A micro-nano indentation testing device and testing method under extremely low temperature and strong magnetic field environment

Abstract

The invention relates to a micro-nano indentation testing device and a testing method under an extremely low temperature and strong magnetic field environment. The device is installed at the end of a sample rod of a liquid helium-free variable temperature superconducting magnet system and then inserted into a sample cavity. The customized liquid helium-free variable temperature superconducting magnet system provides a stable and adjustable extremely low temperature and strong magnetic field environment for the sample cavity. During the indentation test, the loading platform is controlled to be precisely driven to drive the tested sample to perform an indentation operation. The displacement of the indenter and the loading platform is measured respectively by a laser probe, so that the P-h curve in the indentation process can be obtained according to the testing method proposed by the invention, thereby realizing the testing and analysis of basic mechanical parameters such as hardness and elastic modulus of the tested sample under an extremely low temperature (10K-300K)-strong magnetic field (9T) environment. The invention will provide a novel means and tool for testing the service performance of materials under extreme environments and studying new physical properties, new phenomena and new laws under extremely low temperatures and strong magnetic fields.

Description

Technical Field

[0001] The present invention relates to the field of material mechanical property testing, specifically to testing using a precision instrument that integrates optics, mechanics, electricity, heat and magnetism, and more particularly to a micro-nano indentation testing device and testing method in an extremely low temperature and strong magnetic field environment. Background Art

[0002] In order to meet the requirements of mechanical equipment integration and lightweight, the size of materials is getting smaller and smaller, and the question of how to measure their mechanical properties is raised. Compared with traditional hardness testing methods, nanoindentation testing technology has many advantages such as accurate indentation depth, high measurement accuracy, and rich measured mechanical properties parameters. It has broad applications in superconducting materials, semiconductor materials, and thin film materials.

[0003] Under different service conditions, the mechanical properties of materials will vary greatly. With the development of aerospace, deep sea and polar exploration technology, the study of low temperature environment has gradually become an unavoidable difficulty and hot spot in research in recent years.

[0004] At the same time, for superconducting materials, extremely low temperatures are accompanied by a more severe strong magnetic field environment. High-tech equipment such as controlled nuclear fusion reactors, super high-speed rails, hadron colliders, ultra-high voltage transmission equipment, superconducting motors, superconducting submarines, electromagnetic catapults and super-energy electromagnetic guns all need to maintain normal working conditions in an extremely low temperature-strong magnetic field coupling environment, otherwise it will cause immeasurable losses to human society.

[0005] Therefore, there is an urgent need for a micro-nano indentation testing device and testing method under extremely low temperature and strong magnetic field environment, which is of great significance for testing the service performance of materials under extreme environments. Summary of the invention

[0006] The purpose of the present invention is to provide a micro-nano indentation testing device under an extremely low temperature and strong magnetic field environment, which is suitable for a liquid helium-free variable temperature superconducting magnet system, and can realize the testing and analysis of basic mechanical parameters such as hardness and elastic modulus of the tested sample under an extremely low temperature and strong magnetic field environment, and provide a novel means and tool for testing the service performance of materials under extreme environments and studying new physical properties, new phenomena and new laws under extremely low temperature and strong magnetic fields.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A micro-nano indentation test device in an extremely low temperature and strong magnetic field environment, the test device is installed in a sample cavity 18 of a liquid helium-free variable temperature superconducting magnet system, the upper end of the base bracket 1 is fixedly connected to a probe bracket 7, the probe bracket 7 is fixedly connected to a first laser probe 5 and a second laser probe 6, a fixed beam 8 is provided directly below the first laser probe 5, both ends of the fixed beam 8 are fixedly connected to the base bracket 1, a first reflector 4 is fixedly connected above the fixed beam 8, and a pressure head 9 is fixedly connected below the fixed beam 8; a point changing platform 15 is fixedly connected to the bottom of the base bracket 1 The point-changing platform 15 is fixedly connected to the pre-contact platform 13, driving the pre-contact platform 13 to move, the pre-contact platform 13 is fixedly connected to the loading platform 12, the loading platform 12 is fixedly connected to the sample table 11, and the sample table 11 is fixed with a test sample 10; the side of the loading platform 12 is fixedly connected to a displacement measuring plate 3, the displacement measuring plate 3 is fixedly connected to a second reflector 2, the second reflector 2 is located directly below the second laser probe 6, and the probe bracket 7 is fixedly connected to the end of the sample rod 16 and then inserted into the sample cavity 18 of the liquid helium-free variable temperature superconducting magnet system.

[0009] As a more optimal technical solution of the present invention, the liquid helium-free variable temperature superconducting magnet system is a single refrigerator as a cold source, and the cold head 22 of the refrigerator is installed above the vacuum shell 19 of the system; the cold shield 25 and the superconducting magnet 16 are respectively connected to the primary cold stage 24 and the secondary cold stage 26 of the cold head; the bottom of the sample cavity 18 is inserted into the superconducting magnet 16 and is concentric with the superconducting magnet 16; the helium circulation gas path providing variable temperature for the sample enters the cavity from the helium inlet 23 at the top of the vacuum cavity, and heat exchanges with the primary cold stage 24 and the secondary cold stage 26 inside, so that the helium is fully cooled, and the cooled helium passes through a manually adjustable needle valve and is throttled and cooled. After cooling, the colder helium is sprayed on the outer wall of the sample cavity 18 to cool the sample cavity 18. The sample cavity 18 is a static helium atmosphere, and the helium after heat exchange with the sample cavity rises along the interlayer outside the sample cavity 18, returns to the top of the vacuum cavity, and is pumped out from the helium outlet 20.

[0010] As a more optimal technical solution of the present invention, the overall size of the testing device is 40mm×34mm×128mm.

[0011] As a more optimal technical solution of the present invention, the switching platform 15 is fixedly connected to the adapter plate 14 , and the adapter plate 14 is fixedly connected to the pre-contact platform 13 .

[0012] As a more optimal technical solution of the present invention, the loading platform 12, the pre-contact platform 13 and the point-changing platform 15 are all piezoelectrically driven.

[0013] As a more optimal technical solution of the present invention, the base bracket 1, the displacement measurement plate 3, the probe bracket 7, the sample table 11 and the adapter plate 14 are made of 7075Al aluminum alloy.

[0014] As a more optimal technical solution of the present invention, the fixed beams 8 at both ends are made of TC4 titanium alloy.

[0015] As a more optimal technical solution of the present invention, the pressure head 9 is made of a non-magnetic stainless steel handle and a diamond tip.

[0016] As a more optimal technical solution of the present invention, the first reflector 4 and the second reflector 2 are made of single crystal silicon wafers, and the main parts of the loading platform 12, the pre-contact platform 13 and the point-changing platform 15 are all made of non-magnetic titanium alloy.

[0017] As a more optimal technical solution of the present invention, the loading platform 12 and the pre-contact platform 13, and the pre-contact platform 13 and the adapter plate 14 are connected by hexagonal screws, and the screws are made of non-magnetic stainless steel and titanium alloy.

[0018] As a more optimal technical solution of the present invention, the power supply wires of the loading platform 12, the pre-contact platform 13, and the point-changing platform 15 are all made of pure copper, the temperature sensor wires are made of phosphor bronze, and the leads of the first laser probe 5 and the second laser probe 6 are made of vacuum optical fibers, which are respectively introduced and led out through the aviation plug and the vacuum flange at the top of the sample rod 16.

[0019] The above-mentioned 7075Al aluminum alloy, TC4 titanium alloy, non-magnetic stainless steel, diamond, non-magnetic titanium alloy, and single crystal silicon are not affected by strong magnetic fields, and their deformation amounts are small at low temperatures.

[0020] The present invention also provides an indentation test method under an extremely low temperature and strong magnetic field environment. The test method is implemented based on the above-mentioned test device. The test device is installed in a sample cavity 18 of a liquid helium-free variable temperature superconducting magnet system. The liquid helium-free variable temperature superconducting magnet system provides an extremely low temperature and strong magnetic field environment for the test method. The sample cavity 18 is located between superconducting magnets 16. The superconducting magnets 16 provide a strong magnetic field for it. Cooling helium is sprayed on the outer wall of the sample cavity 18 to provide it with an extremely low temperature. The specific steps are as follows: when the indenter 9 just contacts the test sample 10, the displacements of the first laser probe 5 and the second laser probe 6 are reset to zero; when the indenter 9 is pressed into the test sample 10, the displacement of the indenter 9 is measured by the first laser probe 5, and the displacement of the loading platform 12 is measured by the second laser probe 6. The indentation displacement is equal to the displacement of the loading platform 12 minus the displacement of the indenter 9. The indentation load is equal to the stiffness of the fixed beams 8 at both ends multiplied by the indentation displacement, thereby obtaining a load-depth curve of the pressing process.

[0021] The beneficial effects are as follows:

[0022] The present invention provides a testing device and a testing method suitable for being placed in a sample cavity of a liquid helium-free variable temperature superconducting magnet system. The testing device and the testing method are highly accurate and interference-free, and can realize testing and analysis of basic mechanical parameters such as hardness and elastic modulus of the tested sample under extremely low temperature (10-300K) and strong magnetic field (9T) environments. The testing device and the testing method will provide novel means and tools for testing the service performance of materials under extreme environments and for studying new physical properties, new phenomena and new laws under extremely low temperatures and strong magnetic fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide further understanding of the present invention and constitute a part of this application. The illustrative examples of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 It is a schematic diagram of the overall structure of the testing device of the present invention;

[0025] Figure 2 The schematic diagram of the structure of the test device of the present invention installed on the liquid helium-free variable temperature superconducting magnet system (the dotted frame is the whole test device);

[0026] Figure 3 The schematic diagram of the testing method of the present invention is as follows: (a) when the indenter just contacts the tested sample; (b) when the indenter presses into the tested sample;

[0027] Figure 4 This is the schematic diagram of the indentation test under the action of variable temperature magnetic field.

[0028] In the figure: 1. base bracket; 2. second reflector; 3. displacement measuring plate; 4. first reflector; 5. first laser probe; 6. second laser probe; 7. probe bracket; 8. fixed beams at both ends; 9. pressure head; 10. tested sample; 11. sample table; 12. loading platform; 13. pre-contact platform; 14. adapter plate; 15. point change platform; 16. superconducting magnet; 17. sample rod; 18. sample cavity; 19. vacuum shell; 20. helium outlet; 21. mounting flange; 22. cold head; 23. helium inlet; 24. cold head first stage; 25. cold screen; 26. cold head second stage. DETAILED DESCRIPTION

[0029] The detailed content and specific implementation modes of the present invention are further described below in conjunction with the accompanying drawings.

[0030] See attached Figure 1 and attached Figure 2As shown, the present invention provides a micro-nano indentation testing device under an extremely low temperature and strong magnetic field environment. The testing device is installed in a sample cavity 18 of a liquid helium-free variable temperature superconducting magnet system. The overall size of the device is 40mm×34mm×128mm, including a base bracket 1, the upper end of the base bracket 1 is fixedly connected to a probe bracket 7, the probe bracket 7 is fixedly connected to a first laser probe 5 and a second laser probe 6, a fixed beam 8 is provided directly below the first laser probe 5, the two ends of the fixed beam 8 are fixedly connected to the side of the base bracket 1, and are compressed and fixed by hexagon socket screws and the probe bracket 7, a first reflector 4 is fixedly connected above the fixed beam 8, and a pressure head 9 is fixedly connected below the fixed beam 8; the first reflector 4 is glued to the upper surface of the middle part of the fixed beam 8 at both ends by low temperature glue, and the pressure head 9 is glued to the lower surface of the middle part of the fixed beam 8 at both ends by low temperature glue; a point changing platform 15 is fixedly connected to the bottom of the base bracket 1, and the point changing platform 15 is fixedly connected The pre-contact platform 13 drives the pre-contact platform 13 to move. The pre-contact platform 13 is fixedly connected to the loading platform 12. The loading platform 12 is fixedly connected to the sample platform 11. The sample platform 11 is fixed with a test sample 10 by low-temperature gluing. The sample platform 11 is installed on the loading platform 12 by hexagon socket screws. The test sample 10 is glued to the sample platform 11 by low-temperature gluing. The displacement measuring plate 3 is installed on the loading platform 12 by hexagon socket screws. The loading platform 12 is installed on the pre-contact platform 13 by hexagon socket screws. The side of the loading platform 12 is fixedly connected to the displacement measuring plate 3. The displacement measuring plate 3 is fixedly connected to the second reflector 2. The second reflector 2 is glued to the loading platform 12 by low-temperature gluing. The second reflector 2 is located directly below the second laser probe 6. The probe bracket 7 is fixedly connected to the end of the sample rod 17 and then inserted into the sample cavity 18 of the liquid helium-free variable temperature superconducting magnet system.

[0031] In some embodiments, the pre-contact platform 13 is installed on the change point platform 15 via an adapter plate 14 , the change point platform 15 is fixedly connected to the adapter plate 14 , and the pre-contact platform 13 is fixedly connected to the adapter plate 14 .

[0032] In some embodiments, the loading platform 12, the pre-contact platform 13 and the point-changing platform 15 are all piezoelectrically driven.

[0033] In some embodiments, the base support 1, the displacement measurement plate 3, the probe support 7, the sample table 11 and the adapter plate 14 are made of 7075Al aluminum alloy.

[0034] In some embodiments, the two end fixed beams 8 are made of TC4 titanium alloy.

[0035] In some embodiments, the indenter 9 is made of a non-magnetic stainless steel handle and a diamond tip.

[0036] In some embodiments, the first reflector 4 and the second reflector 2 are made of single crystal silicon wafers, and the main parts of the loading platform 12, the pre-contact platform 13, and the point-changing platform 15 are all made of non-magnetic titanium alloy.

[0037] In some embodiments, the loading platform 12 and the pre-contact platform 13, and the pre-contact platform 13 and the adapter plate 14 are all connected by hexagonal screws, and the screws are made of non-magnetic stainless steel and titanium alloy.

[0038] In some embodiments, the power supply wires of the loading platform 12, the pre-contact platform 13, and the point-changing platform 15 are all made of pure copper, the temperature sensor wires are made of phosphor bronze, and the leads of the first laser probe 5 and the second laser probe 6 are made of vacuum optical fibers, which are respectively introduced and led out through the aviation plug and the vacuum flange at the top of the sample rod 16.

[0039] In order to prevent the energized wires from cutting the magnetic flux lines and causing interference to the test signals during the test, the electrical test signal wires are electromagnetically shielded by using twisted pair cables plus a shielding layer.

[0040] In order to ensure that the heat load of the micro-nano indentation test device designed by the present invention meets the requirements, the necessary low-temperature heat distribution calculation is performed on the test device, which specifically includes the following steps:

[0041] 1. Heat conduction of sample rod (stainless steel, diameter 1.5cm, wall thickness 0.3mm, top spacing 1m)

[0042]

[0043] 2. Heat conduction of instrument leads (phosphor bronze, 4 leads, cross-sectional area 0.0127 mm2, length 2 m)

[0044]

[0045] 3. Heat input of current transmission leads (copper, 4 pairs, 2A current, cross-sectional area 0.8231mm2, length 2m)

[0046]

[0047] 4. Heat input from radiation (from an aluminum sample holder with an area of ​​100 cm2 and a temperature of 20 K to a stainless steel wall at 4.2 K)

[0048]

[0049] When the temperature of the aluminum sample holder is 100K:

[0050]

[0051] The total heat input is 43mW+0.13mW+672mW+3.4mW=0.72W, so we choose the cooling rate to be 0.8W.

[0052] The static helium atmosphere in the sample chamber is atmospheric pressure (105Pa), and the helium conduction is in a fluid dynamics state, which is independent of pressure. Therefore, when the sample holder is at 20K, for helium with an intermediate temperature of about 12K, the average thermal conductivity is about 0.018W / (m·K). Without considering convection, the gas cooling rate is:

[0053]

[0054] For a sample temperature of 100 K and an average value of about 0.005 W / (m·K), the gas cooling rate will rise to approximately:

[0055]

[0056] All of the above meet the cooling rate requirements.

[0057] See attached Figure 2 As shown, before the ultra-low temperature-strong magnetic field micro-nano indentation test, a self-customized liquid helium-free variable temperature superconducting magnet system is used to provide a stable and adjustable ultra-low temperature-strong magnetic field environment for the sample chamber, wherein the superconducting magnet 16 provides a strong magnetic field for it, and the magnetic field strength is regulated by changing the loading current, and the cooling helium is sprayed on the outer wall of the sample chamber 18 to provide it with an ultra-low temperature, and the low temperature is regulated by a needle valve with an adjustable flow rate. The temperature sensor is built into the lower end of the sample rod, and the sample chamber is in a static helium atmosphere to ensure temperature uniformity; the test device is installed as a whole at the end of the sample rod 17 on the liquid helium-free variable temperature superconducting magnet system, and is inserted into the In the sample chamber 18, the liquid helium-free variable temperature superconducting magnet system uses a single refrigerator as a cold source, and the cold head 22 of the refrigerator is installed above the vacuum shell 19 of the system. The cold shield 25 and the superconducting magnet 16 are respectively connected to the primary cold stage 24 and the secondary cold stage 26 of the cold head. The bottom of the sample chamber 18 is inserted into the superconducting magnet 16 and is concentric with the superconducting magnet 16. The helium circulation gas path that provides variable temperature for the sample enters the chamber from the helium inlet 23 at the top of the vacuum chamber, and performs heat exchange with the primary cold stage 24 and the secondary cold stage 26 inside, so that the helium is fully cooled. The cooled helium passes through a manually adjustable needle valve and is throttled and cooled. After cooling, the colder helium is sprayed on the outer wall of the sample chamber 18, thereby cooling the sample chamber 18. The sample chamber 18 is a static helium atmosphere to ensure temperature uniformity. The helium gas after heat exchange with the sample cavity rises along the interlayer outside the sample cavity 18 , returns to the top of the vacuum cavity, and is then pumped out from the helium gas outlet 20 .

[0058] See attached Figure 3 As shown, in the indentation test, the pre-contact platform is controlled to drive the tested sample gradually close to the end of the indenter. When the first laser probe detects a sudden displacement change in the fixed beams at both ends, the forward drive is stopped, and the reverse drive is 2μm until the displacement value is zero. The point-changing platform is controlled to change points. At this time, the distance between the surface of the tested sample and the indenter is less than 2μm, and the pre-contact is completed. The loading platform is controlled to drive the tested sample to perform the indentation operation in the precision drive mode. The test method includes the following steps:

[0059] When the pressure head 9 just contacts the test sample 10, the displacements of the first laser probe 5 and the second laser probe 6 are reset to zero;

[0060] When the pressure head 9 is pressed into the test sample 10, the fixed beams 8 at both ends, i.e. the pressure head 9, move The closed-loop displacement of the loading platform 12 is measured by the first laser probe 5 of the laser interferometer with picometer accuracy. The indentation displacement is measured by the second laser probe 6. , indentation load in K e is the stiffness of the two-end fixed beam 8, measured by hanging a standard single hook weight. Therefore, the displacement of the two-end fixed beam 8, i.e., the pressure head 9, is obtained. d i , Loading platform 12 closed loop displacement d i and the rigidity of the fixed beam 8 at both ends K e , the indentation displacement can be extracted d and indentation load , and finally the load-depth during the pressing process is obtained curve.

[0061] See attached Figures 1 to 4As shown in the figure, the principle and specific working process of the whole test device are as follows: the end of the sample rod 17 which is integrally mounted on the liquid helium-free variable temperature superconducting magnet system is inserted into the sample cavity 18 through the mounting flange 21; when performing the ultra-low temperature-strong magnetic field nanoindentation test, the liquid helium-free variable temperature superconducting magnet system is started to provide a stable and adjustable ultra-low temperature-strong magnetic field environment for the sample cavity 18, wherein the superconducting magnet 16 provides a strong magnetic field for it, and the magnetic field strength is regulated by changing the loading current, and the cooling helium is sprayed on the outer wall of the sample cavity 18 to provide it with an ultra-low temperature, and the low temperature is regulated by the needle valve with adjustable flow, and the sample cavity 18 is in a static helium atmosphere to ensure temperature uniformity; the pre-connection is controlled The touch platform 13 drives the tested sample 10 to gradually approach the end of the indenter 9. When the first laser probe 5 detects a sudden displacement change in the fixed beams 8 at both ends, the forward drive is stopped, and the reverse drive is 2μm until the displacement value is zero. The point-changing platform 15 is controlled to change points. At this time, the distance between the surface of the tested sample 10 and the indenter 9 is less than 2μm, and the pre-contact is completed; the loading platform is controlled to drive the tested sample 10 to perform the pressing operation in the precision driving mode; the first laser probe 5 and the second laser probe 6 respectively measure the displacement of the fixed beams 8 (i.e., the indenter 9) at both ends and the loading platform 12, and the indentation displacement and indentation load can be extracted according to the test method; the point-changing platform 15 is controlled to change points on the tested sample 10.

[0062] The above test process is repeated for multiple tests, so as to achieve the test and analysis of basic mechanical parameters such as hardness and elastic modulus of the test samples under extremely low temperature (10K-300K) and strong magnetic field (9T) environment.

[0063] The present invention uses a single refrigerator as a cold source and helium as a cooling medium, which can effectively reduce the helium consumption in the test and save the test cost; at the same time, the sample cavity is in a static helium atmosphere, and the temperature uniformity is easier to ensure. The present invention has various loading forms, which can respectively realize the extremely low temperature, strong magnetic field, extremely low temperature-strong magnetic field coupling loading of the sample cavity, and multi-point indentation / scratch load loading of the tested sample.

[0064] The present invention adopts piezoelectricity as the driving mode of the loading, pre-contact and point-changing platforms, and adopts a laser interferometer and a laser probe as a displacement detection device. All components and leads in the micro-nano indentation test device are made of non-magnetic materials, and the deformation amount is small at low temperature. It can work stably for a long time in an extremely low temperature-strong magnetic field environment. At the same time, in order to avoid the interference of the test signal caused by the energized wire cutting the magnetic flux line during the test, the electrical test signal wire is electromagnetically shielded by a twisted pair cable plus a shielding layer.

[0065] The testing method proposed in the present invention can extract the indentation load through displacement measurement and obtain the load-depth Ph curve during the indentation process, which solves the problem that the indentation load is difficult to measure under the extremely low temperature and strong magnetic field environment. It will provide a novel means and tool for testing the service performance of materials in extreme environments and studying new physical properties, new phenomena and new laws under extremely low temperature and strong magnetic fields.

[0066] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0067] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0068] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A micro-nano indentation testing device in an extremely low temperature and strong magnetic field environment, characterized in that: It comprises a liquid helium-free variable temperature superconducting magnet system that provides an extremely low temperature and strong magnetic field environment. The test device is installed in a sample chamber (18) of the liquid helium-free variable temperature superconducting magnet system. The upper end of the base support (1) is fixedly connected to a probe support (7). The probe support (7) is fixedly connected to a first laser probe (5) and a second laser probe (6). A fixed beam (8) is provided directly below the first laser probe (5). Both ends of the fixed beam (8) are fixedly connected to the base support (1). A first reflector (4) is fixedly connected above the fixed beam (8). A pressure head (9) is fixedly connected below the fixed beam (8). A point changing platform (15) is fixedly connected to the bottom of the base support (1), and a pre-contact platform (13) is fixedly connected to the point changing platform (15) to drive the pre-contact platform (13) to move, and a loading platform (12) is fixedly connected to the pre-contact platform (13), and a sample table (11) is fixedly connected to the loading platform (12), and a test sample (10) is fixedly connected to the sample table (11); a displacement measuring plate (3) is fixedly connected to the side of the loading platform (12), and a second reflector (2) is fixedly connected to the displacement measuring plate (3), and the second reflector (2) is located directly below the second laser probe (6); the probe support (7) is fixedly connected to the end of the sample rod (17) and then inserted into the sample cavity (18) of the liquid helium-free variable temperature superconducting magnet system; The cold source of the liquid helium-free variable temperature superconducting magnet system is a single refrigerator, and the cold head (22) of the refrigerator is installed above the vacuum shell (19) of the system; the cold shield (25) and the superconducting magnet (16) are respectively connected to the first cold stage (24) and the second cold stage (26) of the cold head; the bottom of the sample chamber (18) is inserted into the superconducting magnet (16) and is concentric with the superconducting magnet (16); the helium circulation gas path enters the shell from the helium inlet (23) at the top of the vacuum shell (19), and heat exchanges with the first cold stage (24) and the second cold stage (26) inside. The cooled helium passes through a needle valve and is throttled and cooled. After cooling, the colder helium is sprayed on the outer wall of the sample chamber (18). The sample chamber (18) is in a static helium atmosphere. The helium after heat exchange with the sample chamber rises along the interlayer outside the sample chamber (18), returns to the top of the vacuum chamber, and is pumped out from the helium outlet (20).

2. The micro-nano indentation testing device in an extremely low temperature and strong magnetic field environment as claimed in claim 1, characterized in that: The overall size of the testing device is 40mm×34mm×128mm.

3. The micro-nano indentation testing device in an extremely low temperature and strong magnetic field environment as claimed in claim 1, characterized in that: The point-changing platform (15) is fixedly connected to an adapter plate (14), and the adapter plate (14) is fixedly connected to a pre-contact platform (13).

4. The micro-nano indentation testing device in an extremely low temperature and strong magnetic field environment as claimed in claim 1, characterized in that: The loading platform (12), the pre-contact platform (13) and the point-changing platform (15) are all piezoelectrically driven.

5. The micro-nano indentation testing device in an extremely low temperature and strong magnetic field environment as claimed in claim 1, characterized in that: The base support (1), the displacement measuring plate (3), the probe support (7), the sample table (11) and the adapter plate (14) are made of 7075Al aluminum alloy; the fixed beam (8) is made of TC4 titanium alloy.

6. The micro-nano indentation testing device in an extremely low temperature and strong magnetic field environment as claimed in claim 1, characterized in that: The pressure head (9) is made of a non-magnetic stainless steel handle and a diamond tip.

7. The micro-nano indentation testing device in an extremely low temperature and strong magnetic field environment as claimed in claim 1, characterized in that: The first reflector (4) and the second reflector (2) are made of single crystal silicon wafers, and the main parts of the loading platform (12), the pre-contact platform (13) and the point changing platform (15) are all made of non-magnetic titanium alloy.

8. The micro-nano indentation testing device in an extremely low temperature and strong magnetic field environment as claimed in claim 1, characterized in that: The power supply wires of the loading platform (12), the pre-contact platform (13), and the point changing platform (15) are all made of pure copper, the temperature sensor wires are made of phosphor bronze, and the leads of the first laser probe (5) and the second laser probe (6) are made of vacuum optical fibers, which are respectively introduced and led out through the aviation plug and the vacuum flange at the top of the sample rod (17).

9. An indentation test method in an extremely low temperature and strong magnetic field environment, characterized in that: The test method is implemented based on the test device as claimed in claim 1. The test device is installed in the sample chamber (18) of the liquid helium-free variable temperature superconducting magnet system. The liquid helium-free variable temperature superconducting magnet system provides an extremely low temperature and strong magnetic field environment for the test method. The sample chamber (18) is located between the superconducting magnets (16). The superconducting magnets (16) provide a strong magnetic field for it. Cooling helium is sprayed on the outer wall of the sample chamber (18) to provide it with an extremely low temperature. When the indenter (9) just contacts the tested sample (10), the displacements of the first laser probe (5) and the second laser probe (6) are reset to zero. When the indenter (9) is pressed into the tested sample (10), the displacement of the indenter (9) is measured by the first laser probe (5), and the displacement of the loading platform (12) is measured by the second laser probe (6). The indentation displacement is equal to the displacement of the loading platform (12) minus the displacement of the indenter (9). The indentation load is equal to the stiffness of the fixed beams (8) at both ends multiplied by the indentation displacement, thereby obtaining a load-depth curve of the pressing process.

Images