky M2B, M2C and M7C3 type carbon and borides during the formation of the coating. These hard phases significantly strengthen the substrate hardness and enhance the wrapping and fixing effect of the substrate on the WC particles. The addition of 3-5% Co in the Ni-based alloy powder significantly improves the interfacial bonding between the WC particles and the Ni substrate. Fe element is easy to react with WC to form fishbone-like M6C, which indirectly promotes the decomposition of WC. Therefore, the Fe content in the present formulation is controlled at <4%.

[0031] The cladding composite powder adopts a mechanical ball milling powder mixing scheme. The WC particles and the Ni-based alloy powder are weighed according to the proportion, put into a ball milling tank, and 3-5% of a boron and chlorine containing additive is added, the ball-to-powder ratio is 4:1, the tank is filled with high-purity argon (99.99%), the tank is sealed, the ball milling time is 8-16h, and the ball milling speed is 200r / min. After mechanical ball milling, the WC particles and the Ni-based alloy form a mechanical metallurgical bond in the composite powder, which significantly improves the weldability and allows the upper limit of the WC addition ratio to be increased. At the same time, the addition of the boron and chlorine containing additive can remove the refractory oxides on the surface of the WC particles and the Ni-based powder, reduce the powder melting point and the melt viscosity, enhance the wettability of the Ni-based melt to the WC particles, and further improve the yield of WC particles in the composite coating.

[0032] Surface treatment of the substrate. Choose 80# sandpaper to clean the surface of the substrate, rinse the polished alloy with petroleum ether or anhydrous ethanol to remove surface oil and dirt, and then place it in an oven at 140-180°C for 20-40min.

[0033] In the laser cladding preparation method of the wear-resistant coating, the laser power is 1400-2000W, the spot size is 10mm*2mm, the scanning speed is 15-25cm / min, and the powder feeding rate is 10-20g / min.

[0034] The cladded part is placed in a heat treatment furnace at 850-950 DEG C for 120-150min, and then cooled in the furnace to eliminate the welding stress in the coating and improve the component segregation, thereby significantly improving the toughness and impact resistance of the coating.

[0035] Compared with the prior art, the present application has the beneficial effects that: through the synergistic process of mechanical ball milling (containing boron and chlorine additives) and laser cladding, the upper limit of WC particle addition in the cladding composite powder is significantly improved, the welding performance is improved, the WC decomposition and delamination are inhibited, and the yield of WC in the coating is improved, finally a Ni-based composite coating with a WC particle volume fraction of 40-60% is obtained, the technical bottleneck of preparing a composite coating with a WC volume fraction of <40% by laser cladding is broken, and the WC is uniformly and dispersedly embedded in the Ni alloy matrix, the wear resistance of the part is significantly improved (more than 3 times), and the service life is prolonged; through the post-weld heat treatment process, the internal stress after welding and the component segregation are eliminated, the toughness and impact resistance of the coating are improved, and the WC composite coating can be stably applied to high stress impact load working conditions. In addition, by improving the yield of WC particles, the utilization rate of the composite powder is improved, and the manufacturing cost of the composite coating is significantly reduced.

[0036] The present application solves the problems of low WC particle content, decomposition and delamination when preparing a WC-containing composite coating by laser cladding, and can prepare a Ni-based composite coating with high WC particle content, uniform distribution and high yield. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Friction and wear schematic diagram of the WC composite coating.

[0038] Figure 2WC particles and Ni-based alloy powder morphology, (a) WC particles (b) Ni-based alloy powder.

[0039] Figure 3 WC composite coating macro-morphology.

[0040] Figure 4 SEM micro-morphology of WC composite coating. DETAILED DESCRIPTION

[0041] The application will be described in further detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the application. These are within the scope of protection of the application

[0042] The high WC particle content Ni-based composite coating and its preparation method of the application will be described in detail below with reference to the accompanying drawings, as follows:

[0043] Comparative example

[0044] As shown in Figure 4 (a), the 60% WC-Ni-based composite coating without cladding by the technology of the application has a WC particle volume fraction of only 33%, and the distribution is uneven, with segregation at the bottom (close to the substrate side). Irregular blocky WC particles (produced by Zigong Great Wall Surface Engineering Technology Co., Ltd., high melting point (2525°C), high hardness (2200-2600 HV 0.1 ), particle size 140-200 mesh; Ni-based alloy powder was prepared by the gas mist method (Tianjin Chugang Technology Development Co., Ltd.), with the following composition (mass fraction): chromium Cr 8.62%, iron Fe 2.69%, carbon C 0.31%, boron B 2.02%, silicon Si 3.24%, and the rest being Ni. Oxygen content 0.01%, powder flowability 13.9 s / 50 g, bulk density 4.71 g / cm3, powder particle size 120-270 mesh;

[0045] Preparation of 60% WC-Ni-based composite powder: 1.2 kg of WC particles and 0.8 kg of Ni-based alloy powder were weighed and added to a ball mill tank, and 8 kg of milling media (diameter 3-6 mm stainless steel balls) was added. The tank was filled with high-purity argon (molar purity 99.99%) to displace the air inside, the tank was sealed, the mixing time was 2 h, and the rotation speed was 200 r / min.

[0046] Pre-treatment of the substrate: the substrate was a 34MnB5 steel plate with a thickness of 10 mm. The surface of the substrate was cleaned with 80# sandpaper to remove the oxide skin, the polished substrate was rinsed with petroleum ether to remove oil stains, and then placed in an oven for preheating. The preheating temperature was 140°C, and the preheating time was 20 min.

[0047] The composite powder was coated on the surface of the substrate by laser cladding. The process parameters of the laser cladding were as follows: laser power 1600 W, spot size 10 mm x 2 mm, scanning speed 25 cm / min, and powder feeding rate 15 g / min. The thickness of the composite coating was 0.5 mm.

[0048] The cladded part was placed in a heat treatment furnace at 850°C for 120 min, and then cooled to room temperature in the furnace to eliminate the welding stress in the coating and improve the composition segregation.

[0049] The composite coating test sample with a size of 10 mm x 10 mm (length x width, coating area) was prepared by electro-spark wire cutting. The cross-section of the sample (substrate with coating) was polished using 80 mesh, 150 mesh, 400 mesh, 800 mesh, and 1200 mesh metallographic sandpaper, respectively, and then polished on a polishing machine using 0.25 μm diamond polishing agent until the scratches on the surface of the sample (cross-section) disappeared. Finally, the sample was cleaned with deionized water to remove the polishing paste. Concentrated hydrochloric acid (HCl, mass concentration 36-38%) and concentrated nitric acid (HNO3, mass concentration 65-68%) were mixed in a volume ratio of 3:1 to prepare aqua regia. The polished composite coating sample was immersed in the aqua regia solution for 2 min, and then rinsed with deionized water and alcohol, respectively.

[0050] The microstructure of the coating was observed by scanning electron microscopy. The volume fraction of WC particles in the coating was measured using Image J software. The hardness of the coating was measured using a microhardness tester.

[0051] As shown in Figure 4 (a), the WC particle volume fraction of the 60% WC-Ni-based composite coating of the comparative example was only 33% (ignoring the differences in decomposition and powder yield, the theoretical volume fraction of WC was about 46%), the WC particle yield was 71%, and the distribution was uneven, with bottom segregation. The matrix hardness was about 460 HV 0.2 .

[0052] Example 1

[0053] The morphologies of the WC particles and the Ni-based alloy powder are shown in Figure 2 . Irregular blocky WC particles (produced by Zigong Great Wall Surface Engineering Technology Co., Ltd., high melting point (2525°C), high hardness (2200-2600 HV 0.1 ), particle size 140-200 mesh) were selected. The Ni-based alloy powder was prepared by gas atomization, and the composition was as follows (mass fraction): chromium Cr 8%, cobalt Co 3%, tungsten W 1%, iron Fe 3.5%, carbon C 0.22%, boron B 1.2%, silicon Si 3.6%, and the rest was Ni. The oxygen content was 0.03%, and the powder flowability was 13.5 s / 50 g, and the loose bulk density was 4.4 g / cm3 , powder particle size 120-270 mesh;

[0054] 60% WC-Ni based composite powder preparation: 1.2 kg of WC particles, 0.8 kg of Ni-based alloy powder, added to the ball mill tank, added 8 kg of abrasive (diameter 3-6 mm stainless steel ball), added 60 g of additives (20 g of B2O3, 40 g of CaCl2); the tank is filled with high-purity argon (molar purity 99.99%) to replace the air inside, seal the tank, ball milling time 8 h, ball milling speed 200 r / min. After mechanical ball milling, the oxide layer on the surface of the WC particles and the Ni alloy powder is stripped, exposing the fresh active surface, and the Ni alloy component diffuses to the WC particles, forming a mechanical metallurgical bond.

[0055] Pre-treatment of the substrate: the substrate is selected as a 10 mm thick 34MnB5 steel plate, the surface scale of the substrate is cleaned with 80# sandpaper, the polished substrate is rinsed with petroleum ether to remove oil stains, and then placed in an oven for preheating, the preheating temperature is 140°C, and the preheating time is 20 min.

[0056] Laser cladding coating composite powder on the surface of the substrate. The process parameters of the laser cladding are: laser power 1600 W, spot size 10 mm x 2 mm, scanning speed 25 cm / min, powder feeding rate 15 g / min. The thickness of the composite coating is 0.6 mm, and the macro-morphology is as shown in Figure 3 .

[0057] The cladded part is placed in a heat treatment furnace at 850°C for 120 min, and cooled to room temperature in the furnace to eliminate the welding stress in the coating and improve the composition segregation.

[0058] A test sample of 10 mm x 10 mm (length x width, coating area) of the substrate with the coating is prepared by wire electro-discharge machining, and the cross-section of the sample (substrate with coating) is polished with 80 mesh, 150 mesh, 400 mesh, 800 mesh, and 1200 mesh metallographic sandpaper, respectively, and then polished on a polishing machine using 0.25 μm diamond polishing agent until the scratches on the surface of the sample (cross-section) disappear. Finally, the sample is cleaned with deionized water to remove the polishing paste. Concentrated hydrochloric acid (HCl, mass concentration 36-38%) and concentrated nitric acid (HNO3, mass concentration 65-68%) are mixed in a volume ratio of 3:1 to prepare aqua regia, and the polished composite coating sample is immersed in the aqua regia solution for 2 min, and then rinsed with deionized water and alcohol.

[0059] The microstructure of the coating is observed by scanning electron microscopy; the volume fraction of the WC particles in the coating is measured by Image J software; and the hardness of the coating is measured by a microhardness tester.

[0060] As shown in Figure 4(b) As shown, the composite coating prepared by the present application, WC is uniformly distributed in the composite coating, and the original irregular block morphology is maintained, indicating that WC particles do not decompose a large amount during the coating preparation process; it is determined that the volume fraction of WC in the composite coating is 41% (ignoring the decomposition and powder yield difference, the theoretical volume fraction of WC is about 46%), the WC particle yield is 89%, and a continuous, uniformly dispersed anti-wear structure is formed, which ensures the wear resistance of the coating; WC particles and in-situ generated block or rod-shaped carbides, borides (M2C, M2B, M 23 C6, etc.) effectively block the formation of interdendritic eutectic network structure, improve the impact resistance of the coating; the hardness of the matrix is about 380HV 0.2 .

[0061] Example 2

[0062] Select irregular block WC particles (produced by Zigong Great Wall Surface Engineering Technology Co., Ltd., high melting point (2525℃), high hardness (2200-2600HV 0.1 ), particle size 140-200 mesh; use gas mist method to prepare Ni-based alloy powder, composition as follows (mass fraction): chromium Cr 10%, cobalt Co 4%, tungsten W 1.5%, iron Fe 2%, carbon C 0.35%, boron B 1.6%, silicon Si 3.0%, the rest is Ni. Oxygen content 0.02%, powder flowability 14.5s / 50g, loose density 4.5g / cm 3 , powder particle size 120-270 mesh;

[0063] 70%WC-Ni-based composite powder preparation: take 1.4kg WC particles, 0.6kg Ni-based alloy powder, add to the ball mill tank, add 9kg abrasive (diameter 3-6mm stainless steel ball), add 80g additive (30g B2O3, 50g CaCl2); the tank is filled with high-purity argon (molar purity 99.99%) to replace the air inside, seal the tank, ball milling time 12h, ball milling speed 220r / min. The composite powder obtained by mechanical ball milling, the oxide layer on the surface of WC particles and Ni alloy powder is stripped, exposing fresh active surface, Ni alloy components diffuse into WC particles, forming a mechanical metallurgical bond.

[0064] Preparation of the substrate: the substrate is a 12mm thick H13 steel plate, the surface oxide scale of the substrate is cleaned with 80# sandpaper, the polished substrate is rinsed with petroleum ether to remove oil stains, and then placed in an oven for preheating, the preheating temperature is 160℃, and the preheating time is 30min.

[0065] The composite powder is coated on the surface of the substrate by laser cladding. The process parameters of the laser cladding are as follows: the laser power is 1800 W, the spot size is 10 mm x 2 mm, the scanning speed is 20 cm / min, and the powder feeding rate is 10 g / min. The thickness of the composite coating is 0.4 mm, and the macro-morphology is shown in Figure 3 .

[0066] The cladded part is placed in 900℃ for 130 min, and then cooled to room temperature in the furnace to eliminate the welding stress and composition segregation in the coating.

[0067] The composite coating test sample with a size of 10 mm x 10 mm (length x width, coating area) is obtained by electro-spark wire cutting. The cross section of the sample (substrate with coating) is polished by using 80 mesh, 150 mesh, 400 mesh, 800 mesh and 1200 mesh metallographic sandpaper, respectively, and then polished on a polishing machine by using 0.25 μm diamond polishing agent until the scratches on the surface of the sample (cross section) disappear. Finally, the sample is cleaned by using deionized water to remove the polishing paste. Concentrated hydrochloric acid (HCl, mass concentration 36-38%) and concentrated nitric acid (HNO3, mass concentration 65-68%) are mixed in a volume ratio of 3:1 to prepare aqua regia. The polished composite coating sample is immersed in the aqua regia solution for 2 min, and then cleaned by using deionized water and alcohol, respectively. The microstructure of the sample is observed by using a scanning electron microscope, and the volume fraction of WC particles in the coating is measured by using Image J software.

[0068] As shown in Figure 4 (c), the WC particles are uniformly distributed in the composite coating prepared by the present application, and the original irregular block morphology is maintained, which indicates that the WC particles do not decompose in large quantities during the preparation of the coating. The volume fraction of WC in the composite coating is 48% (ignoring the difference in decomposition and powder yield, the theoretical volume fraction of WC is 47%), and a continuous and uniformly dispersed wear-resistant structure is formed, which ensures the wear resistance of the coating. The WC particles and the in-situ generated block or rod-shaped carbides and borides (M2C, M2B, M 23 C6, etc.) effectively block the formation of a network structure of interdendritic eutectic structure, and improve the impact resistance of the coating. The hardness of the substrate is about 510 HV 0.2 .

[0069] Example 3

[0070] Irregular block-shaped WC particles (produced by Zigong Great Wall Surface Engineering Technology Co., Ltd., high melting point (2525℃), high hardness (2200-2600 HV 0.1), particle size 140-200 mesh; Ni-based alloy powder was prepared by gas atomization method, and the composition (mass fraction) was as follows: chromium Cr 12%, cobalt Co 5%, tungsten W 1.2%, iron Fe 1.0%, carbon C 0.4%, boron B 1.8%, silicon Si 4.4%, and the balance was Ni. The oxygen content was 0.01%, the powder flowability was 15.0 s / 50 g, the loose bulk density was 4.27 g / cm3, and the powder particle size was 120-270 mesh;

[0071] 80% WC-Ni-based composite powder preparation: 1.6 kg of WC particles and 0.4 kg of Ni-based alloy powder were weighed and added to a ball mill tank, 10 kg of grinding material (diameter 3-6 mm stainless steel ball) was added, and 100 g of additive (50 g of B2O3, 50 g of CaCl2) was added; the tank was filled with high-purity argon (molar purity 99.99%) to replace the air therein, the tank was sealed, the ball milling time was 16 h, and the ball milling speed was 240 r / min. After mechanical ball milling, the oxide layer on the surface of the WC particles and the Ni alloy powder was stripped, exposing the fresh active surface, the Ni alloy component diffused into the WC particles, and a mechanical metallurgical bond was formed.

[0072] Pre-treatment of the substrate. The substrate was a 8 mm thick 304 steel plate, the surface scale of the substrate was cleaned with 80# sandpaper, the polished substrate was rinsed with petroleum ether to remove oil stains, and then placed in an oven for preheating, the preheating temperature was 180℃, and the preheating time was 40 min.

[0073] Laser cladding coating composite powder on the surface of the substrate. The process parameters of the laser cladding were as follows: laser power was 2000 W, spot size was 10 mm x 2 mm, scanning speed was 15 cm / min, and powder feeding rate was 20 g / min. The thickness of the composite coating was 0.8 mm, and the macroscopic morphology was as shown in Figure 3 .

[0074] The cladded part was placed in a furnace at 950℃ for 14 min, and then cooled to room temperature, which eliminated the welding stress in the coating and improved the composition segregation.

[0075] The composite coating test sample of 10 mm x 10 mm (length x width, coating area) of the base material with a coating layer is polished on the cross section by using 80 mesh, 150 mesh, 400 mesh, 800 mesh and 1200 mesh metallographic sandpaper in sequence, and then polished on a polishing machine by using 0.25 μm diamond polishing agent until the scratches on the surface of the sample (cross section) disappear, and finally the sample is cleaned with deionized water to remove the polishing paste. Concentrated hydrochloric acid (HCl, mass concentration 36-38%) and concentrated nitric acid (HNO3, mass concentration 65-68%) are mixed to prepare aqua regia with a volume ratio of 3:1, and the polished composite coating sample is immersed in the aqua regia solution for 2 min, and then washed with deionized water and alcohol in sequence. The microstructure morphology of the sample is observed by using a scanning electron microscope, and the volume fraction of the WC particles in the coating layer is measured by using Image J software.

[0076] As shown in Figure 4 (d), the composite coating layer prepared by using the present technology is uniformly distributed with WC, and the original irregular block morphology is maintained, which indicates that the WC particles do not decompose in large quantities during the preparation of the coating layer; it is determined that the volume fraction of WC in the composite coating layer is 56% (ignoring the difference in decomposition and powder yield, the theoretical volume fraction of WC is 69%), and a continuous and uniformly dispersed wear-resistant structure is formed, which ensures the wear resistance of the coating layer; the WC particles and the in-situ generated block or rod-shaped carbide and boride (M2C, M2B, M 23 C6, etc.) effectively block the formation of a network structure of interdendritic eutectic structure, and improve the impact resistance of the coating layer; the hardness of the matrix is about 630 HV 0.2 .

Claims

1. A method for preparing a Ni-based composite coating with high WC particle content, characterized in that, Includes the following steps: S1. Preparation of cladding composite powder Prepared by mechanical ball milling of a mixture of WC particles and Ni-based alloy powder, and boron- and chlorine-containing additives added to the mixture; S2, Substrate Pretreatment Remove oil and rust from the substrate surface and preheat; S3, Laser Cladding Process Laser cladding composite coating is applied to the surface of the substrate; S4. Post-weld heat treatment The parts with the clad composite coating are placed in a heat treatment furnace for heat treatment.

2. The preparation method according to claim 1, characterized in that, In step S1, WC particles: irregular blocky WC particles with high melting point (≥2400℃) and high hardness (HV) are selected. 0.1 ≥2000), with a particle size of 140-200 mesh.

3. The preparation method according to claim 1, characterized in that, In step S1, the Ni-based alloy powder is composed of the following components (mass fraction): Chromium (Cr) 8-12% (preferably 9-11%, more preferably 10-10.5%), Cobalt (Co) 3-5% (preferably 3-4%, more preferably 3.5%), Tungsten (W) 1-2% (preferably 1.2-1.8%, more preferably 1.4-1.6%), Iron (Fe) <4% (preferably <3%, more preferably <1.5%), Carbon (C) ≤0.4% (preferably 0.1-0.3%, more preferably 0.1-0.2%), Boron (B) 1.2-1.8% (1.4-1.6%, more preferably 1.5%), and Silicon (Si). 3.0–4.5% (preferably 3.8–4.3%, more preferably 4.0–4.2%), the remainder being Ni; oxygen content ≤0.04% (preferably ≤0.02%, more preferably ≤0.01%), powder flowability ≤16s / 50g (preferably ≤15s / 50g, more preferably ≤14s / 50g), and loose density ≥4.0g / cm³. 3 (Preferred size ≥4.3g / cm³) 3 More preferably ≥4.5g / cm 3 The powder particle size is 120-270 mesh (preferably 140-240, more preferably 150-200).

4. The preparation method according to claim 1, characterized in that, In step S1, the composite powder is prepared by mechanical ball milling, and its composition and process parameters are as follows: (1) Mixed powder composition (mass fraction): WC particles: 60% to 80% (preferably 65% ​​to 75%, more preferably 70% to 73%), balance Ni-based alloy powder; (2) Additives: Add 3% to 5% (preferably 3.5% to 4.5%, more preferably 4-4.2%) of boron- and chlorine-containing additives to the total mass of the mixed powder. The additive components (mass fraction) are: 30% to 50% (preferably 35% to 45%, more preferably 40-42%) of B2O3 and 50% to 70% (preferably 55% to 65%, more preferably 60-62%) of CaCl2. (3) Ball milling process: a) The ball-to-material mass ratio is 3:1 to 5:1, and the abrasive is a stainless steel ball with a diameter of 3 to 6 mm; b) Protective atmosphere: High-purity argon (molar purity ≥ 99.99%) c) Tank sealing ball mill d) Ball milling time: 8 to 16 hours (preferably 10 to 14 hours, more preferably 12 to 13 hours) e) Rotation speed: 200 to 240 r / min (preferably 210 to 230 r / min, more preferably 220 to 225 r / min).

5. The preparation method according to claim 1, characterized in that, In step S1, the composite powder is mechanically alloyed with WC particles and Ni-based alloy powder by mechanical ball milling.

6. The preparation method according to claim 1, characterized in that, In step S2, select 80# sandpaper to clean the oxide scale on the surface of the substrate, rinse the sanded substrate with petroleum ether or anhydrous ethanol to remove surface oil, and then place it in an oven at 140℃~180℃ (preferably 150℃~170℃, more preferably 160℃) for 20~40min (preferably 25~35min, more preferably 30-33min).

7. The preparation method according to claim 1, characterized in that, In step S3, the laser cladding process parameters are as follows: laser power of 1400-2000W (preferably 1500-1800W, more preferably 1600-1700W), spot size of 10mm×2mm, scanning speed of 15-25cm / min (preferably 18-23cm / min, more preferably 20-22cm / min), and powder feeding rate of 10-20g / min (preferably 12-18g / min, more preferably 15-16g / min).

8. The preparation method according to claim 1, characterized in that, In step S4, the clad component is placed in a heat treatment furnace at 850℃~950℃ (preferably 880℃~930℃, more preferably 900-910℃) and held for 120min~150min (preferably 130min~140min, more preferably 135-137min) and then cooled to room temperature to eliminate welding stress in the coating and improve the compositional segregation of the coating.

9. The preparation method according to claim 1, characterized in that, The substrate is boron steel, mold steel, stainless steel or low alloy steel.

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