A method for preparing a laser cladding composite coating

Abstract

The application provides a preparation method of a laser cladding composite coating, and the preparation method is as follows: the raw material of the composite coating comprises cubic boron nitride powder, the composite coating is prepared on a base material by using a laser cladding technology, and the cubic boron nitride powder generates phase transition under the action of laser to form the composite coating with cubic boron nitride and hexagonal boron nitride. The preparation method is adjusted to realize the conversion of cubic boron nitride (cBN) to hexagonal boron nitride (hBN) in the process of laser spraying, and the proportion of cBN and hBN is reasonably controlled, so that the cBN and hBN synergistically act to obtain the composite coating with the hardness and lubricating performance.

Description

Technical Field

[0001] This invention relates to the technical field of coating preparation, and specifically to a method for preparing a laser cladding composite coating. Background Technology

[0002] Laser cladding coatings possess characteristics such as dense structure, metallurgical bonding, high hardness, and high wear resistance. However, its application in specific working environments is limited due to its high dilution rate and low production efficiency. Ultra-high-speed laser cladding is a highly efficient surface technology developed from laser cladding. By rationally adjusting the light and powder, it achieves the most ideal interaction between light and powder in space, resulting in more stable powder melting and more efficient energy utilization. Its process characteristics endow ultra-high-speed laser cladding with many advantages, such as less heat input to the substrate, thereby reducing residual stress inside the coating and reducing coating defects. Therefore, surface strengthening of workpieces through ultra-high-speed laser cladding has become a research hotspot in the field of surface engineering for mechanical parts.

[0003] Metal-based coatings are widely used; however, with increasingly harsh working conditions, their performance is struggling to meet service requirements. Compared to metal-based materials, ceramic materials are far superior in terms of hardness, high-temperature strength, and wear resistance. Therefore, adding ceramic particles to metal coatings to prepare ceramic-reinforced metal-based composite coatings can significantly improve material properties.

[0004] While the addition of common ceramic materials can improve the hardness and wear resistance of the coating, its effect on reducing friction is not significant and may even lead to an increase in the coefficient of friction. Some studies have chosen to add solid lubricants such as graphene, MoS2, and WS2 to solve the above problems. However, due to the low melting point of these materials, they are easily burned off under the action of high-energy laser beams, making it difficult to retain them in the coating to play their role. At the same time, they may also generate some compounds that lead to a decrease in coating performance.

[0005] Cubic boron nitride (cBN), as a ceramic reinforcing phase, is a novel ceramic material. Its hardness is second only to diamond, classifying it as an ultrahard material. Due to its outstanding properties such as high strength, high hardness, good corrosion resistance, good wear resistance, good heat resistance, and high chemical resistance, it has become one of the most promising structural materials in engineering applications.

[0006] Therefore, existing technologies need further development. Summary of the Invention

[0007] To address the shortcomings of existing technologies and solve the aforementioned problems, a method for preparing laser cladding composite coatings is proposed, and the following technical solution is provided:

[0008] A method for preparing a laser cladding composite coating, wherein the raw material of the composite coating includes cubic boron nitride powder, and the composite coating is prepared on a substrate using laser cladding technology. The cubic boron nitride undergoes a phase transition under the action of a high-energy laser beam to form a composite coating that simultaneously contains cubic boron nitride and hexagonal boron nitride.

[0009] Furthermore, the ratio of cubic boron nitride to hexagonal boron nitride formed is 60%-70%: 30%-40%.

[0010] Furthermore, the raw materials for the composite coating also include chromium-nickel alloy powder. The chromium-nickel alloy powder is mixed with cubic boron nitride powder and then ground to form a mixed powder. The mixed powder is used as the raw material for the composite coating for laser cladding.

[0011] Furthermore, the amount of cubic boron nitride powder added is 15wt%-20wt% of the chromium-nickel alloy powder.

[0012] Furthermore, the process parameters for laser cladding are as follows: laser power is set to 1800W-2300W, scanning rate is 220-250mm / s, and overlap rate is 85%-90%.

[0013] Furthermore, during the laser spraying process, a physical field is set to assist the cubic boron nitride powder in undergoing a phase transition.

[0014] Furthermore, the physical field is provided by an ultrasonic device, the output power of which is 70%-80%.

[0015] Furthermore, the overlap rate of the composite coating is set to 85%-90%.

[0016] Furthermore, the substrate is a titanium alloy.

[0017] Beneficial effects:

[0018] 1. The laser cladding composite coating preparation method of the present invention realizes the conversion of cBN to hexagonal boron nitride (hBN) during the laser spraying process by adjusting the preparation method, and reasonably controls the ratio of cBN and hBN so that cBN and hBN work synergistically to obtain a composite coating that takes into account both hardness and lubrication performance.

[0019] 2. In this invention, titanium alloy is used as the substrate. During the laser cladding process, titanium combines with nitrogen in the decomposed cBN to generate TiN in the coating, thereby increasing the hardness of the coating.

[0020] 3. This invention explores the optimal content of cubic boron nitride and the best laser cladding parameters to achieve optimal coating performance. Attached Figure Description

[0021] Figure 1This is a schematic diagram of the laser cladding device of the present invention. (a) is a left view and (b) is a front view.

[0022] Figure 2 This is a schematic diagram of the overlap rate of the composite coating;

[0023] Figure 3 These are the transmission electron microscope (HRTEM) high-resolution images and their Fourier transform (FFT) images of Example 1, Comparative Example 1, and Comparative Example 2. (a) and (d) are the HRTEM and FFT images of Comparative Example 2, (b) and (e) are the HRTEM and FFT images of Example 1, and (c) and (f) are the HRTEM and FFT images of Comparative Example 1.

[0024] Figure 4 The graphs show the trends of hardness and friction coefficient of the composite coatings in Examples 1, 4, and 5, where A represents the hardness trend of the composite coatings in Examples 1-3, and B represents the friction coefficient trend of the composite coatings in Examples 1-3.

[0025] The above figures include the following reference numerals:

[0026] 1. Laser cladding device; 11. Powder feeder; 12. Laser beam; 13. Mixed powder; 21. Ultrasonic transducer; 22. Ultrasonic tool head; 23. Fixture; 24. High-speed reciprocating platform; 25. Ultrasonic wave; 3. Substrate; 4. Overlapping part. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application.

[0028] According to an embodiment of the present invention, a method for preparing a laser cladding composite coating is provided. The preparation method is as follows: the raw material of the composite coating includes cubic boron nitride powder. The raw material of the composite coating is sprayed onto a substrate using a laser cladding method. During the laser spraying process, the cubic boron nitride powder undergoes a phase transformation, forming a composite coating that simultaneously possesses cubic boron nitride and hexagonal boron nitride. During the laser spraying process, the conversion of cBN to hBN allows cBN and hBN to work synergistically, thereby obtaining a composite coating that balances hardness and lubrication performance. Using cBN as a raw material, it can only be converted into hBN under the action of the laser beam 12. Direct conversion simplifies the process and achieves better bonding. The prepared coating simultaneously possesses both hardness and lubrication performance.

[0029] The resulting cubic boron nitride and hexagonal boron nitride content ratio is 60%-70%: 30%-40%. Specifically, by further controlling the content of cubic boron nitride and hexagonal boron nitride, cBN conversion can be achieved, resulting in a composite coating that is jointly reinforced by the hard particulate phase and the solid lubricating phase, thus achieving integrated friction reduction and wear resistance.

[0030] This invention employs a flat-plate ultrasonic-assisted ultra-high-speed laser cladding device 1, the schematic diagram of which is shown below. Figure 1 As shown, a high-speed reciprocating platform is used to achieve ultra-high speed by utilizing its high linear speed. The ultrasonic transducer 21 of the ultrasonic equipment is mounted on the high-speed reciprocating platform 24, and a clamp 23 is designed at the ultrasonic tool head 22 of the ultrasonic transducer 21 to hold the substrate 3, so that the ultrasonic waves 25 act on the coating on the substrate, thereby achieving the preparation of a flat plate ultrasonic-assisted ultra-high-speed laser cladding coating. Figure 1 As shown, the high-speed reciprocating platform 24 performs high-speed reciprocating motion in the horizontal direction. Before the experiment begins, the stroke and speed of the high-speed reciprocating platform 24 are set. During the coating preparation process, the laser head remains horizontally stationary, and its position is set at the midpoint formed by the high-speed reciprocating platform 24. Turning on the laser allows for the preparation of a single-pass laser cladding coating.

[0031] To meet the requirements for large-area coating fabrication, the laser head needs to move back and forth during the coating fabrication process. This requires calculating the single-pass time of the reciprocating platform (reciprocating platform stroke / reciprocating platform speed) to move the laser head downwards. The reciprocating platform stroke is 50mm. Therefore, when the reciprocating platform speed is 200mm / s, i.e., the single-pass time is 0.4s, the laser head needs to move downwards a certain distance every 0.4s.

[0032] Example 1

[0033] CoCrNi-based medium-entropy alloy (spherical powder with a particle size of 40 μm and a purity of 99%) was mixed with cBN powder (irregularly shaped powder with a particle size of 40 μm and a purity of 99%), with cBN accounting for 18 wt% of the total powder. The mixture was ball-milled in a planetary ball mill for 2 hours to form a mixed powder with a ball-to-powder ratio of 3:1 and a rotation speed of 500 rpm. The TC11 titanium alloy substrate was polished with a grinding wheel to remove the oxide layer on the surface. After being wiped clean with alcohol, it was fixed on a high-speed reciprocating platform 24 with a clamp. The mixed powder 13, which had been dried at 110℃ for 50 min, was dried in a drying oven and cooled to room temperature before being added to the powder feeder 11. The coating was prepared using a coaxial powder feeding method. The powder feeding gas flow rate and the protective gas flow rate were adjusted to preset values. Argon gas (purity of 99.999%) was used as the protective gas. The powder feeding rate was selected as 1.4 r / min, and the protective gas flow rate was 8 L / min. To further reduce internal stress, the TC11 was preheated to 500℃. Coating preparation was performed using a fiber laser cladding system. The laser head was aligned with the TC11 titanium alloy surface to be clad using a robot controller, and then slightly tilted to create a 20° angle between the laser head and the surface. The robot controller was used to adjust the distance between the laser head and the substrate surface, ensuring the defocusing distance remained at 18mm. This ensured that the mixed powder 13 converged at the laser beam 12 convergence point. The coating overlap rate was set to 85%, as shown in the diagram. Figure 2 As shown, the overlapping part 4 Figure 2 As shown, (overlap rate is an important parameter affecting the surface roughness of cladding; this overlap method can effectively and fully melt the material and reduce internal stress). Turn on the high-speed reciprocating platform 24 and set the platform movement speed to 240 mm / s. Use the ultrasonic auxiliary control cabinet to set the ultrasonic output power to 80%, select external control, and let the program in the robot controller control the powder feeding switch. Set the laser power in the laser system to 2100W and the light emission waiting time to 2 seconds. After completing the above steps, start the program to prepare the composite coating. Observe the powder feeder 11, the protective gas, and the laser system during the cladding process.

[0034] Example 2

[0035] CoCrNi-based medium-entropy alloy (spherical powder with a particle size of 40 μm and a purity of 99%) was mixed with cBN powder (irregularly shaped powder with a particle size of 50 μm and a purity of 99%), with the cBN content being 15 wt% of the CoCrNi-based medium-entropy alloy. The mixture was ball-milled in a planetary ball mill for 3 hours to form a mixed powder, with a ball-to-powder ratio of 3:1 and a rotation speed of 300 rpm. The TC11 titanium alloy substrate was then polished with a grinding wheel to remove the surface oxide layer. After cleaning with alcohol, it was fixed in a high-pressure environment using a fixture. The high-speed reciprocating platform 24; the mixed powder 13, which has been dried at 100℃ for 60 min, is dried in a drying oven and cooled to room temperature, and then added to the powder feeder 11. The coating is prepared by coaxial powder feeding; the powder feeding gas flow rate and the protective gas flow rate are adjusted to the preset values. Argon gas (purity 99.999%) is used as the protective gas. The powder feeding rate is selected as 1.0 r / min and the protective gas flow rate is 6 L / min. In order to further reduce internal stress, TC11 is preheated at a preheating temperature of 400℃. Coating preparation was performed using fiber laser cladding equipment. The laser head was aligned with the TC11 titanium alloy surface to be clad using a robot controller, and then slightly tilted to create a 30° angle between the laser head and the surface. The robot controller was used to adjust the distance between the laser head and the substrate surface, maintaining a defocus of 20mm. This ensured that the mixed powder 13 converged at the laser beam 12 convergence point. The coating overlap rate was set to 90%. The high-speed reciprocating platform was activated, and its movement speed was set to 220mm / s. The ultrasonic output power was set to 70% using the ultrasonic auxiliary control cabinet, and external control was selected, with the powder feeding switch controlled by the robot controller program. The laser power in the laser system was set to 1800W, and the light emission waiting time was set to 2s. After completing the above steps, the program was started to prepare the composite coating. During the cladding process, the powder feeder 11, the protective gas, and the laser system were observed.

[0036] Example 3

[0037] CoCrNi-based medium-entropy alloy (spherical powder with a particle size of 40 μm and a purity of 99%) was mixed with cBN powder (irregularly shaped powder with a particle size of 15 μm and a purity of 99%), with the cBN content being 20 wt% of the CoCrNi-based medium-entropy alloy. The mixture was ball-milled in a planetary ball mill for 1.5 hours to form a mixed powder, with a ball-to-powder ratio of 3:1 and a rotation speed of 600 rpm. The TC11 titanium alloy substrate was then polished with a grinding wheel to remove the surface oxide layer. After cleaning with alcohol, it was fixed in a high-pressure environment using a fixture. The high-speed reciprocating platform 24; the mixed powder 13, which has been dried at 120℃ for 30 min, is dried in a drying oven and cooled to room temperature, and then added to the powder feeder 11. The coating is prepared by coaxial powder feeding. The powder feeding gas flow rate and the protective gas flow rate are adjusted to the preset values. Argon gas (purity 99.999%) is used as the protective gas. The powder feeding rate is selected as 2.0 r / min and the protective gas flow rate is 12 L / min. In order to further reduce internal stress, TC11 is preheated at a preheating temperature of 600℃. Coating preparation was performed using fiber laser cladding equipment. The laser head was aligned with the TC11 titanium alloy surface to be clad using a robot controller, and then slightly tilted to create a 10° angle between the laser head and the surface. The robot controller was used to adjust the distance between the laser head and the substrate surface, maintaining a defocus of 16mm. This ensured that the mixed powder 13 converged at the laser beam 12 convergence point. The coating overlap rate was set to 88%. The high-speed reciprocating platform was activated, and its movement speed was set to 250mm / s. The ultrasonic output power was set to 70% using the ultrasonic auxiliary control cabinet, and external control was selected, with the powder feeding switch controlled by the robot controller program. The laser power in the laser system was set to 2300W, and the light emission waiting time was set to 2s. After completing the above steps, the program was started to prepare the composite coating. During the cladding process, the powder feeder 11, the protective gas, and the laser system were observed.

[0038] Example 4

[0039] CoCrNi-based medium-entropy alloy (spherical powder with a particle size of 40 μm and a purity of 99%) was mixed with cBN powder (irregularly shaped powder with a particle size of 40 μm and a purity of 99%), with the cBN content being 18 wt% of the CoCrNi-based medium-entropy alloy. The mixture was ball-milled in a planetary ball mill for 2 hours to form a mixed powder, with a ball-to-powder ratio of 3:1 and a rotation speed of 500 rpm. The TC11 titanium alloy substrate was then polished with a grinding wheel to remove the surface oxide layer. After cleaning with alcohol, it was fixed in a high-pressure environment using a fixture. The high-speed reciprocating platform 24; the mixed powder 13, which has been dried at 110℃ for 50 min, is dried in a drying oven and cooled to room temperature, and then added to the powder feeder 11. The coating is prepared by coaxial powder feeding. The powder feeding gas flow rate and the protective gas flow rate are adjusted to the preset values. Argon gas (purity 99.999%) is used as the protective gas. The powder feeding rate is selected as 1.4 r / min and the protective gas flow rate is 8 L / min. In order to further reduce internal stress, TC11 is preheated at a preheating temperature of 500℃. Coating preparation was performed using fiber laser cladding equipment. The laser head was aligned with the TC11 titanium alloy surface to be clad using a robot controller, and then slightly tilted to create a 20° angle between the laser head and the surface. The robot controller was used to adjust the distance between the laser head and the substrate surface, maintaining a defocus of 18mm. This ensured that the mixed powder 13 converged at the laser beam 12 convergence point. The coating overlap rate was set to 85%. The high-speed reciprocating platform 24 was activated, and its movement speed was set to 200mm / s. The ultrasonic output power was set to 80% using the ultrasonic auxiliary control cabinet, and external control was selected, with the powder feeding switch controlled by the robot controller program. The laser power in the laser system was set to 2300W, and the light emission waiting time was set to 2s. After completing the above steps, the program was started to prepare the composite coating. During the cladding process, the powder feeder 11, the protective gas, and the laser system were observed.

[0040] Example 5

[0041] CoCrNi-based medium-entropy alloy (spherical powder with a particle size of 40 μm and a purity of 99%) was mixed with cBN powder (irregularly shaped powder with a particle size of 40 μm and a purity of 99%), with the cBN content being 18 wt% of the CoCrNi-based medium-entropy alloy. The mixture was ball-milled in a planetary ball mill for 2 hours to form a mixed powder, with a ball-to-powder ratio of 3:1 and a rotation speed of 500 rpm. The TC11 titanium alloy substrate was then polished with a grinding wheel to remove the surface oxide layer. After cleaning with alcohol, it was fixed in a high-pressure environment using a fixture. The high-speed reciprocating platform 24; the mixed powder 13, which has been dried at 110℃ for 50 min, is dried in a drying oven and cooled to room temperature, and then added to the powder feeder 11. The coating is prepared by coaxial powder feeding. The powder feeding gas flow rate and the protective gas flow rate are adjusted to the preset values. Argon gas (purity 99.999%) is used as the protective gas. The powder feeding rate is selected as 1.4 r / min and the protective gas flow rate is 8 L / min. In order to further reduce internal stress, TC11 is preheated at a preheating temperature of 500℃. Coating preparation was performed using fiber laser cladding equipment. The laser head was aligned with the TC11 titanium alloy surface to be clad using a robot controller, and then slightly tilted to create a 20° angle between the laser head and the surface. The robot controller was used to adjust the distance between the laser head and the substrate surface, maintaining a defocus of 18mm. This ensured that the mixed powder 13 converged at the laser beam 12 convergence point. The coating overlap rate was set to 85%. The high-speed reciprocating platform 24 was activated, and its movement speed was set to 250mm / s. The ultrasonic output power was set to 80% using the ultrasonic auxiliary control cabinet, and external control was selected, with the powder feeding switch controlled by the robot controller program. The laser power in the laser system was set to 1800W, and the light emission waiting time was set to 2s. After completing the above steps, the program was started to prepare the composite coating. During the cladding process, the powder feeder 11, the protective gas, and the laser system were observed.

[0042] Comparative Example 1

[0043] Compared with Example 1, the high-speed reciprocating platform 24 is turned on and the platform moving speed is set to 180 mm / s. Other steps are the same as in Example 1.

[0044] Comparative Example 2

[0045] Compared with Example 1, the high-speed reciprocating platform 24 is turned on and the platform moving speed is set to 280 mm / s. Other steps are the same as in Example 1.

[0046] Comparative Example 3

[0047] Compared to Example 1, the cBN content was 10 wt% of the CoCrNi-based medium-entropy alloy, and the other steps were the same as in Example 1.

[0048] Comparative Example 4

[0049] Compared to Example 1, the cBN content was 25 wt% of the CoCrNi-based medium-entropy alloy, and the other steps were the same as in Example 1.

[0050] The average hardness and coefficient of friction of the composite coatings obtained in Examples 1-5 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1 below.

[0051] Table 1. Test results of average hardness and coefficient of friction of the composite coatings obtained in Examples 1-5 and Comparative Examples 1-4.

[0052]

[0053] As shown in Table 1 above, while moderate conversion slightly reduces the hardness of the coating, it significantly reduces wear. However, excessive conversion leads to a severe decrease in hardness and damages the coating performance. By adjusting the process parameters of ultra-high-speed laser cladding and controlling the heat input of the laser heat source to cBN, TiN and hBN reinforcing phases are generated in the coating, thereby obtaining a composite coating jointly reinforced by the hard particle phase and the solid lubricating phase.

[0054] Ultrasonic assistance ensures uniform distribution of ceramic particles, effectively avoiding problems such as uneven particle distribution and agglomeration. At the same time, by adjusting the ultrasonic assistance power, the conversion of cBN to hBN can be controlled.

[0055] The HRTEM and FFT tests were performed on Example 1, Comparative Example 1, and Comparative Example 2, and the test results are as follows: Figure 3 As shown, it can be seen that the conversion of cBN can be effectively controlled by changing the process.

[0056] Since different products have different requirements for hardness and lubrication performance, this application designs three different coatings. The first coating, prepared in Example 1, requires both high levels of hardness and lubrication performance. The second coating, prepared in Example 2, requires even higher hardness, with a slight decrease in lubrication performance. The third coating, prepared in Example 3, requires even higher lubrication performance, with a slight decrease in hardness. Different products can be selected according to the different application requirements of the coating.

[0057] The hardness and friction coefficient of the composite coatings obtained in Examples 1, 4, and 5 were plotted as follows: Figure 4 The trend chart, in Figure 4As can be seen, the distance between the average hardness point value and the friction coefficient point value is the largest in Example 1. In other words, Example 1 can achieve the maximum balance between hardness and friction coefficient. Although Example 4 has a smaller friction coefficient, its hardness is also smaller. In Example 5, the hardness is increased, but the friction coefficient is also increased. Neither Example 4 nor Example 5 can reach the optimal balance point.

[0058] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for producing a laser cladding composite coating, characterized in that The raw material of the composite coating comprises cubic boron nitride powder, and the composite coating is prepared on a base material by using a laser cladding technology; under the action of the laser, the cubic boron nitride powder generates phase transition to form the composite coating with cubic boron nitride and hexagonal boron nitride; In the process of the laser cladding, a physical field is arranged to assist the cubic boron nitride powder to generate phase transition; The physical field is ultrasonic assistance provided by an ultrasonic device, and the output power of the ultrasonic device is 70%-80%; The base material is titanium alloy; The content ratio of the cubic boron nitride and the hexagonal boron nitride formed is 60%-70%:30%-40%; The raw material of the composite coating further comprises chromium-nickel alloy powder; the chromium-nickel alloy powder is mixed with the cubic boron nitride powder and then ground to form mixed powder; and the mixed powder is used as the raw material of the composite coating to perform laser cladding; The addition amount of the cubic boron nitride powder is 15wt%-20wt% of the chromium-nickel alloy powder; The process parameters of the laser cladding are as follows: the laser power is set to 1800W-2300W, the scanning speed is 220-250mm / s, and the overlapping rate is 85%-90%.

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