A method for improving surface quality and performance of laser cladding NiCrSiBC-WC composite coating

Abstract

The application discloses a method for improving the surface quality and performance of a laser cladding NiCrSiBC-WC composite coating, relates to the field of composite coating surface processing technology, and aims at solving the problem that the coating prepared through single laser cladding is prone to cracks. The method comprises the following steps: S1, pretreatment of a base material; S2, preparation of laser cladding powder; S3, laser cladding treatment; S4, temperature field auxiliary treatment; and S5, laser remelting composite temperature field auxiliary treatment. The laser remelting composite temperature field auxiliary technology can break the limitation of the WC material addition amount on the performance of the coating, and a low-WC-mass-fraction high-hardness crack-free NiCrSiBC-WC composite coating can be obtained through the technology. The structure compactness of the NiCrSiBC-WC coating is improved, and the surface hardness and bonding force of the coating are improved.

Description

Technical Field

[0001] This invention relates to the field of composite coating surface processing technology, specifically a method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings. Background Technology

[0002] Laser cladding technology allows for precise control of laser energy and speed, achieving uniformity and stability in coatings. Furthermore, the rapid solidification rate during laser cladding promotes the formation of fine grains and a uniform microstructure, improving coating performance and stability. NiCrSiBC alloys possess high melting points and good thermal stability, maintaining good mechanical and chemical properties even at high temperatures. Composite coatings combining NiCrSiBC alloys with WC particles not only increase coating hardness but also enhance corrosion resistance. Moreover, the addition of WC particles further improves the coating's high-temperature resistance, making it suitable for high-temperature operating environments. Currently, laser-clad NiCrSiBC-WC composite coatings are widely used in various application fields. Existing research has found that the hardness and wear resistance of NiCrSiBC-WC composite coatings are highly dependent on the WC mass fraction. However, high WC mass fractions in NiCrSiBC-WC composite coatings can lead to cracking and increased manufacturing costs, while low WC mass fractions can reduce hardness.

[0003] The main reasons for cracks in coatings prepared by laser cladding alone are: firstly, the uneven distribution of WC particles and precipitated carbides in the Ni-based binder metal leads to interfacial stress between the Ni-based binder metal and the carbides; secondly, the high temperature gradient during laser cladding causes thermal stress in the coating; and finally, the thermal damage caused by the thermal decomposition of WC particles in the cladding layer, combined with these factors, results in cracking behavior in the cladding layer.

[0004] Meanwhile, laser cladding of NiCrSiBC-WC composite coatings still faces some technical bottlenecks, such as crack suppression, poor surface quality, low hardness, unstable adhesion between the coating and the substrate, and limited wear and corrosion resistance. Therefore, developing a new method to improve the surface quality and performance of NiCrSiBC-WC composite coatings to overcome these shortcomings of existing technologies is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings, which solves the problem of easy cracking in coatings prepared by laser cladding alone. By eliminating microcracks and incompletely melted particles in laser-clad NiCrSiBC-WC composite coatings, the overall hardness of the coating is improved.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for improving the surface quality and performance of laser cladding NiCrSiBC-WC composite coatings, comprising the following steps:

[0007] S1. Pretreatment of matrix material

[0008] Remove oil and rust from the surface of the alloy substrate;

[0009] S2, Preparation of laser cladding powder

[0010] Preparation of laser cladding alloy powder;

[0011] S3, Laser Cladding Process

[0012] Laser cladding of alloy powder on the surface of an alloy matrix;

[0013] S4, Temperature Field Auxiliary Processing

[0014] The alloy substrate with NiCrSiBC-WC composite coating prepared in step S3 is placed on a temperature field auxiliary device, and the heating temperature is set to 450℃ and maintained.

[0015] S5, Laser Remelting Composite Temperature Field Auxiliary Processing

[0016] When the temperature of the alloy matrix rises to 450°C, laser remelting is performed on the alloy matrix based on step S4.

[0017] Further, in step S1, 50# to 400# sandpaper is selected to polish the alloy substrate to remove oil and rust from the surface of the alloy substrate. The polished alloy substrate is rinsed with deionized water, ultrasonically cleaned with acetone or anhydrous ethanol for 3 to 5 minutes, rinsed with deionized water again, and then air-dried.

[0018] Furthermore, in step S2, a small amount of boron and silicon are added to the alloy powder.

[0019] Furthermore, in step S3, a robotic arm is used to control the scanning path of the laser.

[0020] Furthermore, in step S3, the scanning path is a single-layer path and a round-trip progressive path.

[0021] Furthermore, in step S3, the process parameters for laser cladding are as follows: laser power is 1000W, spot diameter is 2.5mm, scanning speed is 1200mm / min, overlap rate is 40%, and powder feeding rate is 11.2g / min.

[0022] Furthermore, in step S3, to prevent oxidation of the molten pool, argon gas with a flow rate of 5 L / min is introduced through a nozzle with a diameter of 10 mm as a protective gas. The purity of the protective gas is 99.9%, and the protective gas nozzle is tilted at a 45° angle to the molten pool.

[0023] Furthermore, in step S4, the temperature field auxiliary device uses a small heating furnace to heat the alloy substrate. The alloy substrate is placed on the heating resistance wire of the temperature field auxiliary device, and the heating temperature is adjusted by a temperature control switch. At the same time, a temperature measuring instrument is used to monitor the temperature of the alloy substrate in real time.

[0024] Furthermore, in step S5, during laser remelting assisted by the composite temperature field, the laser power is adjusted to 900W, the scanning speed is adjusted to 1000mm / min, the powder feeding channel is closed, and the laser beam is adjusted from the direction perpendicular to the alloy substrate to the direction tilted at 45°.

[0025] The beneficial effects of this invention are as follows: The laser remelting combined with temperature field-assisted technology of this invention overcomes the limitation of WC material addition on coating performance. This technology can obtain high-hardness, crack-free NiCrSiBC-WC composite coatings with low WC mass fraction, saving manufacturing costs and improving economic efficiency. The laser remelting technology combined with temperature field-assisted technology of this invention improves the structural density of the NiCrSiBC-WC coating, thereby enhancing the coating's surface hardness and adhesion, as well as its high-temperature oxidation resistance, corrosion resistance, and wear resistance. The laser remelting equipment and temperature field-assisted equipment of this invention are simple to operate, highly stable, and highly efficient, facilitating industrial production. Attached Figure Description

[0026] Figure 1 This is a diagram of the laser scanning path;

[0027] Figure 2 This is a top view of the temperature field auxiliary device;

[0028] Figure 3 Comparison of macroscopic surface morphology between original laser cladding samples with 30% WC and 40% WC and laser remelting samples processed under combined temperature field assistance.

[0029] Figure 4 Microstructure images of coating surfaces prepared for laser remelting and temperature field-assisted composite processes of 30% WC and 40% WC;

[0030] Figure 5 Comparison of microhardness between the sample prepared for the laser remelting composite temperature field assisted process and the original laser cladding sample;

[0031] Figure 6 XRD diffraction patterns of 30%WC and 40%WC laser remelting and temperature field-assisted composite processes;

[0032] Figure 7 This is a composition diagram of laser cladding alloy powder;

[0033] Figure 8 Residual stress diagrams for 30% WC and 40% WC laser remelting and temperature field-assisted composite processes and the original laser cladding process;

[0034] In the figure: 1 Temperature field auxiliary equipment, 2 Resistance wire, 3 Alloy matrix. Detailed Implementation

[0035] The following describes in detail, with reference to the accompanying drawings, a method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to the present invention.

[0036] A method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings includes the following steps:

[0037] S1. Pretreatment of matrix material

[0038] Use 50# to 400# sandpaper to polish the alloy substrate to remove oil and rust from the surface. Rinse the polished alloy substrate with deionized water, then ultrasonically clean it with acetone or anhydrous ethanol for 3 to 5 minutes. Rinse it with deionized water again and let it air dry.

[0039] S2, Preparation of laser cladding powder

[0040] according to Figure 7 Prepare laser cladding alloy powder according to the indicated proportions. Adding a small amount of boron to the alloy powder can lower the melting point of the matrix, and adding a small amount of silicon can increase the self-fluxing property of the alloy.

[0041] S3, Laser Cladding Process

[0042] Laser cladding of alloy powder was performed on a robotic laser cladding workstation (LYRF-4000W) equipped with a high-end cladding integrated control system (LYRF1500). A robotic arm controlled the laser scanning path, and a high-energy laser beam was emitted from the laser cladding emitter as the energy source. Due to the high stability of the laser cladding process, this invention employs a coaxial powder feeding method, simultaneously feeding powder while emitting the laser beam. The molten alloy powder gradually clads onto the alloy substrate as the laser heat source moves, forming multiple coating layers as the scanning path changes. Preliminary experiments selected the following process parameters for laser cladding: laser power 1000W, spot diameter 2.5mm, scanning speed 1200mm / min, overlap rate 40%, and powder feeding rate 11.2g / min. To prevent oxidation of the molten pool, argon gas with a flow rate of 5L / min was introduced through a 10mm diameter nozzle as a protective gas. The protective gas purity was 99.9%, and the nozzle was tilted at a 45° angle to the molten pool.

[0043] S4, Temperature Field Auxiliary Processing

[0044] The alloy substrate sample with the NiCrSiBC-WC composite coating prepared in step S3 was placed on the temperature field auxiliary device 1, and the heating temperature was set to 450℃ and maintained until the end of the test. The temperature field auxiliary device used a small heating furnace to heat the alloy substrate. The alloy substrate 3 was placed on the heating resistance wire 2, and the heating temperature was adjusted by a temperature control switch. At the same time, a thermometer was used to monitor the temperature of the alloy substrate in real time.

[0045] S5, Laser Remelting Composite Temperature Field Auxiliary Processing

[0046] When the temperature of the alloy substrate sample rises to 450℃, laser remelting is continued on the alloy substrate sample based on step S4. When performing laser remelting with the assistance of a composite temperature field, the laser power needs to be adjusted to 900W and the scanning speed to 1000mm / min. The laser remelting process uses the same equipment as the separate laser cladding process, with the powder feeding channel closed and the laser beam adjusted from a direction perpendicular to the alloy substrate to a 45° angle. The laser cladding emitter ejects the laser beam and performs laser remelting on the NiCrSiBC-WC composite coating along the corresponding scanning path.

[0047] S6. Pretreatment of samples processed under laser remelting composite temperature field assisted processing

[0048] The alloy matrix sample obtained in step S5 was cut into 10mm×10mm×8mm test samples using an electrical discharge wire cutting machine. Then, it was polished with metallographic sandpaper of 50 mesh, 200 mesh, 400 mesh, 800 mesh and 1600 mesh. Then, it was polished on an automatic polishing machine with 0.2μm diamond polishing agent until no scratches were visible on the sample surface. Finally, the sample was placed in an acetone solution for ultrasonic cleaning to remove impurities.

[0049] The method of the present invention will be described in detail below with reference to specific embodiments. 45# steel with dimensions of 60mm × 40mm × 8mm is selected as the alloy matrix, and the process is carried out according to the following steps:

[0050] S1, Pretreatment of the matrix

[0051] Use 50# sandpaper to polish the alloy substrate, removing oil and rust from its surface. Rinse the polished substrate with deionized water, then ultrasonically clean it with acetone or anhydrous ethanol for 4 minutes. Rinse again with deionized water and allow it to air dry. The purpose of rinsing with deionized water is to remove dirt, the purpose of ultrasonic cleaning with acetone or anhydrous ethanol is to remove oil, and the purpose of rinsing with deionized water is to remove any remaining substances on the surface.

[0052] S2, Preparation of laser cladding powder

[0053] according to Figure 7 The alloy powder is prepared in the proportions shown. Adding a small amount of boron to the alloy powder can lower the melting point of the matrix, and adding a small amount of silicon can increase the self-fluxing property of the alloy.

[0054] S3, Laser Cladding Process

[0055] Laser cladding is performed on a robotic laser cladding workstation (LYRF-4000W) equipped with a high-end cladding integrated control system (LYRF1500). The laser cladding emitter emits a high-energy laser beam as the energy source, and a robotic arm controls the laser's scanning path. Figure 1 As shown, the scanning path is set as a single-layer path and a reciprocating progressive path. This invention employs a coaxial powder feeding method, simultaneously feeding powder while emitting the laser beam. The molten alloy powder gradually clads onto the alloy substrate as the laser heat source moves, forming multiple coating layers as the scanning path changes. The parameters for laser cladding are: laser power 1000W, spot diameter 2.5mm, scanning speed 1200mm / min, overlap rate 40%, and powder feeding rate 11.2g / min. To prevent oxidation of the molten pool, argon gas with a flow rate of 5L / min is introduced through a 10mm diameter nozzle as a protective gas. The protective gas purity is 99.9%, and the nozzle is tilted at a 45° angle to the molten pool.

[0056] S4, Temperature Field Auxiliary Processing

[0057] The alloy substrate sample with the NiCrSiBC-WC composite coating prepared in step S3 was placed on a temperature field auxiliary device, and the heating temperature was set to 450℃ and maintained until the end of the test. The temperature field auxiliary device used a small heating furnace to heat the alloy substrate. The alloy substrate was placed on the heating resistance wire, and the heating temperature was adjusted by a temperature control switch. The substrate temperature was monitored in real time by a thermometer during heating.

[0058] S5, Laser Remelting Composite Temperature Field Auxiliary Processing

[0059] When the sample temperature reaches 450℃, laser remelting is performed on the alloy substrate sample based on step S4. During laser remelting under the combined temperature field assisted treatment, the laser power is adjusted to 900W and the scanning speed to 1000mm / min. The laser remelting process uses the same equipment as the standalone laser cladding process, with the powder feeding channel closed and the laser beam adjusted from a direction perpendicular to the alloy substrate to an angle of 45°. The laser cladding emitter ejects the laser beam and performs laser remelting on the NiCrSiBC-WC composite coating along the corresponding scanning path.

[0060] S6. Pretreatment of samples processed under laser remelting composite temperature field assisted processing

[0061] The alloy matrix sample processed in step S5 was cut into 10mm×10mm×8mm test samples using an electrical discharge wire cutting machine. Then, it was polished with metallographic sandpaper of 50 mesh, 200 mesh, 400 mesh, 800 mesh and 1600 mesh. Then, it was polished with 0.2μm diamond polishing agent on an automatic polishing machine until no scratches were visible on the sample surface. Finally, the sample was placed in acetone solution for ultrasonic cleaning to remove impurities and obtain the test sample.

[0062] Metallographic specimens were prepared by etching the surface and cross-section of the test sample prepared in step S6 using aqua regia (HCl:HNO3 = 3:1 solution). The microstructure morphology of the specimens was then observed using a super depth-of-field microscope. Figure 4 As shown, the coarse WC dendrites undergo re-decomposition and growth. At higher temperatures and faster cooling rates, some WC columnar crystals gradually grow into WC equiaxed crystals, resulting in grain refinement. Figure 4 Figure b1 shows the microstructure of the 40% WC composite coating. It was observed that the WC particles were evenly distributed and there was no obvious aggregation, which is attributed to the promoting effect of the temperature field-assisted process.

[0063] The surface hardness and cross-sectional hardness changes of the coating were measured using a Vickers hardness tester (HXD-1000TMC), and the results are as follows: Figure 5As shown, after laser remelting, the surface hardness of the two ceramic coatings (30 wt.%WC and 40 wt.%WC) are 598.3 HV and 647.5 HV, respectively, which are much greater than the surface hardness values ​​(525.8 HV and 571.3 HV) of the laser cladding coatings alone (50 wt.%WC and 60 wt.%WC).

[0064] The residual stress of each sample was measured using X-ray diffraction sin²ψ (Proto iXRD-COMBO). Elastic strain at the WC(202) Bragg peak was determined using nickel-filtered copper source Cr-kα radiation at approximately 143° 2θ under conditions of 45 kV and 40 mA. Figure 8 As shown, the residual stresses of the two coatings (30 wt.%WC and 40 wt.%WC) were measured and analyzed to be 280.17 MPa and 313.23 MPa, respectively, which are much smaller than the residual stress values ​​of the laser cladding coatings alone (50 wt.%WC and 60 wt.%WC) (380.78 MPa and 419.71 MPa).

[0065] This invention proposes a method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings using a laser remelting composite temperature field. This method eliminates microcracks and incompletely melted particles (WC ceramic particles and Ni-based alloy particles) present in the laser-clad NiCrSiBC-WC composite coating, allowing WC particles to be well preserved while producing grain refinement. The fine carbide particles decomposed during the laser cladding and remelting process also improve the overall hardness of the coating.

[0066] 1. Eliminated microcracks and incompletely melted particles

[0067] like Figure 3 As shown, this invention remelts the original laser-clad NiCrSiBC-WC composite coating into a liquid molten pool. Unmelted WC ceramic particles and Ni-based alloy particles on the surface are melted into the liquid molten pool by the laser, thus dissolving completely into the coating. The troughs of the original laser-clad NiCrSiBC-WC composite coating are filled with molten metal, ultimately reducing the peak height difference. The coating after laser remelting with a composite temperature field assisted treatment is smoother and flatter, with a more uniform and denser macroscopic morphology.

[0068] II. Retaining WC particles and refining grain size

[0069] During the laser remelting composite temperature field-assisted processing, the laser inputs heat to the surface of the coating after temperature field assistance, making the temperature of the laser-remelted coating higher than that of the sample coating in step S3. This causes the coarse WC dendrites to re-decompose and grow. Under higher temperatures and faster cooling rates, some WC columnar crystals gradually grow into WC equiaxed crystals, resulting in grain refinement. Figure 4 Figure b1 shows the microstructure of the 40% WC composite coating. It was observed that the WC particles were evenly distributed and there was no obvious aggregation. This is due to the promoting effect of the temperature field-assisted process. Compared with the 30% WC composite coating, the dendritic structure of the 40% WC coating is further refined.

[0070] III. Suppressing cracking and increasing hardness

[0071] The main reasons for cracking in coatings prepared by traditional laser cladding are: firstly, the uneven distribution of WC particles and precipitated carbides in the Ni-based binder metal, leading to interfacial stress between the Ni-based binder metal and the carbides; secondly, the high temperature gradient during laser cladding causes thermal stress in the coating; and finally, thermal damage from the thermal decomposition of WC particles in the cladding layer. These combined effects result in cracking of the cladding layer. In contrast to laser cladding alone, a composite coating with higher hardness and less cracking can be obtained through a laser remelting combined with a temperature field-assisted process. On one hand, the temperature field assistance and laser remelting process effectively improve the uniform distribution of WC particles, helping to reduce interfacial stress in the coating; on the other hand, the temperature field assistance significantly reduces the temperature gradient and cooling rate between the coating and the substrate, reducing thermal stress. Laser remelting allows the coating surface to remelt, helping to release surface thermal stress; finally, the temperature field assistance reduces the thermal damage to WC particles during laser cladding and laser remelting. Therefore, the residual stress generated by the laser remelting combined with a temperature field-assisted process is less than that generated by laser cladding alone. Figure 5 As shown, a crack-free, high-hardness WC ceramic-metal composite coating was thus obtained.

[0072] like Figure 6 As shown, the coating treated by the laser remelting composite temperature field assisted process introduces a large laser energy to impact the molten pool at high temperature, promoting the partial dissolution of in-situ WC and W2C particles. The decomposition releases W and C free atoms, which react with solute atoms to generate complex carbides such as M7C3 and M6C in the composite coating. The number and types of carbides in the coating will further increase. These hard phase carbides distributed in the coating can play a role in solid solution strengthening and improve the surface hardness of the coating.

[0073] Compared with the prior art, the advantages of the present invention are as follows:

[0074] (1) Laser remelting composite temperature field assisted technology has gotten rid of the limitation of WC material addition on coating performance. This technology can be used to obtain high hardness and crack-free NiCrSiBC-WC composite coating with low WC mass fraction, saving manufacturing costs and improving economic efficiency.

[0075] (2) Laser remelting technology combined with temperature field-assisted technology improves the surface hardness and adhesion of NiCrSiBC-WC coating by improving the structural density of the coating, as well as its high-temperature oxidation resistance, corrosion resistance and wear resistance.

[0076] (3) Laser remelting equipment and temperature field auxiliary equipment are simple to operate, highly stable and efficient, which is conducive to industrial production.

Claims

1. A method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings, characterized in that, Includes the following steps: S1. Pretreatment of matrix material Remove oil and rust from the surface of the alloy substrate; S2, Preparation of laser cladding powder Preparation of laser cladding alloy powder; S3, Laser Cladding Process Laser cladding of alloy powder on the surface of an alloy matrix; S4, Temperature Field Auxiliary Processing The alloy substrate with NiCrSiBC-WC composite coating prepared in step S3 is placed on a temperature field auxiliary device, and the heating temperature is set to 450℃ and maintained. S5, Laser Remelting Composite Temperature Field Auxiliary Processing When the temperature of the alloy matrix rises to 450°C, laser remelting is performed on the alloy matrix based on step S4.

2. The method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to claim 1, characterized in that, In step S1, use 50# to 400# sandpaper to polish the alloy substrate to remove oil and rust from the surface. Rinse the polished alloy substrate with deionized water, then ultrasonically clean it with acetone or anhydrous ethanol for 3 to 5 minutes. Rinse it with deionized water again and let it air dry.

3. The method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to claim 2, characterized in that, In step S2, a small amount of boron and silicon are added to the alloy powder.

4. The method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to claim 3, characterized in that, In step S3, a robotic arm is used to control the scanning path of the laser.

5. The method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to claim 4, characterized in that, In step S3, the scanning path is a single-layer path and a round-trip progressive path.

6. The method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to claim 5, characterized in that, In step S3, the laser cladding process parameters are as follows: laser power is 1000W, spot diameter is 2.5mm, scanning speed is 1200mm / min, overlap rate is 40%, and powder feeding rate is 11.2g / min.

7. The method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to claim 6, characterized in that, In step S3, to prevent oxidation of the molten pool, argon gas with a flow rate of 5 L / min is introduced through a nozzle with a diameter of 10 mm as a protective gas. The purity of the protective gas is 99.9%, and the protective gas nozzle is tilted at a 45° angle to the molten pool.

8. The method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to claim 7, characterized in that, In step S4, the temperature field auxiliary device uses a small heating furnace to heat the alloy substrate. The alloy substrate is placed on the heating resistance wire of the temperature field auxiliary device, and the heating temperature is adjusted by a temperature control switch. At the same time, a temperature measuring instrument is used to monitor the temperature of the alloy substrate in real time.

9. A method for improving the surface quality and performance of laser-clad NiCrSiBC-WC composite coatings according to claim 8, characterized in that, In step S5, during laser remelting assisted by the composite temperature field, the laser power is adjusted to 900W, the scanning speed is adjusted to 1000mm / min, the powder feeding channel is closed, and the laser beam is adjusted from the direction perpendicular to the alloy substrate to the direction tilted at 45°.

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