A method for preparing a gradient W-Ta alloy nanofilm

Abstract

The application discloses a method for preparing a gradient W-Ta alloy nanometer film, and comprises the following steps: firstly, cleaning W target material, Ta target material and a single crystal Si substrate; secondly, installing the cleaned W target material, the Ta target material and the single crystal Si substrate in a cavity of a magnetron sputtering device to obtain an assembled magnetron sputtering device; thirdly, vacuumizing the cavity of the assembled magnetron sputtering device; fourthly, pre-sputtering each target material; and fifthly, sputtering to obtain the gradient WTa alloy nanometer film. By controlling the installation power position of the target material and the Ta target material and the process parameters of a direct current power source and a radio frequency power source in the sputtering process, a hard base layer, an intermediate layer and a soft surface layer are sequentially deposited on the base to obtain the gradient WTa alloy nanometer film with a tough surface and a hard core, the room temperature plastic deformation capacity of the WTa alloy is improved under the premise of ensuring the strength, and the method is efficient, convenient and highly controllable.

Description

Technical Field

[0001] This invention belongs to the field of tungsten alloy microstructure design technology, specifically relating to a method for preparing gradient W-Ta alloy nanofilms. Background Technology

[0002] With the increasing demands on structural materials for service life, high-melting-point materials have become a research hotspot in recent years. W, as the metallic material with the highest melting point (3380℃) discovered to date, has attracted widespread attention for its mechanical properties and irradiation performance. Similar to most refractory metals, the W system has a body-centered cubic crystal structure, and its ductile-brittle transition temperature is significantly higher than room temperature, thus exhibiting almost zero elongation at room temperature.

[0003] The main methods for preparing W-Ta alloys include powder metallurgy and vacuum melting. Based on these methods, the alloy is subjected to hot pressure processing with a certain amount of deformation to obtain a W-Ta alloy with a uniform microstructure and fine grains. However, this preparation method has disadvantages such as high processing cost and high processing difficulty. Furthermore, W alloys exhibit very poor low-temperature plastic deformation capacity, which makes W and W alloys extremely prone to cracking during processing. Therefore, the methods for improving plastic deformation capacity are very limited. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing gradient W-Ta alloy nanofilms. This method, by controlling the mounting positions of the target and Ta target, and controlling the process parameters of the DC and RF power supplies during sputtering, sequentially deposits a hard substrate layer, an intermediate layer, and a soft surface layer on a substrate to obtain a surface-tough, core-hard gradient WTa alloy nanofilm. While ensuring strength, this method improves the room-temperature plastic deformation capability of the WTa alloy, solving the problem of the difficulty in improving the plastic deformation capability of W-Ta alloys.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing gradient W-Ta alloy nanofilms, characterized in that the method includes the following steps:

[0006] Step 1: Clean the W target, Ta target, and single-crystal Si substrate;

[0007] Step 2: Install the cleaned W target, Ta target and single crystal Si substrate from Step 1 into the cavity of the magnetron sputtering equipment. The cleaned W target is installed at one end of the DC power supply of the magnetron sputtering equipment, the cleaned Ta target is installed at one end of the RF power supply of the magnetron sputtering equipment, and the cleaned single crystal Si substrate is installed at the sputtering stage position to obtain the assembled magnetron sputtering equipment.

[0008] Step 3: Evacuate the cavity of the assembled magnetron sputtering equipment obtained in Step 2 to obtain the vacuum-evacuated magnetron sputtering equipment.

[0009] Step 4: Turn on the DC power supply and RF power supply of the vacuum magnetron sputtering equipment obtained in Step 3, and pre-sputter each target material to obtain a vacuum magnetron sputtering equipment with pre-sputtered targets.

[0010] Step 5: Turn on the DC power supply and RF power supply of the vacuum magnetron sputtering equipment with pre-sputtered targets obtained in Step 4, and use the pre-sputtered targets to sputter the single-crystal Si substrate to obtain a gradient WTa alloy nanofilm on the surface of the single-crystal Si substrate.

[0011] During the research process of this invention, the effect of Ta content in nanocrystalline W-Ta alloy on the strength and plasticity of the alloy was studied. The results showed that even when nanocrystals form a supersaturated solid solution, W-Ta alloy with high Ta content (greater than 40 at.%) still has good strength and plastic deformation ability.

[0012] In the preparation process of this invention, impurities on the surfaces of the W target, Ta target and single-crystal Si substrate are removed by cleaning. Vacuuming is performed inside the cavity of the assembled magnetron sputtering equipment to remove other gases inside the cavity and prevent the introduction of impurities. The surface oxide layer is removed by pre-sputtering each target, thereby ensuring the quality of the gradient WTa alloy nanofilm.

[0013] Since the sputtering rate of DC power supply is higher than that of RF power supply, this invention obtains a higher W deposition rate by mounting the W target at one end of the DC power supply of the magnetron sputtering equipment, and reduces the Ta deposition rate by mounting the Ta target at one end of the RF power supply of the magnetron sputtering equipment, so as to precisely control the composition of each layer of the gradient W-Ta alloy nanofilm.

[0014] The method for preparing gradient W-Ta alloy nanofilms described above is characterized in that the W target material in step one has a mass purity of 99.98% or higher, and the Ta target material has a mass purity of 99.97% or higher.

[0015] The method for preparing gradient W-Ta alloy nanofilms described above is characterized in that the orientation of the single-crystal Si substrate in step one is

[111] . Since nanocrystalline BCC crystals are mostly grown with a

[111] orientation, selecting a

[111] oriented single-crystal Si substrate greatly reduces growth stress and improves the film-substrate bonding strength.

[0016] The method for preparing gradient W-Ta alloy nanofilms described above is characterized in that the cleaning process in step one involves sequentially ultrasonically vibrating the film in acetone, anhydrous ethanol, and deionized water for at least 10 minutes each, followed by drying. This invention effectively removes surface impurities through ultrasonic vibration in a medium.

[0017] The method for preparing gradient W-Ta alloy nanofilms described above is characterized in that the vacuum level inside the cavity of the vacuum magnetron sputtering equipment in step three is no greater than 3.0 × 10⁻⁶. -4 Pa.

[0018] The method for preparing gradient W-Ta alloy nanofilms described above is characterized in that, in step four, the power of both the DC power supply and the RF power supply during the pre-sputtering process is 155W to 165W, and the pre-sputtering time is 15 minutes. By controlling the power supply during the pre-sputtering process, high-energy ion bombardment is achieved on the target surface, thereby effectively cleaning the target surface.

[0019] The method for preparing gradient W-Ta alloy nanofilms described above is characterized in that, in step five, during the sputtering process, the power of the DC power supply is turned on and adjusted to 155W-165W, the RF power supply is turned off and sputtering deposition is performed for 30 minutes to form a hard substrate layer on a single-crystal Si substrate. Then, the power of the RF power supply is increased to 85W-95W and sputtering deposition is continued for 10 minutes to form an intermediate layer on the substrate layer. Then, the power of the RF power supply is increased to 155W-165W and sputtering deposition is continued for 20 minutes to form a soft surface layer on the intermediate layer, thereby obtaining a gradient W-Ta alloy nanofilm.

[0020] In this invention, the power of the DC power supply is set to 155W to 165W during the sputtering process. This power is relatively stable and the sputtering rate is moderate. At the same time, by stepwise adjusting the power of the RF power supply and controlling the sputtering deposition time of each stage, a base layer, an intermediate layer and a surface layer with a gradient distribution of Ta composition are deposited sequentially on a single-crystal Si substrate. Under the premise of ensuring a high deposition rate, a high-density gradient W-Ta alloy nanofilm is obtained.

[0021] The method for preparing gradient W-Ta alloy nanofilms described above is characterized in that, in step five, the substrate layer is a W film, the intermediate layer is a W-15Ta alloy, and the soft surface layer is a W-45Ta alloy.

[0022] The method for preparing gradient W-Ta alloy nanofilms described above is characterized by using a nanoindenter to test the hardness of the gradient W-Ta nanofilm obtained in step five. The test mode is the continuous stiffness method, the indentation depth is 200 nm, and the strain rate is 0.05 s⁻¹. -1Furthermore, the average value of ten points tested for each sample is taken as the hardness value. The testing mode of this invention can obtain a curve showing the continuous change of hardness with indentation depth, thereby obtaining more comprehensive hardness data; the selected indentation depth is usually less than 1 / 10 of the test sample, effectively avoiding the influence of the substrate on the test results; the selected strain rate is relatively moderate, and the test stability is high.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. This invention applies the design concept of gradient materials to the W alloy system. By controlling the mounting power positions of the W and Ta targets and the process parameters of the DC and RF power supplies during sputtering, a W thin film with high strength but extremely poor plasticity is first deposited as the first hard substrate. Then, a W-15Ta alloy with moderate strength and plasticity is deposited on the hard substrate as the second intermediate layer. Finally, a W-45Ta alloy with low strength but high plasticity is deposited on the intermediate layer as the third soft surface layer, resulting in a gradient W-Ta alloy nanofilm with tough surface and hard core. This film has a nanoscale grain size, thereby improving the room temperature plastic deformation capability of the W-Ta alloy while ensuring strength.

[0025] 2. This invention applies the preparation method of nano-multilayer films to the gradient W-Ta alloy system, thereby improving the strength and deformation coordination ability of gradient W-Ta alloy nanofilms.

[0026] 3. This invention uses physical vapor deposition, i.e., magnetron sputtering, to obtain gradient W-Ta alloy nanofilms based on reasonable design of composition and process parameters. This method is efficient, convenient, and highly controllable.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] Figure 1 This is a cross-sectional SEM image of the gradient W-Ta alloy nanofilm prepared in Example 1 of the present invention.

[0029] Figure 2 The image shows the surface SEM morphology of the gradient W-Ta alloy nanofilm prepared in Example 1 of this invention.

[0030] Figure 3 This is an energy dispersive spectral scan of the gradient W-Ta alloy nanofilm prepared in Example 1 of the present invention.

[0031] Figure 4 The image shows the X-ray diffraction pattern of the gradient W-Ta alloy nanofilm prepared in Example 1 of this invention.

[0032] Figure 5This is a low-magnification TEM transmission electron microscope image of the gradient W-Ta alloy nanofilm prepared in Example 1 of the present invention.

[0033] Figure 6 This is a TEM line scan energy spectrum of the gradient W-Ta alloy nanofilm prepared in Example 1 of the present invention.

[0034] Figure 7 This is a cross-sectional SEM image of the W-15Ta alloy nanofilm prepared in Comparative Example 1 of this invention.

[0035] Figure 8 The image shows the surface SEM morphology of the W-15Ta alloy nanofilm prepared in Comparative Example 1 of this invention.

[0036] Figure 9 This is an energy dispersive spectroscopy (EDS) spot scan of the W-15Ta alloy nanofilm prepared in Comparative Example 1 of this invention.

[0037] Figure 10 The image shows the X-ray diffraction pattern of the W-15Ta alloy nanofilm prepared in Comparative Example 1 of this invention.

[0038] Figure 11 This is a cross-sectional SEM image of the W-45Ta alloy nanofilm prepared in Comparative Example 2 of this invention.

[0039] Figure 12 The image shows the surface SEM morphology of the W-45Ta alloy nanofilm prepared in Comparative Example 2 of this invention.

[0040] Figure 13 This is an energy dispersive spectroscopy (EDS) spot scan of the W-45Ta alloy nanofilm prepared in Comparative Example 2 of this invention.

[0041] Figure 14 The image shows the X-ray diffraction pattern of the W-45Ta alloy nanofilm prepared in Comparative Example 2 of this invention.

[0042] Figure 15 This is a cross-sectional SEM image of the W nanofilm prepared in Comparative Example 3 of this invention.

[0043] Figure 16 The image shows the surface SEM morphology of the W nanofilm prepared in Comparative Example 3 of this invention.

[0044] Figure 17 This is an energy dispersive spectral scan of the W nanofilm prepared in Comparative Example 3 of this invention.

[0045] Figure 18 The image shows the X-ray diffraction pattern of the W nanofilm prepared in Comparative Example 3 of this invention.

[0046] Figure 19The load-displacement curves of the films prepared in Example 1 and Comparative Examples 1 to 3 of the present invention during the pressing process are shown.

[0047] Figure 20 The graphs show the change in hardness of the films prepared in Example 1 and Comparative Examples 1-3 of this invention as a function of indentation depth. Detailed Implementation

[0048] Example 1

[0049] This embodiment includes the following steps:

[0050] Step 1: Clean the W target, Ta target and single crystal Si substrate to remove surface impurities; the mass purity of the W target is 99.98%, the mass purity of the Ta target is 99.97%, and the orientation of the single crystal Si substrate is

[111] ; the cleaning process is as follows: ultrasonically vibrate for 10 minutes in acetone, anhydrous ethanol and deionized water respectively, and finally dry with a hair dryer;

[0051] Step 2: Install the W target material from Step 1 at one end of the DC power supply of the magnetron sputtering equipment, install the cleaned Ta target material at one end of the RF power supply of the magnetron sputtering equipment, and install the cleaned single-crystal Si substrate at the sputtering stage position to obtain the assembled magnetron sputtering equipment.

[0052] Step 3: Using a two-stage vacuum system consisting of a mechanical pump and a molecular pump, evacuate the cavity of the assembled magnetron sputtering equipment obtained in Step 2 to a vacuum level not exceeding 3.0 × 10⁻⁶. -4 Pa, to obtain a vacuum magnetron sputtering device;

[0053] Step 4: Turn on the DC power supply and RF power supply of the vacuum magnetron sputtering equipment obtained in Step 3, and perform pre-sputtering on each target to remove the surface oxide layer, thereby obtaining a vacuum magnetron sputtering equipment with pre-sputtered targets; the power of the DC power supply and RF power supply during the pre-sputtering process is 155W~165W, and the pre-sputtering time is 15min.

[0054] Step 5: Re-enable the DC and RF power supplies of the vacuum magnetron sputtering equipment with the pre-sputtered substrate obtained in Step 4, and sputter the pre-sputtered single-crystal Si substrate. During the sputtering process, first set the DC power supply to 155W-165W and turn off the RF power supply for sputtering deposition for 30 minutes to form a W thin film hard substrate on the single-crystal Si substrate. Then turn on the RF power supply and set the RF power supply to 85W-95W, and continue to maintain the DC power supply at 155W-165W for sputtering deposition for 10 minutes to form a W-15Ta alloy intermediate layer on the W thin film. Then set the RF power supply to 155W-165W and continue to maintain the DC power supply at 155W-165W for sputtering deposition for 20 minutes to form a W-45Ta alloy soft surface layer on the W-15Ta alloy intermediate layer, thus obtaining a gradient WTa alloy nanofilm.

[0055] Figure 1 This is a cross-sectional SEM image of the gradient W-Ta alloy nanofilm prepared in this embodiment. Figure 1 It can be seen that the total thickness of the gradient W-Ta alloy nanofilm is 3.8 μm. There is a region with a thickness of about 0.6 μm composed of fine grains near the single crystal Si substrate. Above this region, the grains grow in the form of columnar crystals up to the surface of the film.

[0056] Figure 2 Here are the surface SEM images of the gradient W-Ta alloy nanofilms prepared in this embodiment, from... Figure 2 It can be seen that the surface of this gradient W-Ta alloy nanofilm exhibits a circular cluster structure, consistent with... Figure 1 The columnar crystal morphology corresponds to that in the text.

[0057] Figure 3 This is an energy dispersive spectral pattern of the gradient W-Ta alloy nanofilm prepared in this embodiment. Figure 3 It can be seen that the test results of three randomly selected locations in the gradient W-Ta alloy nanofilm show that the average Ta atom content is 30%.

[0058] Figure 4 This is the X-ray diffraction pattern of the gradient W-Ta alloy nanofilm prepared in this embodiment. Figure 4 The peak value of 2θ in the middle represents the five typical α-W crystal planes from left to right: 110, 200, 211, 220 and 310, indicating that the gradient W-Ta alloy nanofilm prepared in this embodiment is an α-W single-phase solid solution.

[0059] Figure 5 This is a low-magnification TEM transmission electron microscope image of the gradient W-Ta alloy nanofilm prepared in this embodiment. Figure 5It can be seen that the bottom layer and the darkest layer in the gradient W-Ta alloy nanofilm is the first deposited W film, the middle layer is the second deposited W-15Ta alloy film, which is thinner and lighter in color, and the top layer and the lightest in color is the third deposited W-45Ta alloy film.

[0060] Figure 6 The image shows the TEM line scan energy spectrum of the gradient W-Ta alloy nanofilm prepared in this embodiment. Figure 6 It can be seen that in the gradient W-Ta alloy nanofilm, the atomic ratio of Ta in the darkest layer on the right is about 15%, and the thickness of this layer is about 1.5 μm; while in the lightest layer on the left, the atomic ratio of Ta is about 45%, and the thickness of this layer is about 2 μm.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that in step five, the power of the DC power supply is set to 155W-165W and the power of the RF power supply is set to 85W-95W for sputtering for 1 hour to obtain W-15Ta alloy nanofilm.

[0063] Figure 7 This is a cross-sectional SEM image of the W-15Ta alloy nanofilm prepared in this comparative example. Figure 7 It can be seen that, with Figure 1 Unlike other materials, the grain morphology of the W-15Ta alloy nanofilm near the substrate is not significantly different from that near the surface.

[0064] Figure 8 Here are the surface SEM images of the W-15Ta alloy nanofilm prepared in this comparative example. Figure 8 It can be seen that, with Figure 2 Similarly, the W-15Ta alloy nanofilm grew in a columnar crystal manner, and the grain size did not change significantly.

[0065] Figure 9 This is the energy dispersive spectroscopy (EDS) spot scan of the W-15Ta alloy nanofilm prepared in this comparative example. Figure 9 It can be seen that the atomic ratio of Ta in this W-15Ta alloy nanofilm is about 15%.

[0066] Figure 10 The X-ray diffraction pattern of the W-15Ta alloy nanofilm prepared in this comparative example is shown below. Figure 10 It can be seen that, with Figure 4 Similarly, the W-15Ta alloy nanofilm is an α-W solid solution.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that in step five, the power of the DC power supply is set to 155W-165W and the power of the RF power supply is set to 155W-165W for sputtering for 1 hour to obtain W-45Ta alloy nanofilm.

[0069] Figure 11 This is a cross-sectional SEM image of the W-45Ta alloy nanofilm prepared in this comparative example. Figure 11 It can be seen that the thickness of the W-45Ta alloy nanofilm is approximately 2.7 μm.

[0070] Figure 12 The above are SEM images of the surface morphology of the W-45Ta alloy nanofilm prepared in this comparative example. Figure 12 It can be seen that the surface of this W-45Ta alloy nanofilm is... Figure 8 Similar to.

[0071] Figure 13 This is the energy dispersive spectroscopy (EDS) spot scan of the W-45Ta alloy nanofilm prepared in this comparative example. Figure 13 It can be seen that the atomic ratio of Ta in this W-45Ta alloy nanofilm is about 45%.

[0072] Figure 14 The X-ray diffraction pattern of the W-45Ta alloy nanofilm prepared in this comparative example is shown below. Figure 14 It can be seen that the structure of the W-45Ta alloy nanofilm is the same as that of the nanofilms prepared in Example 1 and Comparative Example 2.

[0073] Comparative Example 3

[0074] The difference between this comparative example and Example 1 is that in step five, only the DC power supply is turned on and the power of the DC power supply is set to 155W~165W for sputtering for 1 hour.

[0075] Figure 15 This is a cross-sectional SEM image of the W nanofilm prepared in this comparative example. Figure 15 The phenomenon of localized breakage and detachment of the W nanofilm can be clearly observed, indicating that the W nanofilm is very brittle at room temperature.

[0076] Figure 16 Here are the surface SEM images of the W nanofilms prepared in this comparative example. Figure 16 It can be seen that, compared to Figure 3 The gradient W-Ta alloy nanofilm of Example 1 has a slightly larger columnar crystal cluster size.

[0077] Figure 17 This is the energy dispersive spectral pattern of the W nanofilm prepared in this comparative example. Figure 17It can be seen that the W nanofilm is a pure W film.

[0078] Figure 18 The X-ray diffraction pattern of the W nanofilm prepared in this comparative example is shown below. Figure 18 It can be seen that this W nanofilm is related to Figure 4 Similar to the gradient W-Ta alloy nanofilm of Example 1.

[0079] Figure 19 This is a load-displacement curve diagram of the films prepared in Example 1 and Comparative Examples 1-3 of the present invention during the pressing process. Figure 19 It can be seen that as the indentation depth increases, the load of the W nanofilm is always higher than that of the W-Ta alloy nanofilm; at the same time, in the W-Ta alloy, the load value of the gradient W-Ta alloy nanofilm in Example 1 is significantly higher than that of the homogeneous W-15Ta alloy nanofilm in Comparative Example 1 and the W-45Ta alloy nanofilm in Comparative Example 2.

[0080] The films prepared in Example 1 and Comparative Examples 1-3 of this invention were subjected to hardness testing using a nanoindenter. The testing mode was the continuous stiffness method, the indentation depth was 200 nm, and the strain rate was 0.05 s⁻¹. -1 Furthermore, the hardness value was obtained by averaging ten points tested on each sample, and the results are as follows: Figure 20 As shown.

[0081] Figure 20 This is a graph showing the change in hardness of the films prepared in Example 1 and Comparative Examples 1-3 of the present invention as a function of indentation depth. Figure 20 It can be seen that, with Figure 19 The trend is similar. During the pressing process, the hardness of the W nanofilm is moderate and at its highest point. The hardness value of the gradient W-Ta alloy nanofilm in Example 1 is second only to W, and much higher than that of the homogeneous W-15Ta alloy nanofilm in Comparative Example 1 and the W-45Ta alloy nanofilm in Comparative Example 2.

[0082] In summary, by comparing Example 1 of the present invention with Comparative Examples 1 to 3, it can be seen that the present invention obtains a gradient W-Ta alloy nanofilm with excellent comprehensive mechanical properties by controlling the composition and structure of the gradient W-Ta alloy nanofilm.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing gradient W-Ta alloy nanofilms, characterized in that, The method includes the following steps: Step 1: Clean the W target, Ta target, and single-crystal Si substrate; Step 2: Install the cleaned W target, Ta target and single crystal Si substrate from Step 1 into the cavity of the magnetron sputtering equipment. The cleaned W target is installed at one end of the DC power supply of the magnetron sputtering equipment, the cleaned Ta target is installed at one end of the RF power supply of the magnetron sputtering equipment, and the cleaned single crystal Si substrate is installed at the sputtering stage position to obtain the assembled magnetron sputtering equipment. Step 3: Evacuate the cavity of the assembled magnetron sputtering equipment obtained in Step 2 to obtain the vacuum-evacuated magnetron sputtering equipment. Step 4: Turn on the DC power supply and RF power supply of the vacuum magnetron sputtering equipment obtained in Step 3, and pre-sputter each target material to obtain a vacuum magnetron sputtering equipment with pre-sputtered targets. Step 5: Re-enable the DC power supply and RF power supply of the vacuum magnetron sputtering equipment with pre-sputtered targets obtained in Step 4. Use the pre-sputtered targets to sputter the single-crystal Si substrate to obtain a gradient WTa alloy nanofilm on the surface of the single-crystal Si substrate. During the sputtering process, turn on and adjust the power of the DC power supply to 155W~165W, turn off the RF power supply and perform sputtering deposition for 30 minutes to form a hard substrate layer on the single-crystal Si substrate. Then increase the power of the RF power supply to 85W~95W and continue sputtering deposition for 10 minutes to form an intermediate layer on the substrate layer. Then increase the power of the RF power supply to 155W~165W and continue sputtering deposition for 20 minutes to form a soft surface layer on the intermediate layer, thus obtaining a gradient W-Ta alloy nanofilm.

2. The method for preparing gradient W-Ta alloy nanofilms according to claim 1, characterized in that, The W target material mentioned in step one has a purity of 99.98% or higher, and the Ta target material has a purity of 99.97% or higher.

3. The method for preparing gradient W-Ta alloy nanofilms according to claim 1, characterized in that, The orientation of the single-crystal Si substrate mentioned in step one is [111].

4. The method for preparing gradient W-Ta alloy nanofilms according to claim 1, characterized in that, The cleaning process described in step one is as follows: ultrasonically vibrate in acetone, anhydrous ethanol and deionized water for more than 10 minutes each, and finally blow dry.

5. The method for preparing gradient W-Ta alloy nanofilms according to claim 1, characterized in that, The vacuum level inside the cavity of the vacuum magnetron sputtering equipment described in step three shall not exceed 3.0 × 10⁻⁶. -4 Pa.

6. The method for preparing gradient W-Ta alloy nanofilms according to claim 1, characterized in that, In step four, the power of both the DC power supply and the RF power supply during the pre-sputtering process is 155W~165W, and the pre-sputtering time is 15min.

7. The method for preparing gradient W-Ta alloy nanofilms according to claim 1, characterized in that, The substrate layer described in step five is a W thin film, the intermediate layer is a W-15Ta alloy, and the soft surface layer is a W-45Ta alloy.

8. The method for preparing gradient W-Ta alloy nanofilms according to claim 1, characterized in that, The hardness of the gradient W-Ta nanofilm described in step five was tested using a nanoindenter. The test mode was the continuous stiffness method, the indentation depth was 200 nm, and the strain rate was 0.05 s⁻¹. -1 Furthermore, the average value of ten points tested for each sample is taken as the hardness value.

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