Current-direction-controllable electrically-assisted three-point bending test device and method

Abstract

The invention belongs to the technical field of material mechanical property measurement, and particularly discloses a current-direction-controllable electrically-assisted three-point bending test device which comprises a female die, a male die and a clamping part for arranging an electrode on a to-be-tested sample, and a groove for placing the to-be-tested sample is formed in the female die. According to the electrically-assisted three-point bending test device, the current direction can be accurately regulated and controlled in real time through the female die, the male die and the clamping part capable of arranging the electrode on the to-be-tested sample, the electrically-assisted three-point bending test device is suitable for regulating the current direction under different loading paths, and deformation of the to-be-tested sample can be observed in situ.

Description

Technical Field

[0001] This invention belongs to the field of material mechanical property measurement technology, specifically relating to an electrically assisted three-point bending test device and method with controllable current direction. Background Technology

[0002] Electro-assisted forming technology for lightweight, high-strength metallic materials introduces an electric current into the metal material, causing deformation and yielding the desired component. It reduces flow stress, delays necking, improves fatigue life, and obtains materials with high formability limits and microstructure quality through electrothermal and non-thermal effects. The electrothermal effect is based on the heat energy generated by the current flowing through the material and its resistance; Joule heating is the core physical basis of electro-assisted forming technology. Non-thermal effects include electron wind or electromagnetic force. Both electrothermal and non-thermal effects act on the forming process, reducing the material's yield strength, influencing dislocation movement and grain boundary behavior, and promoting dynamic recrystallization and defect repair.

[0003] The three-point bending test simulates the stress state of a component, measures its deformation behavior under bending load, and obtains information such as strength and stiffness under specific loads. It has advantages such as simple loading method, significant stress concentration, and easy evaluation of the stress intensity factor at the crack tip. It is suitable for analyzing bending failure behavior and the crack propagation and fatigue performance evolution of notched materials, and is a primary means of optimizing the process of conductive-assisted forming of lightweight, high-strength metallic materials such as titanium alloys. Based on the influence of current on the internal energy field distribution of materials, a current-assisted three-point bending test platform is constructed to examine the effect of current on the electroplastic behavior of materials. This is one of the main ways to reveal the electro-thermal-mechanical multi-field coupling mechanism and broaden the industrial application of electro-assisted forming.

[0004] In the process of realizing this invention, the inventors discovered at least the following problems in the prior art: Existing current-assisted three-point bending test devices often fix the positive and negative terminals of the power supply to the fatigue specimen device. For example, patent application document 202310108483.6 discloses a bidirectional loading current-assisted three-point bending test device, which achieves the bending test by clamping the positive and negative terminals of the power supply onto two support rods respectively to apply the bending load with electrical assistance. This device has the defect of affecting the acquisition of deformation information and cannot acquire information on the deformation performance of materials in different current directions. The current direction is a key variable that determines the internal energy field distribution of a material. Its change directly affects the local temperature gradient, stress distribution, and microstructure evolution characteristics of the material, leading to significant differences in macroscopic mechanical properties such as flow stress, crack initiation location, plasticity, and fatigue behavior. Current methods for improving the aforementioned electrically assisted three-point bending test apparatus to achieve controllable current direction, such as introducing rotatable electrodes, pluggable electrodes, or electrode adjustment structures driven by motors, often suffer from problems such as large structural volume, cumbersome adjustment steps, and inability to achieve precise and rapid adjustment of the current direction. Furthermore, these improved devices still have drawbacks, such as obstructing the test sample, affecting in-situ observation, and even causing current leakage that affects the load. Providing an electrically assisted three-point bending test with controllable current direction, which can accurately obtain multi-dimensional data on the electroplastic behavior of materials, is key to improving the optimization of auxiliary forming parameters in electrically assisted three-point bending tests. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an electrically assisted three-point bending test device and method with controllable current direction, in order to address the shortcomings of the prior art.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] On the one hand, an electrically assisted three-point bending test device with controllable current direction is provided, including a concave mold, a convex mold, and a clamping component for placing electrodes on the test sample. The concave mold has a groove for placing the test sample.

[0008] On the other hand, a method for using the above-mentioned electrically assisted three-point bending test device with controllable current direction is provided, comprising: inserting electrodes into a clamping component; clamping the clamping component containing the electrodes onto the test sample, placing it in the groove of the concave mold, and adjusting the convex mold to face the test sample.

[0009] Compared with the prior art, the present invention has the following advantages:

[0010] 1. The present invention provides an electrically assisted three-point bending test device with controllable current direction. Through a concave die, a convex die, and a clamping component for placing electrodes on the test sample, the current direction can be controlled in real time and precisely. It is suitable for adjusting the current direction under different loading paths and allows for in-situ observation of the deformation of the test sample.

[0011] 2. The electric-assisted three-point bending test device with controllable current direction of the present invention includes a clamping component composed of an insulated first buckle and a second buckle, which can realize that the current only passes through the inside of the test sample, and there is no current leakage during the test, which can ensure the accuracy of the test and has the characteristics of high repeatability.

[0012] 3. The electric-assisted three-point bending test device with controllable current direction of the present invention realizes the placement of the optical lens through the slot opened on the concave mold. During the test, it can ensure that the optical lens and the test sample remain perpendicular and unobstructed, and the current input and optical observation do not interfere with each other.

[0013] 4. The electrically assisted three-point bending test device with controllable current direction of the present invention can be directly installed on the fatigue testing machine. It is convenient to operate, highly durable, and suitable for in-situ observation experiments of various complex mechanical properties such as fatigue crack propagation.

[0014] 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

[0015] Figure 1 This is a schematic diagram of the installation of the test apparatus in Example 1;

[0016] Figure 2 This is a schematic diagram showing the connection relationship between the clamping component and the test sample in Example 1;

[0017] Figure 3 This is a schematic diagram of the clamping component in Example 1;

[0018] Figure 4 Optical photographs showing the test apparatus of the present invention mounted on a fatigue testing machine.

[0019] Explanation of reference numerals in the attached figures

[0020] 1—Punch; 2—Supporting rod; 3—Test sample;

[0021] 4—Die; 501—Plate-shaped part; 502—Snap-fit ​​part;

[0022] 6—Electrode. Detailed Implementation

[0023] The technical solution will now be clearly and completely described with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0024] In the following description, the term "and / or" is used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural.

[0025] In the following description, the terms “including,” “containing,” “having,” and “containing” are open-ended terms, meaning that they include but are not limited to.

[0026] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0027] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] The technical principle adopted in this invention is based on a clamping component set on the test sample, which cooperates with the concave and convex molds to achieve precise adjustment of the current direction within the test sample within the range of 0 to 45°.

[0030] In this invention, the "current direction" is defined as the angle between the line connecting the centers of the two electrodes and the horizontal axis of the sample.

[0031] A current-direction controllable electrically assisted three-point bending test device includes a concave mold 4, a convex mold 1, and a clamping component for placing an electrode 6 on a test sample 3. The concave mold 4 has a groove for placing the test sample 3.

[0032] This invention creatively proposes a three-point bending test device based on controllable current direction. Through the clamping component set on the test sample, the current direction can be precisely adjusted within the range of 0 to 45°. It can achieve reliable contact between the electrode and the test sample throughout the test, avoid the influence of small displacement and deformation of the test sample, and has the characteristic of stable current direction.

[0033] In some embodiments, the surface of the punch 1 that contacts the test sample 3 is curved. In some embodiments, the lower part of the die 4 is provided with a threaded interface for connection to a fatigue testing machine, and the side of the punch 1 away from the curved surface is provided with a threaded interface for connection to a fatigue testing machine.

[0034] In some embodiments, the concave mold 4 is further provided with a slot for mounting an optical lens, the slot being perpendicular to and connected to the groove.

[0035] The present invention achieves the placement of the optical lens by opening a slot on the concave mold 4, effectively avoiding the obstruction of the optical observation path during the image acquisition process of the experiment.

[0036] In some embodiments, the clamping component includes a first latch and a second latch, each comprising a plate-shaped member 501 and two engaging members 502 located at both ends of the plate-shaped member 501. Both the first and second latches engage with both sides of the test sample 3 via two corresponding engaging members 502. The plate-shaped member 501 and the two engaging members 502 are integrally formed, and both the plate-shaped member 501 and the engaging members 502 are made of insulating ceramic material; in some specific embodiments, both the plate-shaped member 501 and the engaging members 502 are made of high-strength insulating ceramic, specifically alumina ceramic, with a volume resistivity of 10 Ω·cm. 12 ~10 14 The dielectric strength is 10~15kV / mm, and in some specific embodiments, the electrode is a copper electrode. Both the first and second latches are shaped to match the sample 3 to be tested, and are secured to both sides of the sample 3 via snap-fit ​​components.

[0037] The electrically assisted three-point bending test device with controllable current direction of the present invention, through the cooperation of the first and second clips, enables the electrodes to be quickly installed at both ends of the test sample based on the target current direction before the three-point bending test. Preferably, the first and second clips are made of insulating material, which can ensure that the current only passes through the inside of the test sample, effectively avoiding current leakage from affecting the bending test. It has the characteristics of high test accuracy and high repeatability.

[0038] In some embodiments, the plate-like member 501 has a slot for placing the electrode 6 and a through hole 9 for passing a wire. The wire is connected to the electrode 6.

[0039] In this invention, the wire and the electrode are connected by welding or crimping. Under the dual constraints of the wire's tension and positioning force and the slot's engagement, the electrode is effectively prevented from shaking, ensuring the stability and reliability of the electrode in the plate-shaped component.

[0040] In some embodiments, the snap-fit ​​member 502 has a friction surface 503 on the side near the test sample 3. The friction surface includes a line surface engraved on the side surface or a friction-enhancing film fixed on the side surface; in some specific embodiments, the line surface engraved on the side surface includes a line surface formed by engraving friction-enhancing patterns on the side surface, and the friction-enhancing patterns include parallel lines or intersecting lines; the friction-enhancing film includes an industrial rubber friction-enhancing film or an industrial polyurethane friction-enhancing film.

[0041] The electrically assisted three-point bending test device with controllable current direction of the present invention increases friction by setting a friction surface on the side of the clamping component close to the test sample, thereby preventing the clamp from slipping off during the test and increasing the stability of the clamping.

[0042] In some embodiments, the electrically assisted three-point bending test device with controllable current direction further includes a support rod 2 for supporting the test sample 3, and the concave mold 4 has an opening for the support rod 2 to pass through.

[0043] In some embodiments, the surfaces of the electrically assisted three-point bending test device with controllable current direction that contact the test sample 3 are all covered with an insulating film. By covering all surfaces in contact with the test sample 3 with an insulating film, a stable insulation effect is ensured at the contact interface between the test sample and the test device, effectively avoiding local short circuits. The insulating film is continuous and uniform, and at the same time, it can effectively ensure the uniformity and reliability of force transmission during loading. The surfaces in contact with the test sample 3 include the curved surface of the punch 1 and the support rod 2. In some embodiments, the thickness of the insulating film is 2~10 micrometers, the surface roughness Ra≤0.4μm, and the film thickness error≤±5%. In some embodiments, the material of the insulating film includes alumina and / or silicon nitride, and the volume resistivity of the insulating film is 10. 12~10 14 Ω·cm, dielectric strength > 10 6 V / cm. In some embodiments, the insulating film is prepared by atomic layer deposition, magnetron sputtering, or plasma spraying and thermosetting. In some specific embodiments, the insulating film is an alumina film with a thickness of 5 micrometers and a theoretical breakdown voltage of 500~750 V.

[0044] This invention provides an insulating film with high resistivity and high thermal stability on the surface in contact with the test sample. The theoretical breakdown voltage of this film is set much higher than the loading pulse voltage range (5–20V) under the three-point bending test. Under typical loading conditions with a pulse width not exceeding 10ms and a duty cycle less than 10%, even with a peak current reaching 1000A, breakdown and current leakage do not occur. This electrically assisted three-point bending test device with controllable current direction can effectively achieve precise control of the current path without affecting loading accuracy and sample positioning, and can be used for a long time under high current pulse action.

[0045] On the other hand, a method for preparing the above-mentioned current-direction controllable electrically assisted three-point bending test device is provided, including a method for setting an insulating film on the contact surface with the test sample, comprising using the contact surface with the test sample as a substrate, and setting the insulating film on the contact surface with the test sample by atomic layer deposition, specifically including:

[0046] Step 1: Pretreatment of the substrate surface, specifically including: removing surface organic contaminants and adsorbed moisture by means of plasma cleaning, ultraviolet ozone treatment or chemical solution cleaning, so as to fully expose the active sites on the substrate surface to improve the adhesion and deposition uniformity of the film.

[0047] Step 2, precursor pulse, specifically includes: introducing the metal precursor gas trimethylaluminum (TMA) into the deposition chamber, activating the pulse, causing the metal precursor gas molecules to undergo a saturated adsorption reaction with the active sites on the substrate surface to form a monolayer; the deposition temperature is 150~300℃; the deposition temperature can be 150℃, 200℃ or 300℃.

[0048] Step 3, the purging step, specifically includes: using high-purity nitrogen or argon to purge the deposition chamber to remove unreacted precursor molecules and byproducts, and to avoid gas-phase side reactions;

[0049] Step four, reactive gas pulse, specifically includes: introducing reactive gas into the deposition chamber, activating a pulse to react with the adsorbed precursor molecules, and generating a dense oxide or nitride monolayer film; the reactive gas is an oxidant, including water vapor, ozone, or oxygen plasma; the deposition temperature is 150~300℃; the deposition temperature can be 150℃, 200℃, or 300℃.

[0050] Step 5, Cyclic Deposition, specifically includes: alternating and repeating precursor pulse and reactive gas pulse steps, and obtaining an insulating film with a preset film thickness by controlling the number of cycles.

[0051] By incorporating pretreatment, followed by pulsed precursors and reactive gases, the bonding force between the thin film and the substrate is effectively improved, achieving dense and uniform deposition of insulating thin films. The deposition temperature is 150~300℃. If the temperature is too low, the film is prone to becoming porous, while if the temperature is too high, the film layer will crack or residual stress concentration will occur. Further pulsed precursors or reactive gases also include rotating the substrate, which can effectively ensure the deposition uniformity of complex curved surfaces.

[0052] This invention also provides a method for setting an insulating film on the contact surface with the test sample, wherein the thickness of the resulting insulating film is only 1 / 100 to 1 / 200 of the thickness of a traditional ceramic sleeve, effectively avoiding the loading eccentricity, processing difficulties, and brittleness risk caused by the traditional ceramic sleeve structure. It has higher hardness, wear resistance, and thermal stability than traditional organic insulating films, effectively reducing the occurrence of plastic indentations or peeling. The device of this invention effectively prevents current bypass and local leakage, and features high loading accuracy, long service life, and stable test results.

[0053] The electrically assisted three-point bending test device with controllable current direction of the present invention has a simple structure and is easy to assemble and maintain.

[0054] Furthermore, the present invention provides a method for using the above-mentioned electrically assisted three-point bending test device with controllable current direction, comprising:

[0055] Step 1: Install the two electrodes on the first and second clips respectively, pull out the wires connecting the electrodes from the through hole 9 respectively, and clamp the first and second clips with the electrodes on them onto the test sample 3 respectively, so that the first and second clips are spaced apart and parallel to each other, to obtain the sample assembly.

[0056] Step 2: Place the concave mold 4 on the fatigue machine base, install the support rod 2 on the concave mold 4, and fix it so that it will not rotate or move. Place the sample assembly to be tested in the groove of the concave mold 4 and on the support rod 2. Set an in-situ DIC optical lens in a direction perpendicular to the sample assembly to observe and collect the deformation of the sample 3 to be tested. The method of fixing the support rod 2 can be a conventional method in the art, such as fixing the support rod to the groove with a pin.

[0057] Step 3: Connect the punch 1 thread to the loading end of the fatigue machine, and adjust it so that the curved surface of the punch 1 is aligned with the test sample 3;

[0058] Step 4: Turn on the power supply connected to the electrodes, control the current flow in the electrodes as needed, and start the fatigue test.

[0059] Prior to the application for this invention, a series of experiments were conducted. Some of the experimental results are listed below to provide a more detailed description of the invention. The following is a detailed description in conjunction with the embodiments.

[0060] Example 1

[0061] This embodiment provides an electrically assisted three-point bending test device with controllable current direction, as shown in the schematic diagram below. Figure 1 , Figure 2 and Figure 3 As shown, the device includes a concave mold 4, a convex mold 1, and a clamping component for placing electrodes on the test sample 3, as well as a support rod 2 for supporting the test sample 3. The concave mold 4 has a groove for placing the test sample 3. The convex mold 1 is used to apply a load to the test sample. The surface of the convex mold 1 that contacts the test sample 3 is curved. The concave mold 4 has an opening for the support rod 2 to pass through. The lower part of the concave mold 4 is provided with a threaded interface for connection to a fatigue testing machine.

[0062] In this embodiment, the test sample 3 is a beam-shaped sample with a length of 20 mm, a height of 3 mm, and a width of 6 mm. A notch is pre-made in the center of the bottom surface of the test sample 3 along the width direction. The notch penetrates the sample, with a cut height of about 300 μm and an arc radius of about 100 μm. The notch and the area around it with a width of 500 μm and a height of 1 mm constitute the DIC region of interest for obtaining deformation information.

[0063] In this embodiment, the diameter of the support rod 2 is 3mm, the radius of curvature of the punch 1 is 1.5mm, and the distance between the two support rods 2 installed after the die 4 is 12mm.

[0064] In this embodiment, the clamping component includes a first latch and a second latch. Both the first and second latches include a plate-shaped member 501 and two engaging members 502 located at both ends of the plate-shaped member 501. Both the first and second latches engage with both sides of the test sample 3 via the two corresponding engaging members 502. The plate-shaped member 501 and the two engaging members 502 are integrally formed, and both the plate-shaped member 501 and the engaging members 502 are made of insulating ceramic. Both the plate-shaped member 501 of the first and second latches have slots for placing electrodes and through holes 9 for passing wires.

[0065] In this embodiment, each of the snap-fit ​​members 502 has a friction surface 503 on its side closest to the test sample 3. The friction surface is a line surface formed by friction-enhancing textures engraved on the side, and the friction-enhancing textures are grid-like.

[0066] In this embodiment, the surfaces of the punch 1 and the support rod 2 are both covered with an alumina insulating film.

[0067] This embodiment also provides a method for applying the above-described electric-assisted three-point bending test device with controllable current direction:

[0068] Step 1: Pretreat the above beam-shaped sample to obtain a test specimen 3; the pretreatment includes: spraying a 1-μm diamond aerosol particle polishing solution onto the surface of the beam-shaped sample to cover 50% of the area within the DIC region of interest; that is, half of the area in the DIC region of interest is covered by diamond particles, and the other half remains exposed, so as to form a randomly and uniformly distributed high-contrast speckle pattern on the surface of the specimen, ensuring the tracking accuracy and stability of DIC testing.

[0069] Step 2: With the current direction θ being 30°, determine that the distances between the two electrodes and the center of the test specimen 3 are both 2.57 mm. Use a vernier caliper to measure and determine the accurate snap positions, install the two electrodes on the first snap and the second snap respectively, pull out the wires connected to the electrodes from the through holes 9 respectively, and clamp the first snap and the second snap with the installed electrodes to the upper surface and the lower surface of the test specimen 3 according to the preset snap positions respectively to obtain a specimen assembly. Set the current loading scheme in the electrodes as follows: peak current 300 A, pulse width 5 ms, duty cycle 5%, and pulse current frequency 1 Hz.

[0070] Step 3: Place the female die 4 on the base of the Instron 8801 electro-hydraulic servo fatigue testing machine through the threaded interface at its lower part, install the support rod 2 on the female die 4, and use a pin to fix it so that it will not rotate or move. Place the specimen assembly in the groove of the female die 4 and make it located on the support rod 2. Set an in-situ DIC optical lens in the direction perpendicular to the specimen assembly, and there is no obstruction between the in-situ DIC optical lens and the test specimen 3; the in-situ DIC optical lens includes a Questar QM-100 long-focus microscope and a QIClick 8-megapixel, 12-bit digital camera, and the spatial resolution is about 3 μm.

[0071] Step 4: Threadedly connect the punch 1 to the loading end of the Instron 8801 electro-hydraulic servo fatigue testing machine, and adjust to make the surface of the punch 1 centered on the test specimen 3.

[0072] Step 5: Run the WaveMatrix software supporting the fatigue testing machine, and set the loading scheme as follows: First, make the load linearly rise from the valley value of 100 N to the peak value of 1000 N within 2 seconds and maintain it for 5 seconds to achieve peak load holding; then, make the load linearly drop back from 1000 N to 100 N within 2 seconds and maintain it for 1 second; repeat 1000 times to achieve typical load-holding fatigue including peak and valley load-holding segments, and the load frequency is 0.1 Hz.

[0073] Step 6: Set the in-situ DIC optical lens image acquisition frequency to 1Hz;

[0074] Step 7: Activate the pulse current control switch to energize the two electrodes according to the current loading scheme described above. Use a thermal imager to test the surface temperature of the test sample. After the surface temperature stabilizes, start the in-situ DIC optical lens image acquisition. Start the fatigue testing machine to apply a load vertically to the test sample 3 according to the loading scheme described above. During the loading process, the in-situ DIC optical lens records the micro-deformation behavior of the test sample 3 under mechanical loading in situ throughout the entire process, capturing the peak and trough data in each fatigue cycle.

[0075] Step 8: After reaching the required number of cycles, turn off the pulse current control switch, remove the test sample 3, save the data, and complete the three-point bending test. An optical photograph of the test setup is shown below. Figure 4 As shown.

Claims

1. A current-direction controllable electrically assisted three-point bending test device, characterized in that, It includes a concave mold (4), a convex mold (1), and a clamping component for placing an electrode (6) on a test sample (3). The concave mold (4) has a groove for placing the test sample (3).

2. The electrically assisted three-point bending test device with controllable current direction according to claim 1, characterized in that, The clamping component includes a first buckle and a second buckle, each of which includes a plate-shaped member (501) and two snap-fit ​​members (502) located at both ends of the plate-shaped member (501).

3. The electrically assisted three-point bending test device with controllable current direction according to claim 1, characterized in that, Both the first and second buckles are made of insulating ceramic.

4. The electrically assisted three-point bending test device with controllable current direction according to claim 2, characterized in that, Each plate (501) has a slot for placing an electrode (6) and a through hole (9) for passing a wire.

5. The electrically assisted three-point bending test device with controllable current direction according to claim 2, characterized in that, The snap-fit ​​component (502) has a friction surface (503) on the side near the test sample (3).

6. The electrically assisted three-point bending test device with controllable current direction according to claim 1, characterized in that, The electrically assisted three-point bending test device with controllable current direction also includes a support rod (2) for supporting the test sample (3), and the die (4) has an opening for the support rod (2) to be inserted.

7. The electrically assisted three-point bending test device with controllable current direction according to claim 1, characterized in that, The surfaces of the electrically assisted three-point bending test device with controllable current direction that come into contact with the test sample (3) are all covered with an insulating film.

8. A method for preparing an electrically assisted three-point bending test device with controllable current direction as described in claim 7, characterized in that, This includes a method of covering an insulating film with the surface in contact with the test sample (3) as a substrate, specifically including: Step 1: Clean the surface of the substrate; Step 2: Deposit the metal precursor onto the cleaned substrate surface using pulse deposition; Step 3: Purge; Step 4: Deposit the reactive gas onto the purged surface using pulse deposition.

9. The method according to claim 8, characterized in that, In step two, the metal precursor is gaseous trimethylaluminum, and the deposition temperature in step two is 150℃~300℃; in step four, the reaction gas is water vapor, ozone or oxygen, and the deposition temperature in step four is 150~300℃.

10. A method for using the electrically assisted three-point bending test device with controllable current direction as described in claim 1, characterized in that, include: Insert the electrode (6) into the clamping component; The clamping component with the electrode (6) is clamped onto the test sample (3) and placed in the groove of the die (4). The punch (1) is adjusted so that it faces the test sample (3).

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