Electroplastic in-situ testing method and electroplastic in-situ testing device

Abstract

The invention provides an electroplastic in-situ testing method and an electroplastic in-situ testing device, and relates to the technical field of in-situ tests.The method comprises the steps that a metal sample is prepared, and the metal sample comprises a micro-column structure; electrically connecting one pole of a pulse power supply with the metal sample, and electrically connecting the other pole with the pressure head; pressing a pressure head on the micro-column structure, regulating and controlling the output current of the pulse power supply, and regulating and controlling the stress of the pressure head on the micro-column structure, so that the micro-column structure generates plastic deformation; and recording the plastic deformation process of the micro-column structure by using a scanning electron microscope to obtain a corresponding relation among output current, stress and deformation. According to the device and the method, metal electroplasticity in-situ testing can be realized, and the dynamic deformation process and structural evolution of a micro-nano-scale micro-column structure can be clearly and continuously captured and recorded.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of in-situ testing, in particular to an electroplastic in-situ testing method and an electroplastic in-situ testing device. BACKGROUND

[0002] In the traditional experimental method, the metal electroplastic effect research can only compare the macroscopic performance data before and after electroplastic processing, such as rheological stress reduction or plasticity improvement. And the microstructure is analyzed destructively after the event, which cannot obtain the microstructure evolution data in the process of pulse current treatment, such as grain morphology change, dislocation slip and twin activation and other defects. These microstructure evolution data are the cause, and the macroscopic change is the result. At the same time, the mechanism of the interaction between the joule heat effect and the non-thermal effect of the pulse current is complex, and it has been difficult to distinguish for a long time. Although some researchers have suppressed the thermal effect by air convection or liquid nitrogen cooling to study the non-thermal effect alone, the experimental operation is complicated and still limited to macroscopic research. At present, there is no method to obtain the microstructure evolution data of the metal electroplasticity. SUMMARY

[0003] The present application proposes an electroplastic in-situ testing method and an electroplastic in-situ testing device, which aims to obtain a method for obtaining microstructure evolution data of metal electroplasticity.

[0004] To achieve the above purpose, the embodiment of the present application provides an electroplastic in-situ testing method, which comprises: preparing a metal sample, the metal sample comprising a micro-column structure; electrically connecting one pole of a pulse power supply to the metal sample and electrically connecting the other pole to a pressure head; pressing the pressure head on the micro-column structure, adjusting the output current of the pulse power supply, and adjusting the stress of the pressure head on the micro-column structure, so that the micro-column structure produces plastic deformation; recording the plastic deformation process of the micro-column structure by using a scanning electron microscope, and obtaining the corresponding relationship between the output current, the stress and the deformation.

[0005] The above in-situ test method of electroplasticity is realized by electrically connecting one pole of the pulse power supply to the metal sample and electrically connecting the other pole to the indenter to form an electric circuit among the indenter, the metal sample and the pulse power supply. The stress of the micro-column structure on the indenter can be adjusted by adjusting the indenter. Thus, the in-situ test of the micro-column structure is realized under the adjustment of the current and the pressure. The dynamic deformation process and the structural evolution of the micro-column structure can be clearly and continuously captured and recorded by the high spatial resolution and real-time imaging function of the scanning. Based on the above example, the influence of the Joule heating effect and the non-thermal effect on the micro-column structure can be further understood based on the control of the current and the stress. The above in-situ compression test of the micro-column structure by force-electricity coupling can establish the relationship between the pulse current and the microstructure evolution, and can directly construct and reveal the internal correlation among the current parameters, the microstructure evolution and the mechanical properties, which can provide a key platform support for in-depth exploration of the electroplasticity effect mechanism at the nanoscale, and can promote the development of high-performance metal materials. In some embodiments, the method of regulating the output current of the pulse power supply comprises: regulating the frequency, duty cycle or current density of the pulse power supply to regulate the proportion of the Joule heating effect and the non-thermal effect of the output current.

[0006] In some embodiments, the metal sample is prepared by: laser marking a first metal substrate to assist in positioning the grains; laser marking a first surface of the first metal substrate to assist in positioning the grains, and pasting a wire on a second surface of the first metal substrate after the laser marking to obtain a second metal substrate; the first surface and the second surface are opposite; and cold mounting the second metal substrate by using a resin and a curing agent. The second metal substrate after the cold mounting is polished to remove the oxide layer and the deformation layer on the surface of the metal substrate. The second metal substrate after the polishing is surface gold-plated to obtain the metal sample.

[0007] In some embodiments, the pressing of the indenter on the micro-column structure comprises: installing the indenter on a fine adjustment table of an in-situ test device, and fixing the metal sample on a displacement table of the in-situ test device; installing the in-situ test device in a scanning electron microscope, electrically connecting one pole of the pulse power supply to the wire pasted on the metal sample, and electrically connecting the other pole to the indenter; controlling the displacement table to move, and moving the micro-column structure of the metal sample to below the indenter; and controlling the fine adjustment table to move, and pressing the indenter on the micro-column structure to generate a pre-stress.

[0008] In some embodiments, the range of the pre-stress is 0.3 mN-0.5 mN. In some embodiments, the in-situ test device and the scanning electron microscope are electrically connected, and the reference potential of the in-situ test device is consistent with that of the scanning electron microscope.

[0009] In some embodiments, the metal sample is prepared, comprising: laser marking a first surface of a first metal substrate to assist in positioning a grain; pasting a lead wire on a second surface of the first metal substrate after marking to obtain a second metal substrate; the first surface and the second surface being opposite; cold mounting the second metal substrate with a resin and a curing agent; polishing the second metal substrate after mounting to remove an oxidation layer and a deformation layer on a surface of the metal substrate; surface gold spraying the second metal substrate after polishing to obtain the metal sample; and obtaining grain orientation and morphology information of the metal sample based on electron backscatter diffraction. In some embodiments, the metal sample is prepared, further comprising: obtaining grain orientation and morphology information of the metal sample based on electron backscatter diffraction; and placing the metal sample into a scanning electron microscope, and cutting the metal sample to obtain the micro-column structure using a poly-ion beam based on the grain orientation and the morphology information.

[0010] In some embodiments, a center position is selected, and a ring pattern with an inner diameter of 12 μm and an outer diameter of 35 μm is cut based on the center position, and material around the outer diameter is removed; at the center position, a micro-column roughcast with a diameter of 6.5 μm and a height of 5 μm is obtained by further cutting; and a ring pattern with an inner diameter of 6 μm and an outer diameter of 20 μm is cut based on the center position to obtain a metal structure with a diameter of 5 μm and a height of 10 μm.

[0011] In some embodiments, the metal structure with a diameter of 5 μm and a height of 10 μm is refined.

[0012] In another aspect, the application provides an in-situ test device for electroplasticity, which comprises a scanning electron microscope, an in-situ test device, a pulse power supply and a controller. The scanning electron microscope; the in-situ test device is installed in the scanning electron microscope, and comprises a fine adjustment stage, a pressure head installed on the fine adjustment stage and a displacement stage; the metal sample comprises a micro-column structure, and the displacement stage is used to move the metal sample so that the micro-column structure is moved to below the pressure head; the pulse power supply has one pole electrically connected to the metal sample and the other pole electrically connected to the pressure head; the fine adjustment stage is used to move the pressure head so that the pressure head is pressed on the micro-column structure; the first controller is electrically connected to the scanning electron microscope; the second controller is electrically connected to the in-situ test device; the third controller is electrically connected to the pulse power supply; the third controller is used to regulate the output current of the pulse power supply; the second controller is used to control the displacement stage to move the metal sample and control the fine adjustment stage to move the pressure head, so as to regulate the stress of the pressure head on the micro-column structure and make the micro-column structure produce plastic deformation; and the first controller is used to control the scanning electron microscope to record the plastic deformation process of the micro-column structure, so as to obtain the corresponding relationship among the output current, the stress and the deformation. The in-situ test device for electroplasticity in the above embodiment can realize the electrical connection loop among the pressure head, the metal sample and the pulse power supply, and realize the in-situ test of electroplasticity. Moreover, the high spatial resolution and real-time imaging function of the scanning electron microscope can clearly and continuously capture and record the dynamic deformation process and structure evolution of the micro-column structure in micro-nano scale. Moreover, the stress of the pressure head on the micro-column structure can be adjusted through the setting of the pressure head. In this way, the in-situ test of electroplasticity of the micro-column structure is realized under the regulation of the current and the pressure. Moreover, the parameters such as the size, frequency and duty cycle of the pulse current are continuously adjustable within a certain range, so as to regulate the average current density and the peak current density, and further understand the influence of the Joule heating effect and the non-thermal effect on the micro-column structure. The in-situ test device for electroplasticity in the above embodiment can establish the relationship between the pulse current and the microstructure evolution through the force-electricity coupling in-situ compression test of the micro-column structure, and can directly construct and reveal the internal correlation law among the current parameters, the microstructure evolution and the mechanical properties. Finally, the above embodiment can provide a key platform support for in-depth exploration of the electroplasticity effect mechanism in nano scale, and promote the development of high-performance metal materials. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the application, the following will briefly introduce the drawings needed to be used in some embodiments of the application. Obviously, the drawings in the following description are only some drawings of the embodiments of the application, and other drawings can also be obtained by those skilled in the art according to these drawings. In addition, the drawings in the following description can be regarded as schematic diagrams, and are not the actual size of the product involved in the embodiments of the application or the actual process of the method.

[0014] Figure 1 A flow chart of an electroplasticity in-situ test method provided by the embodiments of the application; Figure 2 A comparison chart before and after the pressure head exerts stress on the micro column structure provided for an embodiment of the present application; Figure 3 A schematic diagram of the corresponding relationship of output current, stress and displacement of the micro column structure provided for an embodiment of the present application. DETAILED DESCRIPTION

[0015] The technical solutions in some embodiments of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all. Based on the embodiments provided by the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present application.

[0016] Unless otherwise required by the context, throughout the specification and claims, the term "comprising" is to be interpreted as open, inclusive, meaning "including, but not limited to".

[0017] Hereinafter, the terms "first" and "second" are used only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first" and "second" can explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0018] In describing some embodiments, the term "connected" and its derivatives can be used. The term "connected" should be interpreted broadly, for example, "connected" can be fixedly connected, or detachably connected, or integrated. It can be directly connected, or indirectly connected through an intermediate medium. For example, in describing some embodiments, the term "connected" can be used to indicate that two or more components have direct physical or electrical contact with each other.

[0019] In addition, the use of "based on" means open and inclusive, because the process, step, calculation or other action "based on" one or more conditions or values can be based on additional conditions or values in practice.

[0020] Electroplastic processing is an advanced manufacturing technology that uses pulse current to assist metal plastic deformation. By applying high-density current, the deformation resistance can be greatly reduced, and the material has good plastic deformation ability at a lower temperature. This technology has important significance for the processing and forming of easily oxidized and difficultly deformed metals. The electroplastic effect caused by the interaction between pulse current and the processed material is a composite effect, mainly embodied in joule heat effect and non-thermal effect. The two effects work together to enhance dislocation movement, improve processing capacity, inhibit defect generation, and ultimately improve the mechanical properties and surface quality of the workpiece. In the process of electroplastic processing, thermal effect and non-thermal effect are both competitive and dependent, and the mechanism of action with the internal structure of the material is complex. Due to the lack of direct research means, the further development of electroplastic processing technology is limited. Micro-column structure in-situ compression test, by compressing micron / nanometer-sized columns (usually 0.1-10 μm in diameter), combined with scanning electron microscopy for real-time observation, can directly reveal the plastic deformation, dislocation movement, size effect and defect evolution of metal materials. However, the current in-situ mechanical testing technology is relatively mature, which is only mechanical testing or force-thermal coupling testing. Force-electricity coupling, especially with pulse current, is still difficult to achieve.

[0021] Currently, the technical problems of force-electricity coupling test mainly revolve around two aspects: one is the micro-column structure sample preparation technology, and the other is the stability and characterization of force-electricity coupling in-situ compression test under electron microscope. First, the contact area of micro / nano-scale micro-column structure with the indenter is too small, and some metals are easily oxidized to form an insulating layer on the surface, resulting in too large contact resistance and making it difficult to apply pulse current for electroplastic research. At the same time, for the preparation of single crystal micro-column with specific orientation, there is a lack of method for positioning the single crystal with specific orientation between different electron microscope devices. Second, in the aspect of electroplastic characterization, the periodic discharge of pulse power causes temperature change of metal due to joule heat effect, and the micro-column structure expands and contracts. When the current density exceeds a certain critical value, the micro-column contraction causes the circuit to be disconnected (disconnected from the contact point) and the current cannot be turned on again. Moreover, the application of pulse current and the connection of external equipment will interfere with the electron microscope imaging, which is not conducive to real-time observation.

[0022] As shown in Figure 1 , the embodiment of the present application provides an electroplastic in-situ test method, which specifically comprises: preparing a metal sample, the metal sample comprising a micro-column structure. One pole of a pulse power supply is electrically connected to the metal sample, and the other pole is electrically connected to the indenter. The indenter is pressed against the micro-column structure, the output current of the pulse power supply is regulated, and the stress of the indenter on the micro-column structure is regulated, so that the micro-column structure produces plastic deformation. The plastic deformation process of the micro-column structure is recorded by a scanning electron microscope, and the corresponding relationship between the output current, stress and deformation is obtained.

[0023] For example, the indenter can be a tungsten indenter. A 10 μm diameter tungsten indenter is mounted on the sensor of the in-situ testing system. The metal sample with micro-pillar structure is fixed on the sample stage by conductive glue. The whole testing device is installed in the scanning electron microscope and connected to the controller and pulse power supply by wires. The electron microscope is closed and vacuum is extracted. In the scanning electron microscope, the nano-force stage is tilted at 30°~45°. The micro-pillar structure and the tungsten indenter are observed in the field of view. The three-dimensional displacement stage is controlled by the system controller to move the sample, and the micro-pillar structure in the metal sample is moved to below the tungsten indenter. The tungsten indenter is slowly moved to contact the micro-pillar by the one-dimensional fine adjustment stage, and at this time, a loop is formed between the tungsten indenter, the metal sample and the pulse power supply. After the loop is formed, the current parameters are edited, for example, a direct current or pulse current (frequency <350KHz, duty cycle <95%) output of 0-0.3A can be achieved. Then the pulse current driving module is started, and the current passes through the micro-pillar structure. The force-displacement curve displayed in the computer is controlled to fluctuate under the influence of the pulse current, and 40~60s is waited for stable test data. The current is kept on, the compression parameters are edited on the software in the control computer, and the tungsten indenter is compressed at a certain rate. The force-displacement data is collected, the electroplastic phenomenon is observed in real time, the pulse current parameters or compression conditions are adjusted, and the corresponding relationship between the mechanical behavior and the deformation mode evolution is established.

[0024] As shown in Figure 2 , the details of the micro-pillar structure before and after the force-electricity coupling compression test are shown, wherein, Figure 2 (a) is a detail view of the micro-pillar structure before the test, Figure 2 (b) is a detail view of the micro-pillar structure after 50% strain is applied. As can be clearly seen from the figure, the micro-pillar structure has changed obviously, and the slip traces can be clearly observed.

[0025] As shown in Figure 3 , a schematic diagram of the corresponding relationship of current, stress and displacement is shown. As can be seen from Figure 3 , as the force applied by the indenter increases, the deformation of the metal sample increases. Under the same force, the greater the current, the more obvious the metal softening displacement.

[0026] The in-situ test method for electroplasticity provided by the above embodiment realizes in-situ test of electroplasticity by electrically connecting one pole of the pulse power supply to the metal sample and electrically connecting the other pole to the indenter, forming an electric circuit among the indenter, the metal sample and the pulse power supply, and adjusting the stress of the micro-column structure by adjusting the indenter. In this way, under the adjustment of the current and the pressure, the in-situ test of the micro-column structure is realized. The high spatial resolution and real-time imaging function of scanning are also used to clearly and continuously capture and record the dynamic deformation process and structural evolution of the micro-column structure in micro-nano scale. Based on the above embodiment, the influence of the Joule heating effect and the non-thermal effect on the micro-column structure can be further understood based on the control of the current and the stress. The above in-situ compression test of the force-electric coupling of the micro-column structure establishes the relationship between the pulse current and the microstructure evolution, which can directly construct and reveal the internal correlation between the current parameters, the microstructure evolution and the mechanical properties, and can provide key platform support for in-depth exploration of the mechanism of the electroplasticity effect in nanoscale, and promote the development of high-performance metal materials.

[0027] In some embodiments, the output current of the pulse power supply is adjusted, including adjusting the frequency, duty cycle or current density of the pulse power supply, to adjust the proportion of the Joule heating effect and the non-thermal effect of the output current.

[0028] In the above embodiment, the Joule heating effect is the phenomenon that the micro-column structure changes in microstructure due to heat generated when the current passes through the micro-column structure. The non-thermal effect is the phenomenon that the micro-column structure changes in microstructure due to the action of the current. By controlling the frequency, duty cycle and current density of the pulse power supply, the number of pulse repetitions per unit time, the proportion of current conduction time in a single pulse cycle, the peak current per unit area, and the non-thermal effect can be controlled, and the proportion of the non-thermal effect and the Joule heating effect can be further controlled. Based on the control of the proportion of the non-thermal effect and the Joule heating effect, the exact role of the Joule heating effect and the non-thermal effect in the activation, movement and transformation of the deformation mode can be directly verified. The continuous and accurate adjustment of the pulse current establishes the internal relationship among the current parameters, the microstructure evolution and the mechanical properties.

[0029] The above-mentioned in-situ test method of electroplasticity can only indirectly analyze the structural and performance changes of the material before and after power on in a macroscopic manner compared to the traditional experimental method, and it is difficult to distinguish the limitations of the thermal effect and the non-thermal effect of the pulse current. The present application effectively solves the core problem that the relationship between the electroplasticity effect and the microstructure evolution cannot be established, and it is difficult to quantitatively analyze the strengthening and toughening mechanism. Specifically, the present application realizes: real-time dynamic observation, which can observe the instantaneous initiation, slip, growth, proliferation and annihilation of crystal defects such as dislocations and twins in the process of applying pulse or continuous current in-situ and in real time. Moreover, it can directly prove the exact role of the Joule heat effect and the non-thermal effect in the activation, movement and transformation of the deformation mode, and effectively distinguish between the two. It can also accurately control the current parameters (such as pulse width, frequency, current density), and can synchronously observe the immediate response of the microstructure, collect stress-displacement data, and thus establish an accurate quantitative relationship between the current process parameters, micro-evolution and mechanical behavior.

[0030] In some embodiments, the preparation of the metal sample comprises the following steps: laser marking the first surface of the first metal substrate to assist in positioning the grains; pasting a lead wire on the second surface of the first metal substrate after marking to obtain a second metal substrate; the first surface and the second surface are opposite; cold mounting and embedding the second metal substrate with resin and curing agent. Polishing the embedded second metal substrate to remove the oxide layer and deformation layer on the surface of the metal substrate. Surface gold spraying treatment is performed on the second metal substrate after polishing to obtain a metal sample.

[0031] Taking the preparation of magnesium alloy metal samples as an example, magnesium alloy blocks with sides of 10 mm and a thickness of 1 mm were cut and placed in a ceramic boat. A tube furnace (BF-1200) was used for high-temperature homogenization at 450 degrees Celsius for 5 days under an argon protective atmosphere (95% argon + 5% hydrogen) to obtain single-crystal particles with a diameter of approximately 100-200 μm. Then, laser marking was used for positioning. In the laser marking machine software, 40% power, 2 kHz frequency, and 5 ns pulse width were selected for printing for 40 seconds, forming rectangular patterns with sides of 1 mm on the magnesium alloy surface to assist in positioning the grains. Copper wires were then attached to the back of the magnesium alloy using conductive silver paste. The magnesium alloy blocks were then cold-embedded with resin and a curing agent (with the copper wires exposed), and allowed to stand for two hours to cure. Polishing was then performed, specifically: first, polishing with 400-grit SiC sandpaper for 4 minutes, then with 800-grit SiC sandpaper for 2 minutes, then with 1200-grit sandpaper for 2 minutes, and finally with 2500-grit sandpaper for 4 minutes. After grinding, polishing is performed. The specific polishing process is as follows: first, polishing with 3µm diamond polishing slurry for 6 minutes, then with 1µm diamond polishing slurry for 6 minutes, then with 0.05µm SiO2 polishing slurry for 20 minutes, and finally with 6kV argon particles for 20 minutes. This removes the oxide and deformation layers on the magnesium alloy surface, reducing contact resistance while ensuring the accuracy of test data. Alternatively, the magnesium alloy surface can be sputter-coated with gold. The magnesium alloy sample is placed in a gold sputtering instrument and sputtered with gold at 30mA for 100 seconds, forming a nanoscale gold layer on the magnesium alloy sample surface, delaying oxidation and improving conductivity.

[0032] In the above embodiments, laser marking machines are used to mark and scribble on the surface of the metal sample to assist in the positioning of single or polycrystalline materials. The laser marking machine is a device that uses a high-energy laser beam to create marks on the material surface. Attaching wires to the first metal substrate is to reduce resistance during subsequent electrical connections. A second metal substrate is cold-mounted using resin and a curing agent. Polishing the embedded second metal substrate removes the oxide and deformation layers from its surface. Similarly, surface gold spraying on the polished second metal substrate to obtain the metal sample prevents subsequent oxidation, which could affect the subsequent electrical connections. In summary, to address the problem of excessive contact resistance in micropillar structures due to easy oxidation of metals, making it difficult to apply pulsed current, wires are attached to the metal sample to assist current conduction. Resin and a curing agent are used for embedding, followed by polishing and gold spraying on the front side of the sample. This isolates water molecules and oxygen from the air, delays metal oxidation, improves contact resistance, and enhances conductivity. This processing method greatly expands the testing scope of the above-mentioned technologies, enabling in-situ electroplasticity testing of gold, silver, iron, and easily oxidized metals or alloys such as magnesium, copper, and titanium, and studying the influence of alloying elements on the electroplasticity effect for micropillars with different compositions.

[0033] In some embodiments, the pressing head is pressed against the micro-column structure, comprising: in some embodiments, the pressing head is pressed against the micro-column structure, comprising: mounting the pressing head on a fine adjustment stage of an in-situ testing device, and fixing the metal sample on a displacement stage of the in-situ testing device; mounting the in-situ testing device in a scanning electron microscope, one pole of a pulse power source is electrically connected to the lead wire pasted on the metal sample, and the other pole is electrically connected to the pressing head; controlling the displacement stage to move, and moving the micro-column structure of the metal sample to below the pressing head; controlling the fine adjustment stage to move, and pressing the pressing head against the micro-column structure to generate a pre-stress. In the above-mentioned embodiments, the pressing head is a conductive pressing head, which can be selected as a tungsten steel pressing head. By mounting the pressing head on the fine adjustment stage of the in-situ testing system, and fixing the metal sample on the displacement stage of the in-situ device, and controlling the displacement stage to move the micro-column structure to below the pressing head, the in-situ testing system can be controlled to control the stress applied to the micro-column structure by the pressing head. By connecting the two poles of the pulse power source to the pressing head and the lead wire pasted on the metal sample respectively, a closed loop between the pulse power source, the pressing head and the metal sample can be formed after the pressing head and the micro-column structure are in contact, and the current passing through the micro-column structure can be controlled by controlling the pulse power source.

[0034] Further, controlling the fine adjustment stage to move, and pressing the pressing head against the micro-column structure to generate a pre-stress, can make the pressing head and the micro-column structure contact more closely to establish a stable connection, and reduce the possibility of open circuit caused by metal contraction during power-on.

[0035] In some embodiments, the pre-stress is in the range of 0.3mN-0.5mN.

[0036] In the above-mentioned embodiments, if the pre-stress is too small, the micro-column structure may be contracted due to thermal effects or other effects, and open circuit may occur. If the pre-stress is too large, the micro-column structure may be changed by the pressing head. Therefore, the range of the pre-stress is crucial to the entire test.

[0037] In some embodiments, the in-situ testing device is electrically connected to the scanning electron microscope, and the reference potential of the in-situ testing device is consistent with that of the scanning electron microscope.

[0038] In the above-mentioned embodiments, by making the reference potential of the in-situ testing device consistent with that of the scanning electron microscope, signal interference can be reduced, and the imaging quality of the scanning electron microscope can be ensured.

[0039] In some embodiments, the metal sample is prepared, further comprising: obtaining the grain orientation and topography information of the metal sample based on electron backscatter diffraction; based on the grain orientation and topography information, and in combination with the positioning line of the laser marking, the metal sample is placed into the scanning electron microscope, and a poly-ionic beam is used to cut the metal sample to obtain the micro-column structure.

[0040] In the above embodiments, the electron backscattering diffraction core is based on the diffraction signal generated by the interaction of the electron beam with the sample to further deduce the crystal structure information and topography information. Based on electron backscattering diffraction, the grain morphology and orientation information of the metal sample can be accurately obtained. Then the positioning line based on laser marking is used to determine the position of the measured grain. Then the metal sample is placed in the electron microscope, and based on the positioning line, a single crystal microcolumn structure with the same orientation is cut inside the measured grain. Based on laser marking positioning, the same area of the sample can be measured and processed between different electron microscopes.

[0041] Further, the poly-ion beam technology can cut and process polycrystalline and single crystal microcolumns (the microcolumns can be cylindrical or polygonal, and the typical diameter / edge length is 100 nm-10 μm, and the height is about 2-3 times the diameter / edge length), and separate and study the influence of single microscopic elements (such as single crystal orientation, grain boundary, and phase boundary).

[0042] It can be understood that the grain size significantly affects the deformation mechanism and mechanical behavior of the metal material. Within a certain range, the grain size decreases, the grain boundary strengthening effect is enhanced, and the material strength is improved. At the same time, small grains can better coordinate deformation and inhibit crack propagation, thereby improving the plasticity of the material. When the grain size is refined to the sub-micron / nanometer level, the grain boundary mobility is enhanced and loses the strengthening property, but can adapt to plastic deformation through grain boundary sliding or grain rotation. At this time, the strength of the material is reduced and the plasticity is significantly improved, and even exhibits superplasticity. Finite element simulation and macroscopic test results show that due to the existence of orientation difference between adjacent grains, a potential difference is generated on both sides of the grain boundary after the pulse current is passed, providing additional power to promote grain boundary sliding or grain rotation. By performing force-electricity coupling in-situ compression on polycrystalline microcolumns with different grain sizes, the mechanical behavior of the grains and grain boundaries under the influence of the pulse current can be directly displayed, the correlation between the grain size, the pulse current, and the grain boundary deformation behavior is established, and the strength and plasticity of the material are helped to be regulated.

[0043] Based on the above polycrystal, further say single crystal, grain interior can produce slip and twinning accommodation deformation along a certain crystal face and a certain crystal direction, the difficulty of activation of different deformation modes is different, such as magnesium and most magnesium alloys have close-packed hexagonal structure, the lattice symmetry is poor, the critical shear stress required for the activation between the most difficult to activate pyramidal slip and the most easy to activate basal slip is different by dozens of times, resulting in less available deformation mode of magnesium alloy and poor plastic processing capacity. Grain orientation will significantly affect the activation of deformation mode, therefore, in-situ compression of single crystal microcolumn with different orientation can systematically study the effect of pulse current on the initiation, slip, growth and transformation of different deformation modes, and establish the relationship between grain orientation, pulse current and deformation mode transformation, providing a theoretical basis for the electroplastic processing of metal materials, especially the forming of difficult-to-process metals. Single crystal microcolumn preparation requires long time high temperature heat treatment of metal materials to generate coarse grains, and the grain orientation and morphology information is obtained by electron backscatter diffraction technology, combined with polyion beam technology to cut and prepare single crystal microcolumn with specified orientation. Among them, different scanning electron microscopes are used for grain structure information acquisition and single crystal microcolumn processing, and laser marking machine is used to print marks on the surface of metal sample to assist positioning single crystal, so as to cut microcolumn in the grain with specific orientation.

[0044] In summary, the microcolumn structure can realize composition and structure customization. The electroplasticity test of polycrystal or single crystal microcolumn with specific orientation of different compositions can help understand the effect of pulse current on grain boundary and intracrystalline deformation mode from different angles, which is of great significance to the development of electroplastic processing technology of metal materials and the preparation of high-performance metals.

[0045] Another aspect of the present application provides an electroplasticity in-situ testing device, a scanning electron microscope; an in-situ testing device installed in the scanning electron microscope, the in-situ testing device comprising a fine adjustment stage, a pressure head installed on the fine adjustment stage and a displacement stage; a metal sample comprising a microcolumn structure, the displacement stage being used to move the metal sample so that the microcolumn structure moves to the lower side of the pressure head; a pulse power supply, one pole being electrically connected with the metal sample, and the other pole being electrically connected with the pressure head; the fine adjustment stage being used to move the pressure head so that the pressure head is pressed on the microcolumn structure; a first controller being electrically connected with the scanning electron microscope; a second controller being electrically connected with the in-situ testing device; a third controller being electrically connected with the pulse power supply; the third controller being used to regulate the output current of the pulse power supply; the second controller being used to control the displacement stage to move the metal sample, and control the fine adjustment stage to move the pressure head, so as to regulate the stress of the pressure head on the microcolumn structure, and make the microcolumn structure produce plastic deformation; the first controller being used to control the scanning electron microscope to collect the displacement of the plastic deformation of the microcolumn structure, and obtain the corresponding relationship among the output current, the stress and the displacement.

[0046] In some embodiments, the cutting of the metal sample to obtain the micro-pillar structure comprises: tilting the sample stage by 52°, at which time the ion gun is perpendicular to the sample surface, selecting a position center, and cutting a ring pattern with an inner diameter of 12 μm and an outer diameter of 35 μm using a very high ion beam current (0.1 μA) to quickly remove the surrounding material and obtain a micro-pillar roughcast with a diameter of 6.5 μm and a height of 5 μm at the center. Based on the position center, a ring pattern with an inner diameter of 6 μm and an outer diameter of 20 μm is cut using a smaller ion beam current (9.3 na) to obtain a metal structure with a diameter of 5 μm and a height of 10 μm.

[0047] In some embodiments, the cutting of the metal sample to obtain the micro-pillar structure further comprises: finishing the metal structure with a diameter of 5 μm and a height of 10 μm, specifically: polishing the micro-pillar using an ion beam current of 80 pa to reduce the taper and polish the surface.

[0048] In the above embodiments, the cutting of the micro-pillar structure not only eliminates the non-uniformity of the microstructure, but also separates and studies a single microelement. In-situ compression of the micro-pillar structure based on force-electricity coupling can directly establish a quantitative relationship between the pulsed current, the microstructure evolution (such as an increase in dislocation density, a deformation mode transition, etc.) and the mechanical properties, and can observe the deformation mechanism in real time.

[0049] The in-situ testing device for electroplasticity in the above embodiments can realize an electrical connection loop among the indenter, the metal sample and the pulsed power supply, and realize in-situ testing of electroplasticity. Moreover, by using the high spatial resolution and real-time imaging function of the scanning electron microscope, the dynamic deformation process and structure evolution of the micro-pillar structure at the micro / nano scale can be clearly and continuously captured and recorded. Moreover, by setting the indenter, the stress of the indenter on the micro-pillar structure can be adjusted. In this way, under the regulation of the current and the pressure, in-situ testing of the micro-pillar structure based on electroplasticity is realized. Moreover, based on the controller, the current and the stress can be controlled, and the influence of the Joule heating effect and the non-thermal effect on the micro-pillar structure can be further understood. The in-situ testing device for electroplasticity in the above embodiments establishes the relationship between the pulsed current and the microstructure evolution by in-situ compression testing of the micro-pillar structure based on force-electricity coupling, and can directly construct and reveal the internal correlation law among the current parameters, the microstructure evolution and the mechanical properties. Finally, the above embodiments can provide a key platform support for in-depth exploration of the electroplasticity effect mechanism at the nano scale, and promote the development of high-performance metal materials.

[0050] The above merely describes specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art who conceives changes or substitutions within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for in-situ testing of electroplasticity, characterized in that, include: Prepare a metal sample, wherein the metal sample comprises a micropillar structure; One pole of the pulse power supply is electrically connected to the metal sample, and the other pole is electrically connected to the pressure head; The pressure head is pressed against the micro-pillar structure, the output current of the pulse power supply is adjusted, and the stress of the pressure head on the micro-pillar structure is adjusted, so that the micro-pillar structure undergoes plastic deformation. The plastic deformation process of the micropillar structure was recorded using a scanning electron microscope to obtain the corresponding relationship between output current, stress, and deformation.

2. The in-situ electroplasticity testing method according to claim 1, characterized in that, Regulating the output current of the pulse power supply includes: The frequency, duty cycle, or current density of the pulse power supply are adjusted to regulate the ratio of Joule thermal effect to non-thermal effect in the output current.

3. The in-situ electroplasticity testing method according to claim 1, characterized in that, Preparation of metal samples, including: Laser marking is performed on the first surface of the first metal substrate to assist in positioning the grains; A second metal substrate is obtained by attaching a wire to the second surface of the first metal substrate after marking; the first surface and the second surface are opposite to each other. The second metal substrate is cold-embedded using resin and curing agent; The embedded second metal substrate is ground and polished to remove the oxide layer and deformation layer on the surface of the metal substrate; A metal sample is obtained by surface sputtering gold onto the second metal substrate after grinding and polishing.

4. The in-situ electroplasticity testing method according to claim 3, characterized in that, Pressing the pressure head onto the micropillar structure includes: The indenter is installed on the fine adjustment stage of the in-situ testing equipment, and the metal sample is fixed on the displacement stage of the in-situ testing equipment. The in-situ testing equipment is installed inside the scanning electron microscope. One pole of the pulse power supply is electrically connected to the wire attached to the metal sample, and the other pole is electrically connected to the pressure head. The displacement stage is controlled to move, thereby moving the micropillar structure of the metal sample below the indenter; The fine adjustment stage is controlled to move, pressing the pressure head onto the micro-column structure to generate prestress.

5. The in-situ electroplasticity testing method according to claim 4, characterized in that, The prestress ranges from 0.3mN to 0.5mN.

6. The in-situ electroplasticity testing method according to claim 4, characterized in that, The in-situ testing equipment is electrically connected to the scanning electron microscope, and the in-situ testing equipment has the same reference potential as the scanning electron microscope.

7. The in-situ electroplasticity testing method according to claim 3, characterized in that, The preparation of metal samples also includes: Based on electron backscatter diffraction, the grain orientation and morphology information of the metal sample are obtained; Based on the grain orientation and morphology information, the metal sample is placed in a scanning electron microscope, and the micropillar structure is obtained by cutting the metal sample using a polyion beam.

8. The in-situ electroplasticity testing method according to claim 7, characterized in that, The process of cutting the metal sample to obtain the micropillar structure includes: Select a center position, and cut an annular pattern with an inner diameter of 12μm and an outer diameter of 35μm based on the center position, and remove the material around the outer diameter; At the central position, continue cutting to obtain a microcylinder preform with a diameter of 6.5 μm and a height of 5 μm; Based on the central position, an annular pattern with an inner diameter of 6μm and an outer diameter of 20μm is cut to obtain a metal structure with a diameter of 5μm and a height of 10μm.

9. The in-situ electroplasticity testing method according to claim 8, characterized in that, The process of cutting the metal sample to obtain the micropillar structure further includes: Fine finishing of a metal structure with a diameter of 5μm and a height of 10μm.

10. An in-situ electroplasticity testing device, characterized in that, include: Scanning electron microscope; An in-situ testing device is installed inside the scanning electron microscope. The in-situ testing device includes a fine adjustment stage, an indenter and a displacement stage installed on the fine adjustment stage; the metal sample includes a micropillar structure, and the displacement stage is used to move the metal sample so that the micropillar structure is moved below the indenter; a pulse power supply has one pole electrically connected to the metal sample and the other pole electrically connected to the indenter. The fine adjustment stage is used to move the pressure head so that the pressure head presses against the micro-column structure; The first controller is electrically connected to the scanning electron microscope; The second controller is electrically connected to the in-situ testing equipment; the third controller is electrically connected to the pulse power supply; the third controller is used to regulate the output current of the pulse power supply; the second controller is used to control the displacement stage, move the metal sample through the displacement stage, and control the fine adjustment stage to move the indenter, so as to regulate the stress of the indenter on the micro-pillar structure, so as to cause the micro-pillar structure to undergo plastic deformation. The first controller is used to control the scanning electron microscope to record the plastic deformation process of the micropillar structure and obtain the correspondence between output current, stress and deformation.

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