Hexagonal close-packed micro-frame structure on titanium alloy surface and preparation method thereof

Abstract

The preparation method comprises the following steps: (1) adopting a picosecond laser process, selecting a tungsten-cobalt hard alloy CD650 with excellent high-temperature mechanical properties as a mold material, and etching a periodic hexagonal densely-arranged micron-scale bulge structure on the surface of the mold material; and (2) the CD650 micro-mold is adopted, Ti6Al4V (TC4) titanium alloy is imprinted at a certain temperature and pressure, and a periodic hexagonal close-packed micro-frame structure complementary with the micro-mold structure is obtained on the surface of the titanium alloy. The micro-mold machined through laser etching is high in precision, and the microstructures are arranged in order; the microstructure of the die after micro-imprinting can be accurately copied to the surface of the titanium alloy, and the forming quality of the microstructure of the titanium alloy is good. The method for preparing the microstructure on the surface of the material by combining the laser etching micro-mold with the micro-imprinting is high in precision, low in cost, high in efficiency and suitable for large-scale preparation of the microstructure on the surface of most metal and non-metal materials.

Description

Technical Field

[0001] The invention relates to the field of micro-nano structure processing and forming, and in particular to a titanium alloy surface hexagonal close-packed micro-frame structure and a preparation method thereof. Background Art

[0002] In current research reports, common preparation methods for micro-nano structures include etching (chemical etching, laser etching, mechanical etching, photolithography), deposition (chemical vapor deposition, electrochemical deposition), sol-gel method and micro-imprinting method. Among them, laser etching can be divided into nanosecond laser etching, picosecond laser etching and femtosecond laser etching according to the length of laser pulse width. This method is universal and can be applied to the surface of most solid materials. It has high etching accuracy and can etch rich microstructure patterns. However, the cost of laser etching alone is high, especially picosecond laser and femtosecond laser etching, which is not suitable for large-scale preparation of micro-nano structures on the surface of materials. Micro-imprinting method is a preparation process that uses templates as the main structure and obtains micro-nano structures by controlling and adjusting the morphology and size of the template. This method is simple, low-cost and efficient, and is more suitable for large-scale preparation of microstructures. Therefore, the present invention adopts a method of laser etching micro-mold combined with micro-embossing to prepare microstructures on the surface of high-hardness metal materials. A high-precision micro-mold is etched with a picosecond laser, which is used as a micro-embossing template. Then, the high-hardness metal material is micro-embossed at a certain temperature and pressure. The micro-mold can be reused, thereby reducing the cost of microstructure preparation and promoting large-scale production.

[0003] At present, the application of micro-embossing method to prepare microstructures is mainly concentrated on the surfaces of polymers and low-hardness metal materials (pure copper, magnesium alloy, aluminum alloy, etc., with hardness of 60~100 HV). The imprinting temperature of these materials is low (room temperature to 250°C) and the imprinting pressure is small, so the micro-mold morphology structure can be easily accurately replicated on the surface of the pressed material.

[0004] Titanium alloy is a metal material with high specific strength, high thermal strength, good corrosion resistance and biocompatibility. Based on these excellent properties, titanium alloy is widely used in aerospace, marine engineering, biomedicine, pipeline transportation and other fields. Titanium alloy itself is a hydrophilic material. When it is used as the surface material of equipment such as pipelines or hulls, it is easy to freeze in cold weather; titanium alloy has good biocompatibility. When it is used in marine equipment, microorganisms, algae and animals in the ocean are more likely to attach to the surface of the equipment, causing serious marine biofouling problems. Constructing micro-nano structures on the surface of titanium alloy can give titanium alloy hydrophobic or super-hydrophobic properties, so that the surface of the material has the functions of self-cleaning, marine drag reduction, anti-fouling and corrosion inhibition, anti-fogging and anti-freezing, etc., and has broad application prospects in inhibiting ice formation and slowing down marine biofouling.

[0005] The surface hardness of titanium alloy materials is 300~400 HV, which is much higher than the hardness of low-hardness non-ferrous metal materials such as polymers and magnesium, aluminum and copper. Therefore, when using micro-embossing method to prepare microstructures on the surface of titanium alloy, higher embossing temperature and pressure are required, which puts higher requirements on the mechanical properties of micro-molds and greatly increases the difficulty of processing micro-molds. Currently, there are few reports on the preparation of microstructures on the surface of titanium alloys by micro-embossing technology. From the perspective of saving costs and improving efficiency, the present invention uses laser etching of high-hardness micro-molds combined with hot micro-embossing to prepare microstructures on the surface of Ti6Al4V titanium alloy, filling the lack of related research. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings and deficiencies of the above-mentioned prior art and to provide a titanium alloy surface hexagonal close-packed micro-frame structure and a preparation method thereof.

[0007] The present invention is achieved through the following technical solutions: A method for preparing a hexagonal close-packed micro-frame structure on a titanium alloy surface comprises the following steps: Step (1): selecting a high-hardness cemented carbide material as a micro-mold blank, and designing a laser etching pattern having a micro-protrusion structure complementary to the micro-frame structure; Step (2): performing surface polishing on the micro mold blank before laser etching; Step (3): laser etching the micro-mold blank processed in step (2) according to the pattern designed in step (1) to obtain a cemented carbide micro-mold with a micro-convex structure; ultrasonically cleaning the obtained cemented carbide micro-mold with acetone and deionized water in turn, and drying it for standby use; Step (4): before micro-embossing, the Ti6Al4V titanium alloy is surface polished, and after polishing, a layer of boron nitride spray-type mold release agent is sprayed on the surface of the Ti6Al4V; Step (5): using the cemented carbide micro-mold obtained in step (3) to micro-emboss the Ti6Al4V titanium alloy treated in step (4); ultrasonically cleaning the micro-embossed Ti6Al4V titanium alloy with acetone and deionized water in sequence, and drying, to obtain a titanium alloy surface with a hexagonal close-packed micro-frame structure.

[0008] The cemented carbide material in step (1) is tungsten-cobalt cemented carbide CD650, which has a composition of 86 wt.% tungsten carbide and 14 wt.% cobalt.

[0009] The laser-etched micro-mold pattern designed in step (1) is a regular hexagon.

[0010] In step (2), the polishing agent used in the polishing process is a water-soluble W2.5 diamond grinding paste, and the micro-mold blank is polished until the surface is mirror-smooth.

[0011] In the laser etching process of step (3), the laser etching equipment used is an infrared picosecond laser Ablator-PNIR-50, whose central wavelength is 1064 nm, pulse width is <15 ps, and theoretical spot diameter after focusing is 17 μm; the laser repetition frequency is 500 kHz, the scanning speed is 100 mm / s, and the laser etching power is 5-6 W; the side length of the unit regular hexagon in the etching pattern is 40 μm, and the number of scans is 20 times; the laser focusing state is defocused, and the defocus amount is 0.5-0.6 mm.

[0012] The ultrasonic cleaning time in step (3) is 5 min.

[0013] In the micro-embossing process of step (5), the hot pressing equipment used is ZT-40-20Y, with a rated power of 40 kW, a rated temperature of 2100 °C, and a limit vacuum of 10 -4 Pa, the maximum pressure is 20 t.

[0014] During the micro-embossing process in step (5), the hot embossing temperature used was 600 °C and the heating rate was 10 °C / min. After the temperature was maintained constant, the pressure was applied at a rate of 100 N / s to 100 kN, and the holding time was 2 min.

[0015] The ultrasonic cleaning time in step (5) is 10 min.

[0016] Compared with the prior art, the present invention has the following advantages and effects: The micro-mold processed by laser etching in the present invention has high precision and regular microstructure arrangement; the microstructure of the mold after micro-embossing can be accurately replicated on the titanium alloy surface, and the titanium alloy microstructure molding quality is good. This laser etching micro-mold combined with micro-embossing method is used to prepare microstructures on the material surface, with high precision, low cost and high efficiency, and is suitable for large-scale preparation of microstructures on the surfaces of most metal and non-metal materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the hexagonal structure pattern designed for laser etching.

[0018] Figure 2 This is Example 1, the surface morphology (a) and cross-sectional morphology (b) of the CD650 micro mold obtained by processing 30 μm-15 times under laser focusing state.

[0019] Figure 3 This is Example 2, the surface morphology (a) and cross-sectional morphology (b) of the CD650 micro mold obtained by processing 30 μm-15 times under laser defocus state.

[0020] Figure 4 This is Example 3, the surface morphology (a1) and cross-sectional morphology (a2) of the CD650 micro mold obtained by processing 40μm-20 times under laser defocus state; the surface morphology (b1) and the filling depth of the microstructure (b2) of the Ti6Al4V alloy after hot embossing; the surface morphology (c1) of the CD650 micro mold 40μm-20 times after one embossing and the comparison of the protrusion height of the micro mold cross section before and after embossing (c2). DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with specific embodiments.

[0022] The present invention firstly adopts a picosecond laser etching method to etch a hexagonal close-packed micro-protrusion structure, i.e., the first microstructure, on the surface of a tungsten-cobalt cemented carbide CD650, and uses it as a micro-mold to emboss a Ti6Al4V titanium alloy at a certain temperature and pressure to obtain a hexagonal close-packed micro-frame structure on the surface of the titanium alloy, i.e., the second microstructure. The present invention will be described in detail below in conjunction with three specific embodiments.

[0023] Embodiment 1: Step (1): Select high-hardness cemented carbide micro-mold material CD650 and design a laser etching pattern with a micro-convex structure, as shown in the schematic diagram Figure 1 shown.

[0024] Step (2): Before laser etching, the surface of the cemented carbide CD650 is polished using a water-soluble W2.5 diamond paste until the surface is mirror-smooth.

[0025] Step (3): According to the pattern designed in step (1), the surface of cemented carbide CD650 was etched using an infrared picosecond laser Ablator-PNIR-50. The central wavelength of the laser was 1064 nm, the pulse width was <15 ps, and the theoretical spot diameter after focusing was 17 μm. Before etching, the focus was adjusted to minimize the focused spot. The laser repetition frequency was 500 kHz, the scanning speed was 100 mm / s, and the laser etching power was 5-6 W. The side length of the regular hexagon in the etched pattern was 30 μm, and the number of laser scans was 15. After etching, the micro mold was cleaned in acetone and deionized water for 5 min each, and then dried for use.

[0026] According to the steps in Example 1, a micro-protrusion structure complementary to the micro-frame structure is obtained on the surface of CD650 cemented carbide after laser etching, and its surface morphology and cross-sectional morphology are as follows: Figure 2As shown in the figure, it can be found that after laser etching, the micro-protrusion structure on the cemented carbide surface is periodic hexagonal close-packed, the gap between the micro-protrusions and the top of the micro-protrusions is about 30 μm, and the height of the micro-protrusions is about 57 μm. However, the gap between the micro-protrusions and the top platform of the micro-protrusions is too narrow, which will bring difficulties to the filling rate of hot stamping. It is necessary to appropriately increase the gap between the top platforms.

[0027] Embodiment 2: The only difference between the steps of Example 2 and Example 1 is that in step (3), the laser focusing state is changed from focusing to defocusing, and the defocusing amount is 0.5-0.6 mm. The purpose of defocusing is to increase the gap between the micro-protrusion and the top platform of the micro-protrusion, and at the same time increase the inclination angle of the side wall of the micro-protrusion, thereby reducing the difficulty of stamping Ti6Al4V titanium alloy.

[0028] According to the steps in Example 2, the surface morphology and cross-sectional morphology of the CD650 cemented carbide micro-mold obtained after laser etching are as follows: Figure 3 As shown in (ab). It can be found that the inclination angle of the micro-protrusion side wall has increased, and the gap between the micro-protrusion and the top platform of the micro-protrusion has increased significantly, about 46 μm, which is about 53% higher than the focus state in Example 1, and the height of the micro-protrusion is about 58 μm. However, at this time, the top platform of the micro-protrusion is too sharp, which is not conducive to the subsequent pressure bearing and demolding of the titanium alloy, and the size of the microstructure needs to be further optimized.

[0029] Embodiment 3: In view of the problem that the top platform of the micro-protrusion of the micro-mold with a unit regular hexagon side length of 30 μm in Example 2 is too sharp and is not conducive to pressure bearing and demolding during hot pressing, the structure of the micro-mold is further optimized, mainly by keeping the defocus state of the laser unchanged, increasing the side length of the unit regular hexagon from 30 μm to 40 μm, and increasing the number of laser scans from 15 to 20 times. The specific implementation steps are as follows: Step (1): Select high-hardness cemented carbide micro-mold material CD650 and design a laser etching pattern with a micro-convex structure, as shown in the schematic diagram Figure 1 shown.

[0030] Step (2): Before laser etching, the surface of the cemented carbide CD650 is polished using a water-soluble W2.5 diamond paste until the surface is mirror-smooth.

[0031] Step (3): The side length of the regular hexagonal unit of the etching pattern in Example 2 was adjusted from 30 μm to 40 μm, and the number of laser scans was increased from 15 to 20 times, while other laser scanning parameters and focusing conditions remained unchanged. After laser etching, the micro mold was cleaned in acetone and deionized water for 5 min each, and dried for standby use.

[0032] The surface morphology and cross-sectional morphology of the CD650 micro mold obtained after laser etching according to the above three steps are shown in Figure 2. Figure 4 (a1-a2). It can be found that compared with the micro-mold obtained by laser defocusing 30 μm-15 times, the gap between the tops of the micro-protrusions of the microstructure obtained by laser defocusing 40 μm-20 times is about 48 μm, the height of the micro-protrusions is about 60 μm, and the pressure-bearing area of ​​the micro-protrusion structure is significantly increased. This micro-mold is subjected to less pressure during imprinting, is not easy to deform, and is more conducive to subsequent demolding. Therefore, the CD650 micro-mold obtained by laser defocusing 40 μm-20 times is used as the final imprinting template of the present invention, and the imprinting process of Ti6Al4V titanium alloy is carried out according to the following steps.

[0033] Step (4): before stamping, the Ti6Al4V titanium alloy is surface polished using a water-soluble W2.5 diamond paste as the polishing agent until the surface is mirror-smooth; after polishing, a layer of boron nitride spray-type mold release agent is sprayed on the surface of the Ti6Al4V.

[0034] Step (5): Using the 40 μm-20 micro mold etched in step (3) as a template, hot stamping the Ti6Al4V titanium alloy processed in step (4). The stamping temperature is increased to 600 °C at a rate of 10 °C / min, and then the stamping pressure is increased to 100 kN at a rate of 100N / s, and the pressure holding time is 2 min. After micro stamping, the titanium alloy is ultrasonically cleaned in acetone and deionized water for 10 min, and then dried.

[0035] The surface morphology and cross-sectional morphology of Ti6Al4V obtained after micro hot stamping according to the above experimental steps are as follows Figure 4 (b1-b2) shows the surface morphology after micro mold embossing. Figure 4 As shown in (c1), the height comparison of the protrusion of the micro mold section before and after embossing is Figure 4 (c2) As shown. It can be found that the surface morphology of Ti6Al4V titanium alloy after embossing is a hexagonal close-packed microframe structure complementary to the micro-mold structure, and the filling depth of the microstructure on the Ti6Al4V surface is about 40 μm. At the same time, it can be found that the surface morphology after micro-mold embossing has no obvious change compared with the height of the protrusion before embossing, indicating that this micro-mold can be reused. The above results show that the CD650 cemented carbide micro-mold obtained by laser defocusing 40 μm-20 times has good feasibility as a micro-embossing template for titanium alloy.

[0036] The surface of the CD650 cemented carbide micro-mold processed by picosecond laser etching in the present invention presents a hexagonal close-packed micro-convex structure, and the micro-structure forming precision is high and the morphology is regular. Ti6Al4V titanium alloy has a large hardness, and a high temperature of 600°C can soften it, reducing the yield strength during embossing molding, so that the micro-mold structure is easier to fill on the titanium alloy surface, and the micro-structure filling degree is improved. After hot embossing, the surface of the titanium alloy presents a hexagonal close-packed micro-frame structure, the micro-structure replication degree is high, and the molding quality is good. The surface and cross-sectional morphology of the micro-mold after one hot embossing are not significantly changed, and it can be reused many times. Therefore, the laser etching micro-mold combined with the micro-embossing method used in the present invention has great application potential in reducing the cost of micro-structure preparation, improving production efficiency, and promoting large-scale production, and is suitable for the preparation of surface micro-structures of most metals and non-metallic materials.

[0037] The present invention can change the structure of the corresponding micro-mold by adjusting the laser etching parameters and focusing conditions according to the requirements for the microstructure of the titanium alloy surface, thereby realizing the efficient preparation of various pattern microstructures.

[0038] In view of the current research status that micro-embossing technology is mainly used on the surfaces of polymers and low-hardness metals (pure copper, aluminum alloys, magnesium alloys, etc.), the present invention provides an effective reference and reference for the micro-embossing preparation of relatively high-hardness titanium alloys, making up for the lack of related research.

[0039] Table 1 Specific chemical composition of Ti6Al4V titanium alloy (wt.%)

[0040] The present invention is not limited by the above specific embodiments. Any simple modification and equivalent transformation made to the above embodiments without departing from the content and technical principle of the technical solution of the present invention still falls within the protection scope of the solution of the present invention.

Claims

1. A method for preparing a hexagonal close-packed microframe structure on a titanium alloy surface, characterized in that The following steps are involved: Step (1): selecting a high-hardness cemented carbide material as a micro-mold blank, and designing a laser etching pattern having a micro-protrusion structure complementary to the micro-frame structure; Step (2): performing surface polishing on the micro mold blank before laser etching; Step (3): laser etching the micro-mold blank processed in step (2) according to the pattern designed in step (1) to obtain a cemented carbide micro-mold with a micro-convex structure; ultrasonically cleaning the obtained cemented carbide micro-mold with acetone and deionized water in turn, and drying it for standby use; Step (4): before micro-embossing, the Ti6Al4V titanium alloy is surface polished, and after polishing, a layer of boron nitride spray-type mold release agent is sprayed on the surface of the Ti6Al4V; Step (5): using the cemented carbide micro-mold obtained in step (3) to micro-emboss the Ti6Al4V titanium alloy treated in step (4); ultrasonically cleaning the micro-embossed Ti6Al4V titanium alloy with acetone and deionized water in sequence, and drying, to obtain a titanium alloy surface with a hexagonal close-packed micro-frame structure.

2. The method for preparing the hexagonal close-packed micro-frame structure on the titanium alloy surface according to claim 1, characterized in that: The cemented carbide material in step (1) is tungsten-cobalt cemented carbide CD650, which has a composition of 86 wt.% tungsten carbide and 14 wt.% cobalt.

3. The method for preparing the hexagonal close-packed micro-frame structure on the titanium alloy surface according to claim 1, characterized in that: The laser-etched micro-mold pattern designed in step (1) is a regular hexagon.

4. The method for preparing the hexagonal close-packed micro-frame structure on the titanium alloy surface according to claim 1, characterized in that: In step (2), the polishing agent used in the polishing process is a water-soluble W2.5 diamond grinding paste, and the micro-mold blank is polished until the surface is mirror-smooth.

5. The method for preparing the hexagonal close-packed micro-frame structure on the titanium alloy surface according to claim 1, characterized in that: In the laser etching process of step (3), the laser etching equipment used is an infrared picosecond laser Ablator-PNIR-50, whose central wavelength is 1064 nm, pulse width is <15 ps, and theoretical spot diameter after focusing is 17 μm; the laser repetition frequency is 500 kHz, the scanning speed is 100 mm / s, and the laser etching power is 5-6 W; the side length of the unit regular hexagon in the etching pattern is 40 μm, and the number of scans is 20 times; the laser focusing state is defocused, and the defocus amount is 0.5-0.6 mm.

6. The method for preparing the hexagonal close-packed micro-frame structure on the titanium alloy surface according to claim 1, characterized in that: The ultrasonic cleaning time in step (3) is 5 min.

7. The method for preparing the hexagonal close-packed micro-frame structure on the titanium alloy surface according to claim 1, characterized in that: In the micro-embossing process of step (5), the hot pressing equipment used is ZT-40-20Y, with a rated power of 40 kW, a rated temperature of 2100 °C, and a limit vacuum of 10 -4 Pa, the maximum pressure is 20 t.

8. The method for preparing the hexagonal close-packed micro-frame structure on the titanium alloy surface according to claim 1, characterized in that: During the micro-embossing process in step (5), the hot embossing temperature used was 600 °C and the heating rate was 10 °C / min. After the temperature was maintained constant, the pressure was applied at a rate of 100 N / s to 100 kN, and the holding time was 2 min.

9. The method for preparing the hexagonal close-packed micro-frame structure on the titanium alloy surface according to claim 1, characterized in that: The ultrasonic cleaning time in step (5) is 10 min.

10. A titanium alloy surface hexagonal close-packed micro-frame structure, characterized in that Obtained by the preparation method according to any one of claims 1 to 9.

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