Laser remelting of rare earth modified WC-10Ni coating and method of making the same

Abstract

The application discloses a laser remelting rare earth modified WC-10Ni coating and a preparation method thereof, and relates to the technical field of tungsten carbide alloy modification. The application solves the problem that the high-performance requirement of a water turbine flow part cannot be met by a supersonic flame spraying preparation process. The method comprises the following steps: pretreating a 0Cr13Ni5Mo martensitic stainless steel base body; preparing a rare earth modified WC-10Ni coating on the surface of the base body by using a supersonic flame spraying technology; and then performing laser remelting treatment under the protection of inert gas, and performing air cooling to obtain the coating, the porosity of the coating is below 1%, and the microhardness is 1000-1400 HV 0.2 . The relative erosion resistance is 6-8 times that of the base body. The application improves the microstructure, the bonding strength, the hardness and the erosion and wear resistance of the rare earth modified WC-10Ni coating, and has important significance for the development of the laser remelting technology.

Description

Technical Field

[0001] This invention relates to the field of tungsten carbide alloy modification, specifically to a laser remelting rare earth modified WC-10Ni coating and its preparation method. Background Technology

[0002] The turbine runner blades are crucial flow-through components in hydroelectric power generation. Due to their harsh operating environment, they are subjected to long-term erosion and wear from river sand and high-speed friction impacts in silty rivers, severely affecting the safe operation of the turbine and causing significant losses to the power plant's power generation efficiency. Therefore, the coating materials have extremely high performance requirements, ensuring high density, high hardness, and high erosion resistance.

[0003] 0Cr13Ni5Mo martensitic stainless steel is a high-quality super martensitic stainless steel. It is widely used in hydropower generation for components such as bearings, gears, valves, and turbine blades that bear static and dynamic loads and require corrosion resistance. However, in practical applications, it has been found that these components have low surface hardness and poor wear resistance, and are frequently subjected to erosion and wear from river sediment. Therefore, it is crucial to further improve the erosion and abrasion resistance of 0Cr13Ni5Mo martensitic stainless steel.

[0004] Surface thermal spraying technology has significant advantages in coating preparation. Currently, supersonic flame spraying is commonly used to modify the surface of 0Cr13Ni5Mo martensitic stainless steel to obtain wear-resistant coatings. However, coatings prepared by supersonic flame spraying have inherent structural defects, such as high porosity, which reduces the internal density and corrosion resistance of the coating; and residual stress, which leads to cracks in the coating and reduces the bonding strength between the coating and the substrate. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a laser remelting rare earth modified WC-10Ni coating and its preparation method, which can improve the density, hardness and erosion resistance of supersonic flame spraying coatings and solve the problem that the supersonic flame spraying preparation process cannot meet the high performance requirements of turbine flow components.

[0006] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a method for preparing a laser-remelted rare-earth modified WC-10Ni coating, characterized by comprising the following steps: Step 1: Pre-treat the 0Cr13Ni5Mo martensitic stainless steel matrix. Step 2: Prepare a rare earth modified WC-10Ni coating on the substrate surface using supersonic flame spraying technology. The powders used are WC-10Ni powder and CeO2 powder. The WC-10Ni powder has the following composition: Ni: 10wt%, WC: 90wt%, and CeO2 powder accounts for 0.5wt%-2wt% of the total powder mass. Step 3: Then, laser remelting is performed under inert gas protection, followed by air cooling to obtain the coating.

[0007] To further define it, the pretreatment involves grinding, cleaning, sandblasting, and preheating the substrate surface to 200°C.

[0008] Further specifying step 2, mechanical mixing is used, with a mixing time of 2 hours.

[0009] Further specifying the parameters for supersonic flame spraying are: powder feed rate 60 g / min, combustion chamber pressure 0.93 MPa, kerosene flow rate 5 L / min, oxygen flow rate 1650 L / min, spraying distance 300 mm, and layer thickness 400 μm.

[0010] Further specifying the parameters for laser remelting: laser power of 1500W, scanning speed of 400mm / min, distance of 300mm, and spot diameter of 20mm.

[0011] Furthermore, the laser scanning path adopts a spiral scanning method with an offset of 0.2mm.

[0012] Further specified, the inert gas is argon, and the gas flow rate is 15 L / min.

[0013] Furthermore, the cooling rate of air cooling is controlled at 15℃ / s.

[0014] Another object of the present invention is to provide a coating prepared by any of the above methods.

[0015] Further specified, the CeO2 content is 1%, the porosity of the coating is 0.41%, and the microhardness is 1400 HV. 0.2 The erosion weight loss was 3.8 mg.

[0016] Laser remelting can melt the supersonic flame sprayed coating to form a molten pool, filling the pores and cracks caused by spraying, making the coating denser and smoother, with better bonding strength, and achieving metallurgical bonding between the coating and the substrate.

[0017] Based on specific embodiments, the method of the present invention is as follows: WC-10Ni and CeO2 powders are weighed according to a preset ratio; the weighed powders are mechanically mixed in a container, and dried after uniform mixing; the surface of the 0Cr13Ni5Mo martensitic stainless steel substrate is ground, cleaned, sandblasted, and preheated; a rare earth modified WC-10Ni coating is prepared on the pretreated 0Cr13Ni5Mo martensitic stainless steel surface using supersonic flame spraying technology; after heat preservation and cooling to room temperature, the rare earth modified WC-10Ni supersonic flame sprayed coating is remelted by laser remelting to form a metallurgical bond. The resulting remelted layer is uniform and dense, with a porosity of less than 1% and a microhardness of 1000~1400 HV. 0.2 Its relative erosion resistance is 6 to 8 times that of the substrate.

[0018] Compared with the prior art, the present invention has the following beneficial effects: A rare-earth modified WC-10Ni coating was prepared on the surface of 0Cr13Ni5Mo martensitic stainless steel using a combined supersonic spraying and laser remelting process. Under given process conditions, the prepared coating exhibited excellent performance and formed a metallurgical bond with the substrate; the porosity was below 1%; and the microhardness ranged from 1000 to 1400 HV. 0.2 The relative erosion resistance is 6 to 8 times that of the substrate. This invention improves the bonding strength, hardness and erosion wear resistance of rare earth modified WC-10Ni coating, and is of great significance to the development of laser remelting technology.

[0019] After supersonic flame spraying, a coating with a CeO2 content of 1% was obtained, exhibiting a porosity of 1.95% and a microhardness of 1300 HV. 0.2 The erosion weight loss was approximately 6.5 times higher than that of the substrate; the erosion weight loss was 6.3 mg, approximately 5 times higher than that of the substrate. The method of this invention yields a laser-remelted rare-earth modified WC-10Ni coating with a CeO2 content of 1% and a porosity of 0.41%, which is approximately three times higher than that of a WC-10Ni supersonic flame-sprayed coating with a CeO2 content of 1%. The microhardness is 1400 HV. 0.2 The erosion weight loss is approximately 7 times higher than that of the substrate; the erosion weight loss is 3.8 mg, approximately 8 times higher than that of the substrate. Therefore, it can be used as the optimal formulation for the surface of 0Cr13Ni5Mo martensitic stainless steel.

[0020] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0021] Figure 1 XRD diffraction patterns of WC-10Ni laser remelted coatings with different CeO2 contents; Figure 2 shows the surface microstructure of WC-10Ni laser remelted layers at 200× and 2000× with different CeO2 contents. In the figure, (a1)(a2) CeO2 content is 0%, (b1)(b2) CeO2 content is 0.5%, (c1)(c2) CeO2 content is 1%, (d1)(d2) CeO2 content is 1.5%, and (e1)(e2) CeO2 content is 2%. Figure 3 The surface energy spectrum of a WC-10Ni broadband laser remelting layer with 1% CeO2 content is shown in the figure. (a) Surface scan region; (b) Elemental energy spectrum analysis; (c) W element; (d) Ni element; (e) O element; (f) C element; (g) Ce element. Figure 4 shows the cross-sectional microstructure of a WC-10Ni laser remelted layer with 0% CeO2 content. In the figure, (a) the remelted layer is magnified by 200×, (b) the remelted layer is magnified by 500×, and (c) the remelted layer is magnified by 1000×. Figure 5 The microstructure of a WC-10Ni laser remelted layer with a CeO2 content of 0.5% is shown in the figure. (a) Remelted layer magnification of 200×, (b) Remelted layer magnification of 500×, (c) Remelted layer magnification of 1000×. Figure 6 The microstructure of a WC-10Ni laser remelted layer with 1% CeO2 content is shown in the figure. (a) The remelted layer is magnified by 200×, (b) The remelted layer is magnified by 500×, and (c) The remelted layer is magnified by 1000×. Figure 7 The microstructure of a WC-10Ni laser remelted layer with a CeO2 content of 1.5% is shown in the figure. (a) The remelted layer is magnified by 200×, (b) The remelted layer is magnified by 500×, and (c) The remelted layer is magnified by 1000×. Figure 8 The microstructure of a WC-10Ni laser remelted layer with 2% CeO2 content is shown in the figure. (a) The remelted layer is magnified by 200×, (b) The remelted layer is magnified by 500×, and (c) The remelted layer is magnified by 1000×. Figure 9 shows the cross-sectional microstructure and porosity distribution of WC-10Ni broadband laser remelting layers with different CeO2 contents. In the figure, (a) CeO2 content is 0%, (b) CeO2 content is 0.5%, (c) CeO2 content is 1%, (d) CeO2 content is 1.5%, and (e) CeO2 content is 2%. Figure 10 Microhardness of WC-10Ni laser remelted layers with different CeO2 contents.

[0022] Figure 11 shows the erosion wear morphology of WC-10Ni laser remelting layers with different CeO2 contents. Detailed Implementation

[0023] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0024] Example 1: The method for preparing the laser remelting rare earth modified WC-10Ni coating in this embodiment is carried out according to the following steps: (1) Matrix pretreatment: The matrix is ​​0Cr13Ni5Mo martensitic stainless steel, and its main components are shown in Table 1 below. The 0Cr13Ni5Mo martensitic stainless steel plate was pretreated by sanding with sandpaper to remove impurities, then the sample surface was wiped with anhydrous ethanol, and finally the sample was allowed to air dry naturally before sandblasting. The sandblasting process parameters were: pressure 0.5 MPa, distance 180 mm, particle size 80#, spray angle 70°, and sandblasting time 8 s. After sandblasting, the substrate was preheated to 200°C using a flame heating method.

[0025] Table 1. Composition of the base 0Cr13Ni5Mo martensitic stainless steel (wt%)

[0026] (2) Supersonic flame spraying of rare earth modified WC-10Ni coating: WC-10Ni powder and CeO2 powder were mixed evenly at mass ratios of 100:0, 99.5:0.5, 99:1, 98.5:1.5, and 98:2, respectively, and then mechanically mixed for 2 hours. WC-10Ni powder consists of the following components: Ni: 10wt%, WC: 90wt%, and CeO2 powder accounting for 0.5wt%, 1wt%, 1.5wt%, and 2wt% of the total powder mass.

[0027] Using ball-milled powder, a rare earth modified WC-10Ni coating was prepared by spraying a 0Cr13Ni5Mo martensitic stainless steel substrate with a supersonic flame spraying device. The coating was then tested. The parameters of the supersonic flame spraying were: powder feed rate 60 g / min, combustion chamber pressure 0.93 MPa, kerosene flow rate 5 L / min, oxygen flow rate 1650 L / min, and spraying distance 300 mm. (3) Laser remelting treatment: The rare earth modified WC-10Ni coating prepared in step (2) was remelted using a laser remelting device. The laser power was 1500W, the scanning speed was 400mm / min, the distance was 300mm, the spot diameter was 20mm, and the protective gas nozzle was: central protective gas + annular protective gas. The laser scanning path adopted a spiral scanning method with an offset of 0.2mm. (4) Post-processing: The coating after ultra-high speed laser remelting is air-cooled at a rate of 15℃ / s.

[0028] In the process of preparing the coating, in order to obtain a high-quality and high-performance rare earth modified WC-10Ni coating, it is necessary to determine the optimal ratio of WC-10Ni powder to CeO2 powder. The influence of the coating powder ratio on the microstructure and properties of the rare earth modified WC-10Ni coating was studied, and the optimal ratio of WC-10Ni powder to CeO2 powder was determined. 1. Coating microstructure analysis and performance testing methods 1.1 Coating microstructure analysis (1) X-ray phase analysis of coating The laser remelted sample was wire-cut into 10mm × 10mm × 3mm pieces. Since oil residue remained on the cut surface after wire cutting, the oil was first removed with alcohol. Then, the coating surface of the sample was successively polished to a mirror finish using 400#, 600#, 800#, 1000#, 1200#, 1500#, and 2000# sandpaper. Finally, it was polished using a polishing machine with a 20% (w / w) diamond aqueous solution as the polishing fluid. X-ray diffraction was used to analyze the phase composition of the sample. The X-ray source was a Cu target, wavelength 1.54nm, tube voltage 30kV, current 30mA, scanning speed 6° / min, and the diffraction angle range was 20–90°. (2) Sample preparation and tissue morphology observation The laser remelted sample was wire-cut into 10mm×10mm×10mm pieces, and the edges of the sample were chamfered. Then, the cross-section of the test sample was polished with 400#, 600#, 800#, 1000#, 1200#, 1500#, and 2000# sandpaper in sequence, alternating vertically during polishing to ensure that the old scratches were completely removed. To prevent the abrasive shavings from causing secondary scratches on the sample cross-section, the polished surface was rinsed with running water to make the polished cross-section relatively flat. When the surface was polished to near mirror finish, it was polished on a polishing machine with a 20% diamond aqueous solution as the polishing fluid. The sample cross-section was polished to mirror finish, the cross-section was wiped with alcohol, and then quickly dried with a hair dryer.

[0029] (3) Calculation of coating porosity Metallographic images were taken using a Leica DMi8A metallographic microscope. The porosity of the sprayed and remelted coatings was analyzed using ImageJ software with a grayscale method. After polishing the sample cross-section to a mirror surface, 8-10 metallographic images were taken continuously along the same direction. The images were then imported into ImageJ software to obtain grayscale images, and the coating porosity was measured.

[0030] 1.2 Coating performance test (1) Microhardness test The specimens used for microhardness testing are the same specimens used for microscopic observation. An HV-1000A microhardness tester was used to test the microhardness of the specimens, with a loading force of 1.96 N and a loading time of 10 s. The microhardness of the rare-earth modified WC-10Ni coating was measured along the cross-section of the specimen. Ten points were measured perpendicular to the substrate from the coating surface, with a 50 μm interval between each point. Each point was measured at least three times in the transverse direction. Finally, the hardness data from each location were compiled, and the average microhardness was taken.

[0031] (2) Erosion wear test The MCF-40 corrosion erosion and wear testing machine was used to conduct erosion tests on sprayed and remelted coatings. Before the erosion test, the sample surface needed to be polished, cleaned to remove oil and dirt, and dried with cold air. The sample was then firmly fixed in the fixing hole on the rotating shaft of the erosion machine. The abrasive used for erosion was silica sand (SiO2) with a particle size range of 0.5-1 mm and a slurry concentration of 40%. During the erosion process, the rotational speed of the testing machine shaft was 815 r / min, the linear velocity of the turntable was 12.8 m / s, and the erosion time was 120 min. Each experiment was repeated three times to ensure the reliability of the experimental data.

[0032] 2. Determination of the optimal ratio of rare earth oxide CeO2 2.1 The WC-10Ni laser-remelted coatings with different CeO2 contents prepared by laser remelting on the surface of 0Cr13Ni5Mo martensitic stainless steel in Example 1 were subjected to microstructure and performance tests. Specifically, the phase composition, microstructure, microhardness and erosion resistance of the coatings were analyzed and tested using equipment such as X-ray diffractometer, scanning electron microscope, microhardness tester and erosion wear tester, and the optimal CeO2 content was selected.

[0033] (1) X-ray phase analysis of WC-10Ni laser remelting coatings with different CeO2 contents Figure 1XRD diffraction patterns of WC-10Ni laser-remelted coatings with different CeO2 contents are shown. The figures reveal that the elemental composition of the WC-10Ni laser-remelted coatings with different CeO2 contents is nearly identical, indicating that the CeO2 content does not significantly affect the diffraction peak intensity of the coating, nor does it cause the coating compounds to decompose due to high temperatures, thus maintaining phase stability.

[0034] (2) Surface microstructure of WC-10Ni laser remelting coatings with different CeO2 contents Figure 2 shows the surface microstructure of WC-10Ni laser-remelted coatings with different CeO2 contents at 200× and 2000×. In the figure, (a1)(a2) CeO2 content is 0%; (b1)(b2) CeO2 content is 0.5%; (c1)(c2) CeO2 content is 1%; (d1)(d2) CeO2 content is 1.5%; and (e1)(e2) CeO2 content is 2%. From the surface morphology of the laser-remelted layers in the figure, it can be seen that recrystallization occurred on the surface of the WC-10Ni laser-remelted coatings with different CeO2 contents. The typical lamellar structure and microparticle accumulation structure are reduced, and the roughness and density are significantly improved. This is because the unmelted particles in the supersonic flame sprayed coating are melted by the high temperature of the laser, filling the pores and cracks generated by the spraying, making the coating smooth and increasing its density. However, some pores still remain on the surface of the coating after laser remelting. This is because the laser melts the coating, filling the pores below the coating. Gas is expelled upwards from below the coating, and when the gas is expelled from the surface of the coating, it causes the surface coating density to decrease. When cooled, the particles shrink, resulting in pores on the surface of the coating. When the CeO2 content is 0%, the surface roughness of the coating is slightly improved, but there are still large particles, pores, and pits. When the CeO2 content is 0.5%, the surface roughness of the coating becomes smoother, the particles are refined due to the presence of CeO2, and the pores also become smaller. When the CeO2 content is 1%, the surface roughness of the coating becomes even smoother, and the particles are further refined. When the CeO2 content is 1.5%, the surface roughness of the coating worsens, and the particles gradually increase in size. This is because the increased CeO2 content causes some particles to agglomerate excessively, and the pores also become larger. When the CeO2 content is 2%, the surface roughness of the coating is even worse, and the particles further increase in size, indicating that excessive CeO2 will cause the surface roughness and internal structure of the coating to deteriorate.

[0035] Due to the increase of CeO2, the microstructure of the coating changed. When the CeO2 content was greater than 1%, the surface roughness of the coating began to deteriorate and the porosity increased. Therefore, the coating with a CeO2 content of 1% was selected for energy dispersive spectroscopy analysis to further analyze the specific distribution of each element in the coating.

[0036] Figure 3The surface energy dispersive spectroscopy (EDS) of a WC-10Ni broadband laser remelted layer with a CeO2 content of 1 wt.% is shown in the figures. (a) Surface scan region; (b) Elemental energy dispersive spectroscopy analysis; (c) W element; (d) Ni element; (e) O element; (f) C element; (g) Ce element. As can be seen from the figures, the WC-10Ni laser remelted layer with 1% rare earth CeO2 is mainly composed of W, Ni, O, C, and Ce elements. The W element content is 71.61%, the Ni element content is 10.30%, the O element content is 6.96%, the C element content is 10.89%, and the Ce element content is 0.24%. The Ce element is relatively dispersed, which improves the density of the coating, and there is no significant element segregation within the coating, indicating a relatively uniform element distribution.

[0037] (3) Cross-sectional microstructure of WC-10Ni laser remelted coatings with different CeO2 contents Figure 4 shows the cross-sectional microstructure of the WC-10Ni laser-remelted layer with 0% CeO2 content. (a) Remelted layer magnification 200×; (b) Remelted layer magnification 500×; (c) Remelted layer magnification 1000×. As can be seen from the figure, the WC-10Ni laser-remelted coating with 0% CeO2 content has a uniform and tight bond with the substrate, and the microcracks at the interface are significantly reduced, indicating that the bonding quality between the remelted layer and the substrate is significantly improved, and the coating and the substrate form a metallurgical bond. The porosity is significantly reduced and the microstructure is more compact. This is because the high temperature of the laser causes the coating to melt locally, and the molten material flows to fill the original pores. At the same time, the mechanical bond between WC particles and Ni-based bonding phase is transformed into a stronger metallurgical bond. The interface is blurred and the bonding strength is greatly improved. The rapid heating and cooling of the laser also inhibits grain growth, causing both the Ni-based phase and the carbide phase to form finer grains, laying the structural foundation for performance improvement.

[0038] Figure 5 The microstructure of a WC-10Ni laser-remelted layer with a CeO2 content of 0.5% is shown in the images: (a) magnification of the remelted layer at 200×; (b) magnification of the remelted layer at 500×; and (c) magnification of the remelted layer at 1000×. The WC-10Ni laser-remelted layer with a CeO2 content of 0.5% exhibits a reliable metallurgical bond with the substrate, with a clear transition zone at the interface. This is because during laser remelting, metal atoms diffuse into each other, undergoing a chemical reaction that transforms the bond from mechanical adhesion to metallic bonding. After high-temperature melting, the coating fuses with the substrate, resulting in better metallurgical bonding. Porosity is further reduced, and the microstructure exhibits stronger adhesion.

[0039] Figure 6The microstructure of a WC-10Ni laser-remelted layer with 1% CeO2 content is shown in the images: (a) magnification of the remelted layer at 200×; (b) magnification of the remelted layer at 500×; and (c) magnification of the remelted layer at 1000×. The WC-10Ni laser-remelted layer with 1% CeO2 content exhibits a reliable metallurgical bond with the substrate, and a clear transition zone exists at the interface. The coating has very few internal pores, no cracks, and a refined grain structure, further enhancing its performance.

[0040] Figure 7 The microstructure of a WC-10Ni laser-remelted layer with a CeO2 content of 1.5% is shown in (a) magnification of 200×, (b) magnification of 500×, and (c) magnification of 1000×. The WC-10Ni laser-remelted layer with a CeO2 content of 1.5% exhibits a reliable metallurgical bond with the substrate, with a clear transition zone at the interface. The coating shows a slight increase in porosity and a slight increase in grain size, but no internal cracks are observed, resulting in a slight decrease in microstructural properties.

[0041] Figure 8 The microstructure of a WC-10Ni laser-remelted layer with 2% CeO2 content is shown in the images. (a) Magnification of the remelted layer: 200×; (b) Magnification of the remelted layer: 500×; (c) Magnification of the remelted layer: 1000×. The WC-10Ni laser-remelted layer with 2% CeO2 content exhibits a reliable metallurgical bond with the substrate, and a clear transition zone exists at the interface. Excessive CeO2 increases the porosity of the coating and causes microcracks. This is because CeO2 has a high melting point. If too much is added, CeO2 cannot melt completely, resulting in a reduction in the number of effective crystal nuclei in the coating, and the grains become coarse and cannot be evenly distributed. CeO2 is a surface-active substance with a high affinity for elements such as O and N in the air. Therefore, if too much CeO2 is added, too much air will be mixed in the molten spray material. During the coating deposition process, the air cannot be expelled in time, reducing the deposition rate of the coating, resulting in a large number of pores and defects. The thickness of the layers formed in a single spraying pass is uneven, and fractures occur, leading to a decline in the microstructure properties.

[0042] (4) Porosity of WC-10Ni laser remelted coatings with different CeO2 contents Figure 9 shows the cross-sectional microstructure and porosity distribution of WC-10Ni broadband laser remelted layers with different CeO2 contents: (a) 0% CeO2 content; (b) 0.5% CeO2 content; (c) 1% CeO2 content; (d) 1.5% CeO2 content; and (e) 2% CeO2 content. The figure shows the 2000× cross-sectional morphology and porosity distribution of the WC-10Ni laser remelted layers with different CeO2 contents. Using ImageJ software, the porosity of the WC-10Ni broadband laser remelted layer with 2% CeO2 content was calculated to be 0.98%, which is the highest compared to other CeO2 contents. The WC-10Ni broadband laser remelted layer with 1% CeO2 content had the least porosity, with only 0.41%. The WC-10Ni broadband laser remelted layers with other CeO2 contents also reduced the porosity to varying degrees. The porosities of the WC-10Ni broadband laser remelted layers with CeO2 contents of 0%, 0.5%, and 1.5% were 0.68%, 0.59%, and 0.76%, respectively.

[0043] (5) Microhardness of WC-10Ni laser remelted coatings with different CeO2 contents Figure 10 Microhardness distribution diagrams of WC-10Ni laser-remelted layers with different CeO2 contents are shown from the surface of the remelted layer to the substrate. The hardness distribution trend shows that the hardness of the WC-10Ni laser-remelted layer first increases and then decreases, indicating that the remelted layer near the surface has higher porosity and poorer density, resulting in lower hardness; the intermediate coating has fewer pores, better density, and higher interfacial bonding strength. When the CeO2 content is 0%, the coating hardness is the highest, ranging from 1200 to 1600 HV. 0.2 The hardness fluctuates between these values, representing an increase of approximately 7 times compared to the substrate. With increasing CeO2 content, the hardness of the remelted layer first increases and then decreases. The highest hardness is observed in remelted layers containing CeO2 at a CeO2 content of 1%, while the lowest hardness is observed at a CeO2 content of 2%, with a hardness distribution ranging from 1000 to 1200 HV. 0.2 The reason for this is that excessive CeO2 causes agglomeration in the remelted layer, generating hard and brittle impurities, which damages the coating structure, increases the number of pores and cracks in the coating, and leads to a decrease in hardness.

[0044] (6) Erosion wear of WC-10Ni laser remelted coatings with different CeO2 contents Figure 11 shows the erosion wear morphology of WC-10Ni laser remelted layers with different CeO2 contents. During the erosion process, the hard particles on the coating surface are detached due to impact fatigue caused by the scouring and wear of solid particles, resulting in obvious scratches and furrows on the surface of the remelted layer. This indicates that the remelted layer is mainly subjected to cutting forces during the erosion process. Under the erosion wear condition, plastic deformation occurs, leading to micro-fatigue spalling. The main erosion wear mechanism is micro-cutting and micro-furrowing mechanism. The tangential component velocity of the abrasive particles produces plowing and cutting effects to varying degrees. As shown in the figure, with increasing erosion time, the eroded coating surface exhibits both spalling pits and fine, long, furrowed deformation ridges. This indicates that the Ni binder phase in the WC-10Ni laser remelted coating supports the hard WC particles. During the erosion wear test, these binder phases are eroded away first, forming small grooves. The appearance of these grooves in the Ni binder phase makes the material more susceptible to erosion by abrasive particles. Then, the hard WC particles protrude and are pulled out and peeled off, or the WC particles break apart. Table 2 shows that the weight loss of the WC-10Ni laser remelted layer with different CeO2 contents is much smaller than that of the substrate. When the CeO2 content is 1%, the WC-10Ni laser remelted layer has the smallest weight loss and its relative erosion resistance is 6-8 times that of the substrate (the average weight loss of the substrate during wear is 27.2 mg). This is because the coating bonding strength is enhanced after laser remelting, the internal structure is well bonded, and the porosity is reduced. When erosion particles exert micro-cutting action on the coating, they can only cause fatigue spalling of the hard phase particles on the coating surface that are not well bonded.

[0045]

[0046] Table 2. Erosion and wear loss of WC-10Ni laser remelted layers with different CeO2 contents. Analysis shows that when the CeO2 content is 1%, the WC-10Ni laser remelted layer has the fewest pores and cracks, high structural bonding strength, the highest microhardness among all WC-10Ni laser remelted layers with added CeO2, and excellent erosion resistance. Therefore, a CeO2 content of 1% is selected as the optimal ratio for the WC-10Ni laser remelted layer.

[0047] in conclusion: 1. The surface morphology of WC-10Ni laser-remelted layers with different CeO2 contents shows that the WC-10Ni laser-remelted layer with 0% CeO2 content has reduced porosity and cracks, resulting in a smoother coating and increased density. The WC-10Ni laser-remelted layers with CeO2 contents of 0.5% and 1% exhibit further reduced porosity and stronger bonding, with the WC-10Ni laser-remelted layer with 1% CeO2 content showing the best performance. The WC-10Ni laser-remelted layers with CeO2 contents of 1.5% and 2% show a clear boundary with the substrate; excessive CeO2 increases the internal porosity of the coating and causes fine cracks. From a phase composition perspective, there is no significant difference in the phase composition of the laser-remelted layers, but the WC-10Ni laser-remelted layer with 1% CeO2 content shows a more uniform elemental distribution.

[0048] 2. From the cross-sectional morphology of WC-10Ni laser remelted layers with different CeO2 contents, it can be seen that the WC-10Ni coating with 0% CeO2 content has significantly reduced porosity and a tighter microstructure; the WC-10Ni laser remelted layers with CeO2 contents of 0.5% and 1% have further reduced porosity and stronger microstructure bonding, with the WC-10Ni laser remelted layer with 1% CeO2 content showing the best performance; the WC-10Ni laser remelted layers with CeO2 contents of 1.5% and 2% have increased porosity and micro-cracks in the coating. Porosity analysis shows that the cross-sectional porosity of the WC-10Ni laser remelted layer with 0% CeO2 content is 0.68%; the cross-sectional porosity of the WC-10Ni supersonic flame sprayed laser remelted layer with 0.5% CeO2 content is 0.59%; the cross-sectional porosity of the WC-10Ni laser remelted layer with 1% CeO2 content is the lowest, at only 0.41%; the cross-sectional porosity of the WC-10Ni laser remelted layer with 1.5% CeO2 content is 0.76%; and the cross-sectional porosity of the WC-10Ni laser remelted layer with 2% CeO2 content is the highest, at 0.98%.

[0049] 3. Microhardness analysis of WC-10Ni laser remelted layers with different CeO2 contents shows that the coating hardness is highest when the CeO2 content is 0%, reaching 1200 HV. 0.2 -1600HV 0.2 Compared to the substrate, the hardness increased by about 7 times. With increasing CeO2 content, the coating hardness first increased and then decreased. Among broadband laser remelted layers containing CeO2, the remelted layer with a CeO2 content of 1% had the highest hardness, while the coating hardness was lowest when the CeO2 content was 2%.

[0050] 4. Erosion and wear analysis of WC-10Ni laser remelted layers with different CeO2 contents shows that when the CeO2 content is 0%, the weight loss of the WC-10Ni laser remelted layer is 4.3 mg; when the CeO2 content is 0.5%, the weight loss is 4.7 mg; when the CeO2 content is 1%, the weight loss is the smallest, at 3.8 mg; when the CeO2 content is 1.5%, the weight loss is the largest, at 4.9 mg; and when the CeO2 content is 2%, the weight loss is 4.8 mg.

[0051] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the technical solutions of the present invention.

Claims

1. A method for preparing a laser-remelted rare-earth modified WC-10Ni coating, characterized in that, Includes the following steps: Step 1: Pre-treat the 0Cr13Ni5Mo martensitic stainless steel matrix. Step 2: Prepare a rare earth modified WC-10Ni coating on the substrate surface using supersonic flame spraying technology. The powders used are WC-10Ni powder and CeO2 powder. The WC-10Ni powder has the following composition: Ni: 10wt%, WC: 90wt%, and CeO2 powder accounts for 0.5wt%-2wt% of the total powder mass. Step 3: Then, laser remelting is performed under inert gas protection, followed by air cooling to obtain the coating.

2. The method according to claim 1, characterized in that, Pretreatment involves grinding, cleaning, sandblasting, and preheating the substrate surface.

3. The method according to claim 1, characterized in that, Step 2: Mechanical mixing of powders.

4. The method according to claim 1, characterized in that, The parameters for supersonic flame spraying are: powder feed rate 60 g / min, combustion chamber pressure 0.93 MPa, kerosene flow rate 5 L / min, oxygen flow rate 1650 L / min, spraying distance 300 mm, and layer thickness 400 μm.

5. The method according to claim 1, characterized in that, The parameters for laser remelting are: laser power of 1500W, scanning speed of 400mm / min, distance of 300mm, and spot diameter of 20mm.

6. The method according to claim 1, characterized in that, The laser scanning path adopts a spiral scanning method with an offset of 0.2mm.

7. The method according to claim 1, characterized in that, The inert gas is argon, and the gas flow rate is 15 L / min.

8. The method according to claim 1, characterized in that, The cooling rate of air cooling is controlled at 15℃ / s.

9. A coating prepared by the method of claims 1-7.

10. The coating according to claim 8, characterized in that, The CeO2 content is 1 wt%, the porosity of the coating is 0.41%, and the microhardness is 1400 HV. 0.2 The erosion weight loss was 3.8 mg.

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