Ultrasonic rolling-supersonic flame spraying composite modification method for titanium alloy and composite structure

Abstract

The invention discloses an ultrasonic rolling-supersonic flame spraying composite modification method for titanium alloy and a composite structure, and belongs to the technical field of metal surface modification.The method comprises the following steps that firstly, the to-be-strengthened surface of a titanium alloy matrix is ground, and machining marks are ground away; 2, the titanium alloy matrix is cleaned, and residues attached to the ground surface are removed; step 3, rolling the to-be-strengthened surface of the titanium alloy matrix; 4, the titanium alloy matrix is cleaned, and dirt on the surface of the titanium alloy matrix is washed away; 5, a WC-10Co-4Cr coating is sprayed on the surface, obtained after ultrasonic rolling, of the titanium alloy base body through the high velocity oxy-fuel spraying technology; and 6, the surface of the coating is ground and polished. The wear resistance, hardness and other comprehensive performance of the titanium alloy are improved, and the problems that the wear resistance of the titanium alloy is poor, and the surface is prone to being abraded are solved.

Description

Technical Field

[0001] This invention belongs to the field of metal surface modification technology, and relates to a method for modifying the surface of titanium alloys, and more particularly to a method and composite structure for ultrasonic rolling-supersonic flame spraying composite modification of titanium alloys. Background Technology

[0002] Titanium alloys possess superior properties, including high specific strength and specific stiffness, as well as thermal stability; strong corrosion resistance, resistant to corrosion and oxidation; and good biocompatibility, being harmless to human tissues. Moreover, they are abundant in resources, leading to their widespread application. However, titanium alloys have relatively low hardness, generally not exceeding HV350, are susceptible to adhesive wear, and exhibit poor surface fatigue and wear resistance, which limits their application to some extent. This is especially true in aircraft landing gear, where they endure severe frictional wear during prolonged service.

[0003] Surface modification technology for titanium alloys can significantly improve their wear resistance, surface hardness, fatigue resistance, and corrosion resistance, thereby expanding their application range and extending their service life. Traditional spray coatings (such as WC10Co4Cr) often exhibit porosity and microcracks at the interface with the titanium alloy substrate, resulting in low bonding strength. Thermal stress during spraying can easily cause coating peeling, and the substrate surface lacks a gradient reinforcement layer, limiting fatigue life. Conventional HVOF sprayed WC10Co4Cr coatings have a porosity >2%, making it difficult to meet the wear resistance requirements of extreme working conditions. Summary of the Invention

[0004] This invention provides a method and composite structure for ultrasonic rolling-supersonic flame spraying composite modification of titanium alloys, in order to overcome the shortcomings of the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for ultrasonic rolling-supersonic flame spraying composite modification of titanium alloys, comprising the following steps: Step 1, grinding the surface of the titanium alloy substrate to be strengthened to remove machining marks; Step 2, cleaning the titanium alloy substrate to remove residues adhering to the surface after grinding; Step 3, rolling the surface of the titanium alloy substrate to be strengthened; Step 4, cleaning the titanium alloy substrate to remove surface contaminants, i.e., removing oily media used for lubrication during rolling and contaminants such as metal residues adhering to the surface; Step 5, spraying a WC-10Co-4Cr coating onto the surface of the titanium alloy substrate after ultrasonic rolling using supersonic flame spraying technology; Step 6, polishing the coating surface.

[0006] To optimize the above technical solution, the specific measures also include: Furthermore, in step 1, the titanium alloy substrate surface to be strengthened is polished in multiple stages using 320-2000 grit sandpaper. The polishing direction is initially along the main stress direction of the titanium alloy substrate. After changing to sandpaper of different grits, the subsequent polishing direction is adjusted to ensure that the surface scratches caused by the previous grit are completely eliminated, thereby obtaining a pre-treated surface with uniform microstructure and no cross scratches, so as to avoid becoming a stress concentration source.

[0007] Furthermore, the specific process of grinding in step 1 is as follows: first, the surface of the titanium alloy substrate to be strengthened is ground to a surface roughness Ra of 1.0~1.2 μm, and then the surface roughness Ra is ground to a surface roughness Ra of 0.6~0.8 μm using a cross-linear grinding method.

[0008] Furthermore, in step 2, anhydrous ethanol is used as the cleaning medium to perform ultrasonic cleaning on the titanium alloy substrate after grinding in step 1, so as to thoroughly remove contaminants such as grinding debris and oil stains attached to the surface and ensure surface cleanliness.

[0009] Furthermore, in step 3, the titanium alloy substrate cleaned in step 2 is rolled using a Hawker ultrasonic rolling device. By rolling the surface of the titanium alloy substrate, a gradient nanostructure is constructed on its surface.

[0010] Further, the rolling process parameters in step 3 are as follows: static pressure is 500~1400 N; amplitude is 5.5~8.5 μm; feed speed is 0.04~0.1 mm / r; number of rolling cycles is 1~5; frequency is 25~30 KHz, preferably 28 KHz; spindle speed is 180~220 r / min, preferably 200 r / min.

[0011] Furthermore, in step 5, the HV-8000 supersonic flame spraying system is used for supersonic flame spraying.

[0012] Further, the supersonic flame spraying process parameters in step 5 are as follows: the fuel is oxygen, the oxygen flow rate is 20~30 L / h, preferably 24 L / h; the fuel is aviation kerosene, the aviation kerosene flow rate is 800~900 L / h, preferably 837 L / h; the powder feed rate is 25~35 g / min, preferably 30 g / min; the gun distance is 300~400 mm, preferably 360 mm; the gun movement speed is 450~550 mm / s, preferably 500 mm / s; and the WC-10Co-4Cr powder particle size is 15~45 μm.

[0013] Furthermore, in step 6, the coating surface is polished with 1000-2000 grit sandpaper until the surface roughness Ra is 0.4-0.8 μm to reduce the coefficient of friction and reduce surface defects.

[0014] Secondly, the present invention also provides a titanium alloy / WC10Co4Cr coating composite structure prepared by the above-mentioned ultrasonic rolling-supersonic flame spraying composite modification method.

[0015] The beneficial effects of this invention are as follows: This invention provides a method and structure for ultrasonic rolling-supersonic flame spraying composite modification of titanium alloys. Ultrasonic rolling treatment is used to improve the bonding force and wear resistance between the titanium alloy and the coating. By combining composite surface modification methods, stress concentration at the interface between the titanium alloy and the coating is reduced, thereby reducing the risk of microcracks and peeling caused by stress concentration in the coating, which is beneficial to improving the service life of the titanium alloy.

[0016] Specifically, this invention utilizes the synergistic effect of ultrasonic rolling and spraying to induce high-frequency impact plastic deformation, resulting in intense dislocation slip and dynamic recrystallization on the surface of the titanium alloy substrate, forming a continuous gradient structure from the surface nanocrystals. During flame spraying, significant residual stress can easily be generated between the coating and the substrate due to thermal gradients and rapid cooling effects. Ultrasonic rolling pretreatment effectively reduces residual stress generated during spraying by homogenizing the stress distribution within the substrate beforehand, resulting in a more uniform and stable internal microstructure and reducing the risk of microcracks and delamination caused by stress concentration. This not only improves the surface roughness and chemical activity of the substrate but also significantly increases the mechanical bonding and metallurgical adhesion between the coating and the substrate by forming a gradient nanostructure. This treatment allows the WC-10Co-4Cr coating to adhere more firmly to the substrate during subsequent spraying, improving the bond strength between the two. Due to the combined effect of the gradient nanostructure and reduced residual stress, the hardness and density of the coating are enhanced. This not only enables the coating to exhibit higher wear resistance under friction and impact environments, but also extends the service life of the coating, meeting the requirements for wear resistance under high-intensity working conditions.

[0017] This invention can solve the problems of poor wear resistance and easy surface wear of titanium and titanium alloys, thereby effectively expanding the application range of titanium alloys in the aerospace field, improving the overall performance of titanium alloys for aerospace, and playing an important role in the application of titanium alloys in the aerospace field. Attached Figure Description

[0018] Figure 1 These are corrosion microstructure diagrams of the titanium alloy substrate (a) and the substrate after ultrasonic rolling treatment (b) in the embodiment. Figure 2 These are cross-sectional topographic images of the coatings in Example (b) and Comparative Example 2 (a); Figure 3 These are cross-sectional hardness and surface hardness diagrams of the coating and substrate in the embodiments; Figure 4These are friction and wear diagrams of the materials in Examples 1, 2, and 3 under different working conditions. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments.

[0020] Example This embodiment provides a method for ultrasonic rolling-supersonic flame spraying composite modification of titanium alloys, including the following steps: Step 1: Pre-treatment of the substrate. The titanium alloy surface to be strengthened is finely ground and polished to reduce the surface roughness from the initial Ra of 1.6~2.0μm to Ra of 1.0~1.2μm. The cross-linear grinding method (alternating between 0° and 90°) is used to further reduce Ra to 0.6~0.8μm. The purpose is to remove surface processing marks, oxide scale and other impurities, ensure that the substrate surface reaches a uniform and smooth state, and eliminate micro-stress concentration sources.

[0021] Step 2: Use an alcohol solution to ultrasonically clean the polished titanium alloy for 10-30 minutes to thoroughly remove oil, dust, and residue left after polishing. Then, vacuum dry it to prepare for subsequent ultrasonic rolling.

[0022] Step 3: Ultrasonic rolling treatment. The rolling process parameters are shown in Table 1.

[0023] Table 1 Rolling process parameters

[0024] Step 4: Clean again after sanding to ensure that no residual abrasive or contaminants affect the coating quality.

[0025] Step 5: Supersonic flame spraying. The spraying process parameters are shown in Table 2.

[0026] Table 2 Spraying process parameters

[0027] Step 6: Perform surface grinding and polishing on the coated workpiece to eliminate any minor defects and unevenness on the coating surface, further improving surface smoothness and uniformity. For surface grinding, use 1000-1500 grit sandpaper and a polymer polishing cloth. For rough polishing, use a polishing slurry with a W2.5 particle size. Maintain the polishing machine speed at 500 rpm and polish with the slurry for about five minutes. Then, perform fine polishing with a silica suspension polishing slurry. Avoid excessive force during the entire polishing process to prevent scratching the surface. After polishing, thoroughly clean with alcohol. The cross-section of the polished workpiece should achieve a completely mirror-like finish. Surface grinding and polishing not only optimizes the appearance of the coating but also reduces surface stress concentration, contributing to higher stability and long-term durability of the reinforced layer in practical applications.

[0028] Comparative Example 1 This comparative example provides a method for modifying titanium alloys, which is basically the same as the example, except that step 5 is not performed, that is, only the titanium alloy matrix is ​​subjected to ultrasonic rolling treatment.

[0029] Comparative Example 2 This comparative example provides a method for modifying titanium alloys, which is basically the same as the example, except that steps 3 and 4 are not performed, that is, only the titanium alloy substrate is subjected to supersonic flame spraying treatment.

[0030] The titanium alloy matrix and the microstructure of TC6 after ultrasonic rolling treatment in the embodiment are as follows: Figure 1 As shown in the figure, compared to the titanium alloy matrix, the ultrasonically rolled material exhibits a microstructure gradient from the surface inwards. At the outermost layer, due to the most intense strain rate and plastic deformation, grain refinement occurs, forming a dense fine-grained / ultra-fine-grained layer. As the material extends inwards, the strain energy density decreases, and the degree of plastic deformation gradually weakens.

[0031] The morphology of the WC coating at the TC interface in Examples 1 and 2 are as follows: Figure 2 As shown in the figure, compared with the interface without ultrasonic rolling treatment, ultrasonic rolling transforms the interface into a serrated mechanically interlocked structure. This morphology originates from the matrix plastic flow induced by ultrasonic impact, which enhances the interfacial bonding force by "wrapping" and "interlocking" the bottom of the coating, surpassing the state of the original interface that relies solely on physical adsorption and limited metallurgical bonding.

[0032] The microhardness curves of the WC coating and the TC6 section in the example are as follows: Figure 3 As shown in the figure, the coating hardness is above 1200 HV, while the substrate exhibits gradient hardness. Ultrasonic rolling generates high strain and a sharp increase in dislocation density on the surface, which may lead to subcrystallineing / dynamic recrystallization. The reduced grain size results in increased yield strength and hardness. Compared with the hardness inside the substrate, there is a significant improvement.

[0033] The materials obtained in the examples and comparative examples were subjected to friction and wear tests under different working conditions. The curves of the friction coefficient of each material under different working conditions as a function of sliding time (or sliding distance) are shown below. Figure 4 As shown in the results, all six friction and wear curves exhibit typical friction and wear characteristics of first rising and then stabilizing, but there are significant differences between different working conditions. Under a load of 30N, the untreated TC6 substrate has a relatively high overall friction coefficient, with significant curve fluctuations, indicating severe interfacial wear, unstable friction behavior, and poor wear resistance. In contrast, the substrate treated with ultrasonic rolling has a significantly lower friction coefficient than the original substrate, and the fluctuation is reduced, indicating that surface densification and the introduction of residual compressive stress effectively improve its wear resistance. For the coating system, the WC-10Co-4Cr coating significantly improves the interfacial load-bearing capacity and reduces the shear stress in the actual contact area. Its friction coefficient curve shows better stability than that of the substrate under different loads. Under higher loads, the coated samples exhibit lower and more stable friction coefficients, which is related to the fact that high loads promote rapid oxidation of surface debris and the formation of a stable and dense oxide film. This film has solid lubrication properties and can significantly reduce interfacial shear resistance. Furthermore, the coefficient of friction of the coated sample after ultrasonic rolling treatment was further reduced, and its fluctuation range was smaller. This indicates that ultrasonic rolling treatment significantly improved the density and bonding strength of the coating-substrate interface, making the coating less prone to peeling under high loads and the stress distribution more uniform. This resulted in better wear resistance and friction stability throughout the entire wear stage.

[0034] In this invention, unless otherwise stated, scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, the reagents, materials, and procedures used herein are all widely used in the relevant fields.

[0035] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for ultrasonic rolling-HVAF composite modification of titanium alloy, characterized in that it comprises the following steps: Step 1: polishing the surface of the titanium alloy substrate to be strengthened to remove machining marks; Step 2: cleaning the titanium alloy substrate to remove residues adhered to the surface after polishing; Step 3: rolling the surface of the titanium alloy substrate to be strengthened; Step 4: cleaning the titanium alloy substrate to remove surface stains; Step 5: using the HVAF technology to spray a WC-10Co-4Cr coating on the surface of the titanium alloy substrate after ultrasonic rolling; Step 6: polishing the coating surface.

2. The method for ultrasonic rolling-HVAF composite modification of titanium alloy according to claim 1, characterized in that in step 1, the surface of the titanium alloy substrate to be strengthened is polished in multiple stages using 320-2000 grit sandpaper, and the polishing direction is first along the main stress direction of the titanium alloy substrate, and after changing the sandpaper with different grits, the subsequent polishing direction is adjusted.

3. The method for ultrasonic rolling-HVAF composite modification of titanium alloy according to claim 2, characterized in that the specific process of step 1 is: first polish the surface of the titanium alloy substrate to be strengthened to a surface roughness Ra of 1.0-1.2 μm, and then polish to a surface roughness Ra of 0.6-0.8 μm using the cross linear polishing method.

4. The method for ultrasonic rolling-HVAF composite modification of titanium alloy according to claim 1, characterized in that in step 2, anhydrous ethanol is used as the cleaning medium to ultrasonically clean the titanium alloy substrate after step 1 polishing.

5. The method for ultrasonic rolling-HVAF composite modification of titanium alloy according to claim 1, characterized in that in step 3, the titanium alloy substrate after step 2 cleaning is rolled using a Hauker ultrasonic rolling device.

6. The method for ultrasonic rolling-HVAF composite modification of titanium alloy according to claim 5, characterized in that the rolling process parameters of step 3 are: static pressure 500-1400 N; amplitude 5.5-8.5 μm; feed speed 0.04-0.1 mm / r; rolling times 1-5; frequency 25-30 KHz; spindle speed 180-220 r / min.

7. The method for ultrasonic rolling-HVAF composite modification of titanium alloy according to claim 1, characterized in that in step 5, the HV-8000 type HVAF spraying system is used for HVAF spraying.

8. The method for ultrasonic rolling-HVAF composite modification of titanium alloy according to claim 1, characterized in that ​ ​ ​ ​ ​ ​ ​ The supersonic flame spraying process parameters of step 5 are as follows: the fuel gas is oxygen, the flow rate of oxygen is 20-30 L / h; the fuel is aviation kerosene, the flow rate of aviation kerosene is 800-900 L / h; the powder feeding amount is 25-35 g / min; the gun distance is 300-400 mm, the gun moving speed is 450-550 mm / s; and the WC-10Co-4Cr powder particle size is 15-45 μm. 9.The ultrasonic roll bonding-supersonic flame spraying composite modification method for titanium alloy according to claim 1, characterized in that: In step 6, the coating surface is polished by using 1000-2000 mesh sandpaper until the surface roughness Ra is 0.4-0.8 μm. 10.The titanium alloy / WC10Co4Cr coating composite structure prepared by the ultrasonic roll bonding-supersonic flame spraying composite modification method according to any one of claims 1-9.

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