An inverted pyramid microstructure and a method for precisely preparing the same on a surface of TC4 titanium alloy

Abstract

The application discloses an inverted pyramid microstructure and a precise preparation method thereof on a TC4 titanium alloy surface; the application mainly utilizes a photoetching method to manufacture a silicon imprinting template of a microscale structure of a positive pyramid array on monocrystalline silicon, and high-temperature hot pressing forming is carried out on the TC4 titanium alloy by using the silicon imprinting template, so that the microscale structure of the inverted pyramid array is formed on the titanium alloy surface. The high-temperature hot-pressed titanium alloy microstructure obtained by the application has high size precision and good forming quality. The application determines a specific temperature and pressure range for the application of the hot pressing process of the microimprinting forming of the titanium alloy, and the high-temperature hot pressing forming method has the advantages of simple process, low cost, high efficiency and good formability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro process structure, and particularly relates to a reverse pyramid micro structure and a precise preparation method thereof on a TC4 titanium alloy surface. BACKGROUND

[0002] With the development of micro processing technology, the micro-imprinting process with environmental friendliness has attracted more and more attention. Micro-imprinting technology is a kind of precise imprinting technology based on physical forming method on the micron scale, which can imprint small structures and shapes on a specific surface. Its imprinting process needs to align the mold with the blank, load and hold for a certain time, and finally demold. Micro-imprinting process has great advantages in reducing production cost and shortening production cycle, and can realize the preparation of large-area micron array structure, and the prepared structure has good regularity and good industrial application prospect. At present, the research on micro-imprinting forming technology is mostly concentrated on relatively soft high polymer, such as polydimethylsiloxane (PDMS) film and polyethylene (PE) film. Micro-imprinting forming technology is less used in metal-based materials.

[0003] Compared with high polymer film materials, micro-imprinting of micron-scale microstructure on metal surface requires more precise temperature and pressure control. Micro-imprinting can be used to mold metal materials into specific shapes for manufacturing various precision parts, and can also be used to build micron-scale microstructure on metal surface to prepare special super-hydrophobic surface with wide application prospect. At present, a small number of studies have successfully imprinted microstructure on low-hardness metals such as aluminum, magnesium and copper alloy (temperature is room temperature to about 200℃, pressure is less than 10kN, surface microstructure replication precision is high, forming quality is good), and there are fewer studies on metals with hardness greater than aluminum alloy (such as titanium alloy).

[0004] Titanium and its alloys are a kind of metal materials with excellent corrosion resistance, high specific strength and good biocompatibility, but due to the relatively high hardness of titanium alloy, micro-imprinting at room temperature and low temperature is difficult, so the application of micro-imprinting technology on titanium alloy still needs to be developed. In the present application, 60kN pressure is used to try to imprint and form on the surface of TC4 titanium alloy under the temperature conditions (room temperature and 200℃) that can successfully micro-imprint and form on low-hardness metals, and the results are as follows Figure 1As shown, the microstructure imprint is not complete, the imprint depth is only 2-3 μm (the height of the template microstructure is about 15 μm), and the microstructure of the silicon wafer as the mold is also damaged. It is illustrated that the existing low-hardness metal micro-imprint forming process (room temperature and 200 DEG C) is not suitable for titanium alloy. Therefore, the present application attempts to solve this problem by using high-temperature hot pressing technology. The high-temperature hot pressing process can effectively change the microstructure of the metal, make the metal more softened, reduce the yield strength, make the micro-imprint process more easily realized, improve the precision of the micro-imprint, and can protect the brittle silicon imprint template from being damaged. Therefore, the high-temperature hot pressing technology has important practical application value in the field of micro-imprint. SUMMARY

[0005] The present application aims to overcome the shortcomings and deficiencies of the prior art, and provides a reverse pyramid microstructure and a method for precisely preparing the reverse pyramid microstructure on the surface of TC4 titanium alloy. The pyramid microstructure silicon imprint template prepared by the photolithography method has high size precision and can be repeatedly used; the hot forming method is simple in process, low in cost, high in efficiency and good in formability.

[0006] The present application is realized by the following technical scheme:

[0007] A method for precisely preparing a microstructure on the surface of high-hardness TC4 titanium alloy, comprising the following steps:

[0008] S100: manufacturing a silicon imprint template, wherein a first microstructure of a positive pyramid array is formed on the surface of the silicon imprint template;

[0009] S200: high-temperature hot pressing the TC4 titanium alloy by using the silicon imprint template, so as to form a second microstructure of a reverse pyramid array on the surface of the titanium alloy, which is complementary to the first microstructure of the positive pyramid array of the silicon imprint template.

[0010] In step S100, the silicon imprint template is processed by using photolithography and wet etching, and specifically comprises the following steps:

[0011] 101) preparing a silicon dioxide mask by using a photolithography method: a pre-designed pattern is prepared on the surface of the silicon wafer with an oxide layer by using a photolithography method, and the pattern is a square periodic array with a specific ratio of side length and pitch;

[0012] transferring the periodically arranged square photoresist pattern to the silicon dioxide layer by using BOE (49% HF: 40% NH4F = 1:6) for 3 min, and then dissolving the photoresist by using acetone for 7 min, so that the corrosion-resistant silicon dioxide layer serves as a real mask, and a silicon wafer covered with a square silicon dioxide mask is obtained;

[0013] 102) Wet etching: The TMAH solution is heated to 85°C, the silicon wafer covered with a square silicon dioxide mask is placed on a polytetrafluoroethylene basket and suspended in a 4% to 5% TMAH (tetramethylammonium hydroxide) solution, and etched for 35 min to 45 min to obtain a silicon wafer with a positive pyramid array microstructure covered with a silicon dioxide mask.

[0014] 103) Removal of silicon dioxide mask: Remove the polytetrafluoroethylene basket containing the etched silicon wafer from the TMAH solution, rinse with deionized water, then etch in BOE solution for 5 minutes, and rinse with deionized water to obtain a silicon imprint template with a positive pyramid micron structure.

[0015] Step 101) The ratio of the side length to the spacing of the silicon dioxide square mask is 2.5.

[0016] Step 102): During the wet etching process, magnetic stirring is applied at a speed of 60 r / min.

[0017] In step S200, the high-temperature hot pressing specifically includes the following steps:

[0018] 201) Sample Placement: Place the silicon imprint template with the microstructure onto the titanium alloy surface, then place the entire template into the hot imprint mold, and carefully place it into the hot press furnace. Close the hot press furnace and evacuate for 3×10⁻⁶ seconds. -3 MPa;

[0019] 202) Preloading process: The press loads 10kN at a rate of 100N / s as a preloading load to reduce the thermal rebound effect on the sample surface during hot pressing.

[0020] 203) Heating process: The sample is heated as a whole by the heating system of the press. The heating temperature is set to 600-700℃, and the heating rate is 10℃ / min. Slow heating ensures uniform heating of the sample and reduces the temperature difference between the sample and the set temperature.

[0021] 204) Hot pressing process: After reaching the set temperature, the TC4 titanium alloy with the silicon imprint template attached to the surface is loaded using the pressure system of the press. The loading rate is 100 N / s, the set pressure is 60 kN, and the pressure is held for 120 seconds. Slow pressure is applied to ensure uniform hot pressing of the sample, and the pressure holding process reduces the thermal rebound effect during hot pressing.

[0022] 205) Sample removal: After the hot pressing process is completed, the pressure is unloaded, and the sample is cooled to room temperature in the furnace. The titanium alloy sample is then removed, and its surface has an inverted pyramid microstructure.

[0023] Using the method described above in this invention, an inverted pyramid microstructure with a periodic array arrangement can be obtained.

[0024] Compared with the prior art, the present invention has the following advantages and effects:

[0025] This invention utilizes photolithography to prepare silicon templates, effectively transforming silicon substrates coated with periodic silica masks into regular, ordered, and highly repeatable pyramidal array silicon substrates. These silicon imprint templates exhibit high dimensional accuracy and are reusable.

[0026] This invention effectively solves the problem of difficult micro-imprinting of titanium alloys through high-temperature hot pressing technology. Microstructures can be directly imprinted onto TC4 titanium alloy using a micron-scale silicon imprinting template. The process is simple, low-cost, and highly efficient. Furthermore, the micron-scale structure replication accuracy is high, and the forming quality is excellent. Attached Figure Description

[0027] Figure 1 Morphological images of the microstructures obtained by hot pressing (60 kN, room temperature and 200 °C) on the surface of TC4 titanium alloy and crushed silicon templates are shown; wherein: (a) room temperature, (b) 200 °C, (c) crushed silicon templates (imprint depth on the surface of TC4 titanium alloy is 2-3 micrometers, and the height of the template microstructure is 15 micrometers);

[0028] Figure 2 This is a schematic diagram of a silicon substrate covered with a periodic square silica mask; the side length / spacing, i.e., a / b, is 2.5.

[0029] Figure 3 Scanning electron micrographs of pyramid-shaped silicon templates A and B obtained by wet etching are shown. For silicon template A: (a1) Low-magnification image of the pyramid microstructure; (a2) Magnified view of a part of the microstructure; (a3) ​​Partial cross-sectional view of the microstructure.

[0030] Silicon template B: (b1) Low-magnification topography of the pyramid microstructure; (b2) Enlarged view of a part of the microstructure; (b3) Partial cross-sectional view of the microstructure;

[0031] Figure 4 Display Figure 2 The image shows the morphology of the inverted pyramid microstructure formed by hot pressing (600°C, 60kN) on TC4 titanium alloy using silicon template A (Example 1);

[0032] Figure 5 Display Figure 2 The image shows the morphology of the inverted pyramid microstructure formed by hot pressing (700°C, 60kN) on TC4 titanium alloy using silicon template A (Example 2);

[0033] Figure 6 Display Figure 2 The image shows the morphology of the inverted pyramid microstructure formed by hot pressing (700°C, 60kN) on TC4 titanium alloy using silicon template B (Example 3). Detailed Implementation

[0034] The present invention will now be described in further detail with reference to specific embodiments.

[0035] This invention discloses a method for precisely fabricating inverted pyramid microstructures on high-hardness TC4 titanium alloy, comprising the following steps: firstly, a silicon imprint template is fabricated using photolithography, on which a microscale structure of an array of upright pyramids (first microstructure) is formed (first microstructure); then, the TC4 titanium alloy is hot-pressed at high temperature using the silicon imprint template to form an inverted pyramid array microscale structure (second microstructure) on the surface of the titanium alloy that is complementary to the microstructure on the silicon imprint template. The following three examples further illustrate this method.

[0036] Example 1:

[0037] S100: Fabricate a silicon imprint stencil, on the surface of which a first microstructure of a positive pyramid array is formed;

[0038] S200: The TC4 titanium alloy is hot-pressed using the silicon imprint template to form an inverted pyramid array second microstructure that is complementary to the first microstructure of the positive pyramid array on the silicon imprint template.

[0039] In Embodiment 1 of the present invention, step S100 employs photolithography and wet etching to process the mold, including the following steps: a) Photolithography to prepare a silicon dioxide mask: In this embodiment, the square periodic array mask pattern has a = 40 μm and b = 15 μm, as shown in the schematic diagram. Figure 2 As shown. Etching in BOE (49% HF: 40% NH4F = 1:6) for 3 min transfers the periodically arranged square photoresist pattern to the silicon dioxide layer. Then, the photoresist is dissolved in acetone for 7 min to obtain a silicon wafer covered with a square silicon dioxide mask.

[0040] b) Wet etching: The TMAH solution is heated to 85°C, and then the silicon wafer obtained in step a) is placed on a polytetrafluoroethylene basket and suspended in a 5% TMAH (tetramethylammonium hydroxide) solution. The wafer is etched for 45 min while being magnetically stirred at a speed of 60 r / min to obtain the wet-etched silicon wafer.

[0041] c) Removal of the silicon dioxide mask: Rinse the silicon wafer obtained in step b) with deionized water, then etch it in BOE solution for 5 minutes, and rinse it with deionized water again to obtain silicon imprint template A, the morphology of which is as follows. Figure 3 As shown in (a1-a3), the surface microstructure of silicon imprinting template A is uniform, the height of the single pyramid microstructure is small, and the top platform is wide.

[0042] In Embodiment 1 of the present invention, step S200 involves preparing an inverted pyramid array microstructure on the surface of TC4 titanium alloy using a hot pressing method, and includes the following steps:

[0043] a) Place the silicon template A with its microstructure onto the titanium alloy surface, then place the entire assembly in a hot press mold and smoothly into a hot press furnace. Close the hot press furnace and evacuate to a vacuum level of 3×10⁻⁶. -3 MPa;

[0044] b) The press applies a load of 10kN at a rate of 100N / s as a preload;

[0045] c) The sample is heated as a whole at a rate of 10°C / min and the heating temperature is set to 600°C.

[0046] d) After reaching the set temperature, load the TC4 titanium alloy with the silicon imprint template attached to the surface at a loading rate of 100 N / s and a set pressure of 60 kN, and hold the pressure for 120 seconds.

[0047] e) After the hot pressing process is completed, the pressure is unloaded, and the sample is cooled to room temperature in the furnace. The titanium alloy sample is then removed, and an inverted pyramid microstructure is obtained on its surface.

[0048] The morphology of the titanium alloy surface microstructure obtained according to steps S100 and S200 in Example 1 is as follows: Figure 4 As shown, under a temperature of 600℃ and a pressure of 60kN, the inverted pyramid microstructures obtained by hot pressing on the surface of the titanium alloy are relatively shallow (approximately 6μm) and have a wide spacing between adjacent inverted pyramid microcavity structures (approximately 15μm); the titanium alloy matrix does not deform.

[0049] Example 2:

[0050] Example 2 uses the same silicon imprinting template A as Example 1. The only difference in the hot pressing process of step S200 is that the hot pressing temperature is increased to 700°C. The microstructure morphology of the TC4 titanium alloy surface after hot pressing in Example 2 is as follows: Figure 5 Its surface inverted pyramid microstructure and morphology of silicon template A ( Figure 3 The a1-a3 microstructures are complementary, and the inverted pyramid microstructures on the surface of the titanium alloy are completely filled with a deeper depth (approximately 13 μm). The spacing between adjacent inverted pyramid microcavities is narrower (approximately 5 μm), but the titanium alloy matrix undergoes slight deformation.

[0051] Example 3:

[0052] The difference between Example 3 and Example 2 is the silicon imprint template and the solution concentration in step b) of step S100. A 4% TMAH solution (tetramethylammonium hydroxide) is selected, and the etching time is 35 min. The morphology of the resulting silicon imprint template B is as follows. Figure 3As shown in (b1-b3), the surface microstructure of the silicon imprinting template B is uniform, the width of the top platform is reduced, and the height of the single pyramid microstructure is increased. In step S200, the hot-pressing temperature is 700°C and the pressure is 60kN. The surface microstructure of the TC4 titanium alloy after hot pressing is as follows: Figure 6 As shown, the inverted pyramid microstructure on its surface is complementary to the microstructure of silicon template B. The inverted pyramid microstructure on the surface of the titanium alloy is completely filled and has a deeper depth (approximately 20 μm). The spacing between adjacent inverted pyramid microcavity structures is narrower (approximately 5 μm), but the titanium alloy matrix undergoes slight deformation.

[0053] In this invention, a silicon template is prepared by photolithography, which effectively transforms a silicon substrate covered with a periodic silicon dioxide mask into a regular, ordered, highly repeatable, and dimensionally accurate micron-scale pyramidal array silicon substrate. This silicon template is reusable, and its pyramidal microstructure can be customized in different sizes and morphologies by adjusting the solubility of the etching solution. In this invention, the high-temperature hot pressing process effectively softens the titanium alloy, reducing its yield strength during molding, enabling microimprinting, and improving the accuracy of the microimprinting. The micron-scale inverted pyramidal structure prepared on the surface of TC4 titanium alloy by combining the high-temperature hot pressing process with a micron-scale silicon imprinting template exhibits resistance to external friction. Furthermore, the high-temperature hot pressing process is simple, low-cost, efficient, and provides good formability.

[0054] The method of the present invention allows for the selection of process parameters in different embodiments based on the different requirements of the micron structure on the surface of titanium alloys in practical applications, thereby achieving low-cost preparation of wear-resistant micron structures on the surface of titanium alloys.

[0055] This invention addresses the current situation where microimprinting technology can only successfully fabricate micron-sized structures on soft metals (such as aluminum, magnesium, and copper alloys with a hardness of 60-100 HV). It effectively solves the problem of difficulty in imprinting micron-sized structures on titanium alloys (with a hardness of 300-400 HV), which have a much higher hardness than metals such as aluminum alloys.

[0056] As described above, the present invention can be implemented well.

[0057] The implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for precisely fabricating microstructures on the surface of high-hardness TC4 titanium alloy, characterized in that... Includes the following steps: S100: Fabricate a silicon imprint stencil, on the surface of which a first microstructure of a positive pyramid array is formed; S200: TC4 titanium alloy is hot-pressed at high temperature using a silicon imprinting template to form a second inverted pyramid array microstructure on the surface of the titanium alloy that is complementary to the first microstructure of the positive pyramid array of the silicon imprinting template. In step S100, the silicon imprint template is processed using photolithography and wet etching, specifically including the following steps: 101) Photolithography to prepare silicon dioxide mask: A pre-designed pattern is prepared on the surface of a silicon wafer with an oxide layer by photolithography. The pattern is a square periodic array. Etching with BOE at a ratio of 49%HF:40%NH4F = 1:6 for 3 minutes transfers the periodically arranged square photoresist pattern to the silicon dioxide layer. Then, the photoresist is dissolved with acetone for 7 minutes, so that the corrosion-resistant silicon dioxide layer can serve as the actual mask, resulting in a silicon wafer covered with a square silicon dioxide mask. 102) Wet etching: Heat the TMAH solution to 85°C, place the silicon wafer covered with a square silicon dioxide mask on a polytetrafluoroethylene basket and suspend it in a 4%~5% TMAH solution, and etch for 35min~45min to obtain a silicon wafer with a positive pyramid array microstructure covered with a silicon dioxide mask. 103) Removal of silicon dioxide mask: Take the polytetrafluoroethylene basket containing the etched silicon wafer out of the TMAH solution, rinse with deionized water, then place it in BOE solution for 5 minutes for etching, and then rinse with deionized water to obtain a silicon imprint template with a positive pyramid micron structure. In step S200, the high-temperature hot pressing specifically includes the following steps: 201) Sample Placement: Place the silicon imprint template with the microstructure onto the titanium alloy surface, then place the entire template into the hot imprint mold, and carefully place it into the hot press furnace. Close the hot press furnace and evacuate for 3×10⁻⁶ seconds. -3 MPa; 202) Preloading process: The press loads 10kN at a rate of 100N / s as a preloading load to reduce the thermal rebound effect on the sample surface during hot pressing. 203) Heating process: The sample is heated as a whole by the heating system of the press. The heating temperature is set to 600~700℃ and the heating rate is 10℃ / min. The sample is heated slowly to make it heat evenly and reduce the temperature difference between the sample and the set temperature. 204) Hot pressing process: After reaching the set temperature, the TC4 titanium alloy with silicon imprint template attached to the surface is loaded by the pressure system of the press machine. The loading rate is 100 N / s, the set pressure is 60 kN, and the pressure is held for 120 s under the set pressure. The pressure is slowly increased to make the sample hot pressing uniform, and the heat rebound effect in hot pressing is reduced by holding the pressure. 205) Sample removal: After the hot pressing process is completed, the pressure is unloaded, and the sample is cooled to room temperature with the furnace. The titanium alloy sample is then removed, and its surface has an inverted pyramid microstructure.

2. The method for precisely fabricating microstructures on the surface of high-hardness TC4 titanium alloy according to claim 1, characterized in that: Step 101) The ratio of the side length to the spacing of the silicon dioxide square mask is 2.

5.

3. The method for precisely fabricating microstructures on the surface of high-hardness TC4 titanium alloy according to claim 1, characterized in that: Step 102) During the wet etching process, magnetic stirring is applied at a speed of 60 r / min.

4. A periodically arrayed inverted pyramid microstructure, characterized in that... Obtained by the method described in any one of claims 1-3.

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