Micro / nano-scale indentation test method for high temperature yield strength of materials

Abstract

The application relates to a micro-nano scale indentation test method for high-temperature yield strength of materials, and belongs to the technical field of material strength test, which comprises the following steps: S1, fixing a sample to be tested on a sample table, and vacuumizing a sample bin; S2, temperature matching of the sample to be tested and a flat pressure head, so that thermal equilibrium is achieved between the flat pressure head and the sample to be tested; S3, indentation test of the sample to be tested by the flat pressure head, and obtaining a curve of displacement and load change with time; S4, non-parametric regression method is used to smooth the displacement load or displacement time curve, then the curve is differentiated, an analysis area is selected on the differentiated curve, and a segmented linear function is used for fitting to obtain a yield point, and yield strength of the sample is calculated according to the load of the yield point and the diameter of the flat pressure head. The method provided by the application can obtain yield strength at room temperature and above room temperature which is difficult to measure by conventional methods, and has high test precision and small uncertainty.

Description

Technical Field

[0001] This invention belongs to the field of material strength testing technology, specifically a micro-nano scale indentation test method for high-temperature yield strength of materials. Background Technology

[0002] Yield strength is an important parameter characterizing the mechanical properties of materials such as metals. Yield strength refers to the yield limit at which a material yields, that is, the stress that resists a small amount of plastic deformation. External forces exceeding this limit will cause permanent, irreversible deformation of the part.

[0003] The high-temperature yield strength of materials is usually obtained through tensile or compressive tests, and there are relatively well-established testing standards and equipment. However, conventional mechanical property testing has its limitations; it requires sampling and is a destructive test. Furthermore, for some samples such as thin films, coatings, heterogeneous surfaces of materials, and microdevices, it is difficult to obtain their high-temperature yield strength using conventional mechanical testing methods.

[0004] Nanoindentation is a commonly used method for testing the mechanical properties of materials at the micro- and nano-scale. Because the indentation depth is at the nanometer level, it can be considered a non-destructive measurement. Elastic modulus and hardness can be obtained from the indentation-unloading curve of a conical indenter, and relevant standards exist internationally and domestically. However, there is currently no reliable method for testing high-temperature yield strength using nanoindentation. When a cylindrical flat indenter is pressed into the sample, the load per unit surface area is equivalent to the load per unit cross-sectional area when the material begins plastic flow during a tensile test. The yield strength of the material can be obtained from the indentation curve. However, current data processing methods are easily affected by the surface roughness of the material. At high temperatures, indentation inevitably leads to a certain degree of thermal drift, which can severely affect the measurement results. Therefore, there is a need to find a high-temperature yield strength nanoindentation testing and data processing method with high measurement accuracy and small test result errors. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a micro-nano scale indentation test method for the high-temperature yield strength of materials. This method has high testing accuracy, low uncertainty, and is a non-destructive measurement method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A micro / nano-scale indentation test method for high-temperature yield strength of materials is characterized in that the method is implemented based on a high-temperature environment nano-indentation test device, which is equipped with a high-temperature resistant flat indenter, a water-cooled stage and a sample stage, and has a dual heating mode for the indenter and the sample; the device is installed inside a scanning electron microscope, which has a sample chamber, and the imaging function of the scanning electron microscope is used to select a suitable position for high-temperature indentation experiment.

[0008] The method includes the following steps:

[0009] S1. Fix the sample to be tested on the sample stage and evacuate the sample chamber;

[0010] S2. Perform temperature matching on the sample to be tested and the flat pressure head to achieve thermal equilibrium between the flat pressure head and the sample to be tested;

[0011] S3. The flat pressure head is used to perform an indentation test on the sample to be tested, and the curves of displacement and load change over time are obtained.

[0012] S4. The displacement and load curves obtained in step S3 are processed and analyzed to obtain the yield point, and the yield strength of the sample to be tested is calculated.

[0013] Furthermore, the micro / nano-scale indentation test method for the high-temperature yield strength of materials as described above includes the following steps before step S1:

[0014] The test area of ​​the sample to be tested is ground and polished to make the test surface flat and the surface roughness meet the experimental requirements.

[0015] Furthermore, in the micro-nano scale indentation test method for the high-temperature yield strength of materials as described above, the index for achieving thermal equilibrium between the flat indenter and the sample to be tested in step S2 is: the temperature of the flat indenter and the sample to be tested will not change after they come into contact.

[0016] Furthermore, in the micro-nano scale indentation test method for the high-temperature yield strength of materials as described above, the temperature matching method in step S2 is specifically as follows:

[0017] S21. Set the temperatures of the sample and the flat head to T respectively. s1 and T t1 Once the sample and the flat head have reached their respective stable temperatures, the PID controller will be turned off.

[0018] S22. After the temperature stabilizes or the temperature change becomes linear, conduct an indentation experiment to obtain the temperature-time curves of the sample and the flat indenter.

[0019] S23. For the temperature-time curve, select the interval where the temperature changes almost linearly before the sample and flat indenter come into contact, perform linear fitting, and use this as the temperature baseline. Obtain the maximum temperature change of the sample and flat indenter after subtracting the baseline, and denot them as d. Ts1 and d Tt1 ;

[0020] S24. Keep the sample temperature constant, i.e., T s2 =T s1 Change the temperature of the flat pressure head to T t2Repeat steps S21 to S23 to obtain the maximum temperature change values ​​of the sample and the flat head, respectively. Ts2 and d Tt2 ;

[0021] S25, Calculate the temperature T relative to the sample set temperature. s1 The temperature ΔT that needs to be changed for the matching flat pressure head t The calculation formula is:

[0022]

[0023] Furthermore, in the micro-nano scale indentation test method for the high temperature yield strength of materials as described above, each indentation test process in step S3 includes at least an indentation section, a load holding section, an unloading section, a thermal drift test section, and an indenter retraction section. The maximum load should ensure that the transition from the elastic segment to the elastoplastic segment can be clearly seen on the indentation curve.

[0024] Furthermore, in the micro-nano scale indentation test method for the high temperature yield strength of materials as described above, in step S3, another indentation point is selected on the sample, and the indentation test is repeated. Sufficient spacing should be maintained between the indentation points to ensure that they do not affect each other.

[0025] Furthermore, the micro-nano scale indentation test method for the high-temperature yield strength of materials as described above, the specific data processing and analysis method in step S4 includes the following steps:

[0026] S41. Use data processing software to perform preliminary processing on the raw data, including deducting load drift and thermal drift, deducting additional displacement caused by frame flexibility, and obtaining the time curve of load and displacement.

[0027] S42. Smooth the load-displacement curve or displacement-time curve, and then perform differentiation to obtain the displacement-time differential curve.

[0028] S43. The yield point is obtained by fitting the displacement differential curve with a piecewise linear function, and the load F at the yield point is then determined. c The yield strength σ of the sample is calculated from the diameter 'a' of the flat indenter. y,0.2 The calculation formula is:

[0029]

[0030] Furthermore, in the micro-nano scale indentation test method for the high-temperature yield strength of materials as described above, step S42 uses a non-parametric regression method to smooth the load-displacement curve or displacement-time curve.

[0031] Furthermore, in the micro-nano scale indentation test method for the high-temperature yield strength of materials as described above, the step S43, which involves fitting the displacement differential curve with a piecewise linear function to obtain the yield point, specifically involves:

[0032] An analysis region is selected on the displacement differential curve. The analysis region is divided into two segments: the first linear segment is close to a constant segment, and the second is a linearly rising segment. The intersection of the two segments is regarded as the inflection point, which is the yield point.

[0033] The micro-nano-scale indentation test method for high-temperature yield strength of materials described in this invention has the following significant technical advantages:

[0034] This invention is based on a high-temperature environment nano-indentation testing device. It uses a flat indenter to obtain indentation curves at different temperatures. After thermal drift correction, a bilinear function is applied to fit the load-displacement or displacement-time differential curve to obtain the yield point. Combined with the indenter size parameters, yield strength data at different temperatures are obtained. This method can obtain yield strengths at room temperature and above, which are difficult to measure using conventional methods for heterogeneous material surfaces, coatings, microelectromechanical systems (MEMS) components, etc. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a high-temperature environment nanoindentation testing device used in this invention;

[0036] Figure 2 This is a flowchart of a micro-nano scale indentation test method for high-temperature yield strength of materials provided in an embodiment of the present invention;

[0037] Figure 3a and 3b The figures show the load-time curve and displacement-time curve of a steel sample pressed in by a flat indenter at room temperature.

[0038] Figure 4 The pressure head indentation load-displacement curve of a steel sample at room temperature;

[0039] Figure 5 The results of fitting the displacement differential curve with a piecewise linear function are applied.

[0040] Figure 6 This is the result of the room temperature yield strength test for a steel sample;

[0041] Figure 7 For temperature matching process load-time curves;

[0042] Figure 8 The temperature change curves of the sample and the indenter over time during a single temperature matching process;

[0043] Figure 9 The load-displacement curves of a steel sample before irradiation and after irradiation to 50 dpa, are obtained by pressing a flat indenter into the sample at 350°C.

[0044] Figure 10Typical displacement-time differential curves of a steel sample before irradiation and after irradiation to 50 dpa at 350℃ are shown. Detailed Implementation

[0045] The present invention will now be further described with reference to specific embodiments and the accompanying drawings.

[0046] To address the problems mentioned in the background art, this invention proposes a micro-nano scale indentation testing method for the high-temperature yield strength of materials, based on a high-temperature environment nano-indentation testing device. This method can obtain the yield strength at room temperature and above, which is difficult to measure using conventional methods for heterogeneous surface regions of materials, as well as for coatings, microelectromechanical systems (MEMS) components. This method offers high testing accuracy, low uncertainty, and is a non-destructive measurement method.

[0047] Figure 1 This is a schematic diagram of a high-temperature environment nanoindentation testing device used in this invention. The device is equipped with a high-temperature resistant flat indenter and a water-cooled stage, and features dual heating modes for both the indenter and the sample. The device exhibits strong high-temperature testing stability. During the indentation experiment, the device is installed inside a scanning electron microscope (SEM). The SEM has a sample chamber, and the imaging function of the SEM is used to select a suitable location for the high-temperature indentation experiment.

[0048] Figure 2 This is a flowchart of a micro-nano scale indentation test method for high-temperature yield strength of a material provided in an embodiment of the present invention. The method includes the following steps:

[0049] S1. Fix the sample to be tested on the sample stage and evacuate the sample chamber.

[0050] The test area of ​​the sample should be flat and have low roughness, which can be achieved through grinding and polishing before testing. Fix the sample to be tested onto the sample stage using high-temperature adhesive or clamps, ensuring that the plane of the flat indenter in contact with the sample is parallel to the sample test surface. After fixing the sample, evacuate the sample chamber.

[0051] S2. Heat and temperature-match the sample and flathead to achieve thermal equilibrium between the flathead and the sample.

[0052] This step can be omitted if measuring room temperature yield strength.

[0053] Turn on the circulating water and use the aforementioned high-temperature nano-indentation testing device to heat the sample and indenter. After the temperature stabilizes, perform temperature matching between the sample and the indenter. The indicator of thermal equilibrium between the indenter and the sample is that their respective temperatures do not change after contact. Generally, a temperature drift minimization method is used for temperature matching, where the temperature change of the indenter is used as an indicator of the temperature difference between the sample and the indenter. The specific matching process is as follows:

[0054] S11. Set the temperatures of the sample and the indenter to T respectively. s1 and T t1 The two can differ by tens of degrees, where T s1 To test the temperature, the PID controller was turned off after the sample and the indenter reached their respective stable temperatures.

[0055] S12. After the temperature stabilizes or the temperature change becomes linear, perform an indentation experiment to obtain the temperature-time curves of the sample and the indenter.

[0056] When conducting the indentation experiment, a load control mode can be used to quickly (e.g., 10s) linearly load to between 100-200mN, hold the load for about 2 minutes, and then quickly (e.g., 10s) unload, obtaining the temperature-time curves of the sample and the indenter respectively.

[0057] S13. For the temperature-time curves in the above process, select the interval where the temperature changes almost linearly before the sample and indenter come into contact, perform linear fitting, and use this as the temperature baseline. Obtain the maximum temperature changes of the sample and indenter after subtracting the baseline, and denot them as d. Ts1 and d Tt1 ;

[0058] S14, The sample temperature remains constant, i.e., T s2 =T s1 Change the pressure head temperature to T t2 Repeating the above indentation experiment and data processing procedure, the maximum temperature changes of the sample and the indenter were obtained as d. Ts2 and d Tt2 ;

[0059] S15, Calculate the temperature T relative to the sample set temperature. s1 The matching pressure head needs to be changed at a temperature ΔT t The calculation method is as follows:

[0060] Plot the temperature difference between the sample and the indenter on the x-axis and the temperature change of the sample or indenter on the y-axis, respectively, with T... s1 -T t1 ,d Ts1 ) and (T s2 -T t2 ,d Ts2 (T) are two points, (T) s1 -T t1 ,d Tt1 ) and (T s2 -T t2 ,d Tt2 Draw two straight lines from two points, intersecting the horizontal axis at very close points. The average of these two intersection points is the temperature ΔT that the pressure head needs to change during temperature matching. t The calculation formula is:

[0061]

[0062] S3. Use a flat indenter to press the sample in, and obtain the curves of displacement and load changing over time.

[0063] Each indentation test process should include at least five segments: indentation, load holding, unloading, thermal drift testing, and indenter retraction. The maximum load should ensure a clear transition from the elastic to the elastoplastic phase on the indentation curve.

[0064] After step S3 is completed, other indentation points can be selected on the sample, and the indentation test can be repeated. Sufficient spacing should be maintained between the indentation points to ensure that they do not affect each other.

[0065] S4. Perform data processing and analysis on the displacement and load curves obtained in step S3 over time, and calculate the yield strength of the sample.

[0066] The specific data processing and analysis methods include the following steps:

[0067] S41. Use data processing software to perform preliminary processing on the raw data, including deducting load drift and thermal drift, deducting additional displacement caused by frame flexibility, and obtaining the time curve of load and displacement.

[0068] S42. Smooth the load-displacement curve or displacement-time curve, and then perform differentiation to obtain the displacement-time differential curve.

[0069] In the existing technology, there are several methods to extract the yield point from the load-displacement curve. One method depends on the selection of the zero point, but the zero point is not only related to the surface condition of the material, but also to the angle between the sample and the surface of the indenter, which has a significant impact on the measurement results. Another method is to differentiate the load-displacement curve and find the inflection point of the curve. The result does not depend on the zero point, but since the numerical calculation of the differentiation is easily affected by the noise of the experimental data, smoothing must be performed before differentiation.

[0070] This invention employs a nonparametric regression method to smooth the load-displacement or displacement-time curves. This method can effectively preserve information such as peak values ​​and inflection points while smoothing the curve. If the load loading rate is constant during the loading phase, the inflection point on the load-displacement curve dF / dh corresponds to the inflection point on the displacement-time curve dh / dt. Differentiating the smoothed load-displacement or displacement-time curves yields the displacement-time differential curve.

[0071] S43. The yield point is obtained by fitting the displacement differential curve with a piecewise linear function. The yield strength of the sample is then calculated from the load at the yield point and the diameter of the flat indenter. Specifically:

[0072] First, roughly select the region of interest (ROI) on the displacement differential curve. Divide the ROI into two segments. If the thermal drift is small, the first linear segment is close to a constant segment, and the second is a linearly increasing segment. The intersection of the two segments is considered the inflection point, i.e., the yield point, denoted as F. c In high-temperature microscale indentation tests, thermal drift is a key factor affecting the test results. For flat indentation tests of yield strength, even if thermal drift exists, or even if the first derivative of thermal drift is not zero, piecewise linear functions can still be used for analysis.

[0073] The yield strength σ of the sample y,0.2 The calculation formula is:

[0074]

[0075] Where 'a' is the diameter of the flat pressure head.

[0076] Example 1: Measurement of room temperature yield strength of steel

[0077] Before testing, the samples were mechanically ground and polished using sandpaper, with 600#, 800#, 1000#, 1500#, 2000#, and 3000# sandpaper used sequentially. Polishing employed a three-step method: first, polishing was performed sequentially with 3μm and 1μm diamond polishing slurries; second, polishing was performed with Al2O3 polishing slurry with a particle size of 0.05μm; and third, final polishing was performed with nano-silica to remove the hardened layer left from the previous two polishing steps.

[0078] The sample to be tested was fixed on the sample stage with high-strength adhesive and tested on the in-situ nanoindentation instrument of the scanning electron microscope. A cylindrical indenter with a diameter of 10.94 μm was used and the sample chamber of the scanning electron microscope was evacuated.

[0079] When testing at room temperature, the indenter and the sample are at the same temperature, so temperature matching is not required.

[0080] The indenter was pressed in at room temperature, with the maximum load set at 250 mN. During the indentation phase, the load rate was set to a constant, and during the thermal drift phase, the load was set to 10% of the maximum load. A total of 10 indentation experiments were conducted.

[0081] The raw data was initially processed using data processing software, including deducting load drift and thermal drift, and deducting additional displacements caused by frame compliance, to obtain load and displacement time curves. The load and displacement curves from the first measurement over time are shown below. Figure 3a and Figure 3b As shown, the load-displacement curve is shown in the figure. Figure 4 As shown.

[0082] Nonparametric regression methods were applied to smooth the displacement-time curve, and the displacement-time differential curve was calculated. The analysis region was roughly selected based on the load-displacement curve, and this region only included the near-elastic and elastoplastic segments, such as... Figure 5 As shown ( Figure 5 (Only one of the 10 sets of data is shown in the figure). A piecewise linear function is applied to fit the displacement differential curve, and the intersection of the two segments is denoted as F. c Yield strength σ y,0.2 Represented as:

[0083]

[0084] Where a = 10.94 μm.

[0085] The results of 10 indentation experiments are shown below Figure 6 As shown, the black horizontal line represents the measurement value of the traditional tensile test, and the gray area represents the relative error of less than 10%. The average value of the nanoindentation test result is 528±7MPa, while the value of the traditional tensile test is 517MPa, with a difference of 2.1%. The relative uncertainty of the nanoindentation test is 1.4%. Figure 6 The results given by the maximum slope method are also shown in the figure. The data processing method in this invention is closer to the measurement values ​​of traditional tensile tests.

[0086] Example 2: Measurement of High-Temperature Yield Strength of Heterogeneous Surface Regions of Materials

[0087] The material is a type of fast reactor steel. After mechanical polishing as in Example 1, the sample was cleaned with plasma to remove organic residues on the surface. After heavy ion irradiation, an irradiation damage zone was formed at a depth of 5 μm on the material surface. The peak dose was 50 dPa. The mechanical properties of the irradiated area differed from those of the substrate.

[0088] The sample to be tested was fixed onto the sample stage of the high-temperature nano-indentation device using high-temperature adhesive, and a vacuum was drawn to ~10. -4 Pa. A flat indenter with a diameter of Φ = 10.94 μm was used. The sample and indenter were heated, and after the system stabilized, temperature matching was performed on the sample and indenter. The load-time curve for temperature matching is shown in [Figure number missing]. Figure 7 As shown in the figure. During temperature matching, the sample temperature during the first indentation is 350℃, and the indenter temperature is ~315℃. The PID controllers for both sample and indenter temperature control are turned off during temperature matching, resulting in a sample temperature change curve during the indentation process. This allows us to obtain the temperature change value during the contact period between the indenter and sample. Following the same procedure, a second indentation is performed with a sample temperature of 350℃ and an indenter temperature of ~370℃, yielding the temperature change value corresponding to the second temperature difference point between the indenter and sample. The temperature corresponding to the indenter and sample temperature matching is calculated and set as the indenter temperature in the testing software. The temperature change curves of the sample and indenter over time during the temperature matching process are shown in the figure. Figure 8 As shown, the process is divided into four stages: Stage I is the temperature instability stage, Stage II is the temperature stabilization stage, Stage III is the sample and indenter contact stage, and Stage IV is the temperature recovery stage.

[0089] The high-temperature nano-indentation device was installed inside a scanning electron microscope (SEM). The SEM's imaging function was used to select suitable locations for high-temperature indentation experiments. The loading rate was set to 8 mN / s. The maximum loads for the unirradiated and irradiated areas were set to 240 mN and 360 mN, respectively, requiring 30 s and 45 s to reach the maximum load. The thermal drift test section was set to 10% of the maximum load. A total of 12 indentation experiments were conducted. Typical load-displacement curves are shown below. Figure 9 As shown.

[0090] The displacement-time curve is smoothed using a nonparametric regression method, and the time derivative of the displacement is calculated. A typical curve is shown below. Figure 10 As shown. Then, the displacement differential curve was fitted using the same piecewise linear function as in Example 1 to obtain the yield point, and the yield strength was calculated from the yield point load. The yield strengths of the unirradiated region and the irradiated region were 547±4 MPa and 633±7 MPa, respectively, with relative uncertainties of 0.7% and 1.1%, respectively.

[0091] This invention provides a micro / nano-scale indentation testing method for the high-temperature yield strength of materials. Based on a high-temperature environment nano-indentation testing device, it uses a flat indenter to obtain indentation curves at different temperatures. After thermal drift correction, a bilinear function is applied to fit the load-displacement or displacement-time differential curve to obtain the yield point. Combined with the indenter size parameters, yield strength data at different temperatures are obtained. This method can obtain the yield strength at room temperature and above room temperature in heterogeneous surface regions of materials, as well as in coatings, microelectromechanical systems (MEMS) components, which are difficult to measure using conventional methods. The measurement uncertainty is generally less than 2%.

[0092] The above embodiments are merely illustrative examples of the present invention. The present invention may also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of the present invention should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A method for micro- and nano-scale indentation testing of high temperature yield strength of materials, characterized in that, The method is based on a high-temperature environment nanoindentation testing device, which is configured with a high-temperature-resistant flat indenter, a water-cooled table and a sample table, and has a double-heating mode of the indenter and the sample; the device is installed in a scanning electron microscope, which has a sample chamber, and the imaging function of the scanning electron microscope is used to select a suitable position for high-temperature indentation experiment; The method comprises the following steps: S1, fixing the sample to be tested on the sample table, and vacuumizing the sample chamber; S2, temperature matching of the sample to be tested and the flat indenter, so that the flat indenter and the sample to be tested reach thermal equilibrium, and the index of thermal equilibrium is that the temperature of the flat indenter and the sample to be tested will not change after contact; the method of temperature matching is specifically: S21, set the temperature of the sample and the flat head to T s1 and T t1 After the sample and the flat head reach the stable temperature respectively, turn off the PID; S22, after the temperature is stable or the temperature change is linear, a pressure test is carried out, and the temperature-time curves of the sample and the flat indenter are obtained respectively; S23. For the temperature-time curve, select the interval where the temperature changes almost linearly before the sample and flat indenter come into contact, perform linear fitting, and use this as the temperature baseline. Obtain the maximum temperature change of the sample and flat indenter after subtracting the baseline, and denot them as d. Ts1 and d Tt1 ; S24, keeping the sample temperature unchanged, i.e. T s2 = T s1 , changing the temperature of the flat head to T t2 , repeating steps S21-S23, and obtaining the maximum values of the temperature changes of the sample and the flat head as d Ts2 and d Tt2 , respectively; S25, calculate the temperature difference ΔT required for the matching flat press head to change to the sample setting temperature T s1 Matching flat press head required temperature change ΔT t The calculation formula is: S3, using the flat indenter to perform indentation test on the sample to be tested, and obtaining the curves of displacement and load changing with time, each indentation test process at least includes indentation section, load holding section, unloading section, thermal drift test section and indenter retraction section, and the maximum load should ensure that the transition from elastic section to elastic-plastic section can be clearly seen on the indentation curve; S4, processing and analyzing the curves of displacement and load changing with time obtained in step S3 to obtain the yield point, and calculating the yield strength of the sample to be tested; the specific data processing and analysis method comprises the following steps: S41, applying data processing software to preliminarily process the original data, including deducting load drift and thermal drift, and deducting additional displacement caused by frame compliance, to obtain the time curves of load and displacement; S42, using non-parametric regression method to smooth the load-displacement curve or displacement-time curve, and then differentiating to obtain the displacement-time differential curve; S43, the yield point is obtained by fitting the displacement differential curve with a piecewise linear function, specifically: selecting an analysis area on the displacement differential curve, the analysis area is divided into two sections, the first linear section is close to a constant section, and the second is a linear rising section, the intersection point of the two sections is regarded as an inflection point, that is, the yield point; the yield strength σ c of the sample is calculated from the load F y,0.2 of the yield point and the diameter a of the flat pressure head, and the calculation formula is:

2. The method of micro- or nano-scale indentation testing of the high-temperature yield strength of a material according to claim 1, characterized in that Before step S1, it comprises: The test area of the sample to be tested is polished and polished to make the test plane flat and the surface roughness meet the experimental requirements.

3. The method of micro- or nano-scale indentation testing of the high-temperature yield strength of a material according to claim 2, characterized in that In step S3, another indentation point is selected on the sample, and the indentation test is repeated, and the distance between the indentation points should be sufficient to ensure that the indentation points do not affect each other.

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