A method for hardness testing and quantitative characterization of millimeter-sized samples

Abstract

This invention relates to a quantitative characterization method for the microstructure of millimeter-sized samples, belonging to the field of material microstructure, and addresses the low accuracy of existing hardness testing for small-sized samples and the low accuracy of quantitative microstructure data analysis using the EBSD method. The method includes the following steps: embedding the sample to be tested in an inlay material, followed by grinding and mechanical polishing; using a wedge-shaped tool to peel the sample entirely from the inlay material along the sample-inlay interface; subjecting the peeled sample to light etching or electrolytic polishing; observing and determining the type and minimum size of the microstructure in the sample using a microscope; attaching the sample to a base; performing hardness testing; statistically analyzing the frequency of hardness values ​​at all test points according to hardness intervals, plotting a hardness-frequency distribution curve, and using the inflection points and indentation morphology of the curve to determine the corresponding actual microstructure type, thus determining the hardness interval or hardness threshold for each phase; and calculating the percentage content of each phase in the sample. This invention offers a simple method with high testing accuracy.

Description

Technical Field

[0001] This invention relates to the field of materials microstructure technology, and in particular to a method for quantitative characterization of tissues in millimeter-sized samples. Background Technology

[0002] Due to the diverse alloying elements and complex preparation methods, the morphology of BCC (Body-Cellular) structures in steel is irregular, making it difficult to distinguish or determine the microstructure type through ordinary corrosion, let alone quantitatively detect various BCC structures. Since the properties of steel materials are closely related to their microstructure content, many materials require quantitative detection of microstructure content. Therefore, there is a significant demand for a rapid, simple, and accurate method to measure various types of BCC structures.

[0003] Currently, there is a wealth of research on quantitative detection methods for BCC structures, mainly including two types. One method involves continuously developing new etching agents to make the BCC structure appear in different colors under color metallographic acquisition mode, while simultaneously acquiring black and white metallographic images. The two types of images are compared and analyzed, and then image analysis software is used to quantify each phase. The disadvantages of this method are that the operation process is relatively complex and requires certain experience; otherwise, it may lead to large measurement errors or even failure to measure. Furthermore, the staining agents are not universal, and different staining agents need to be developed for different materials, resulting in a narrow range of applications. The other method uses scanning electron microscopy (EBSD) technology to analyze the differences in image quality among the phases in the BCC structure and then perform quantitative analysis. However, due to the many factors affecting grayscale differences, the boundary definition in the contrast image becomes uncertain. Obviously, this method has a large error and cannot accurately determine the grayscale value range or the extreme values ​​corresponding to grayscale values ​​of different phases in the same structure.

[0004] Existing processes disclose methods for qualitatively determining the microstructure of BCC using hardness. However, these methods are not suitable for millimeter-sized samples. Millimeter-sized materials have always been a challenge in determining the micro-area mechanical properties of materials. Sample preparation typically involves inlaying before hardness and elastic modulus measurements. However, due to the influence of the periphery effect, the hardness and modulus of small-sized samples cannot be accurately measured. The smaller the sample size and the shallower the indentation depth, the greater the influence of the periphery effect, leading to larger measurement errors. Currently, when testing the hardness of small-sized samples, improper sample preparation, poor contact between the sample and the inlay material, and product deviations during the indenter insertion process often result in incorrect test results. These errors fail to accurately characterize the material's hardness and modulus, thus providing incorrect guidance for material process optimization and quality improvement. Therefore, providing a quantitative characterization method for the microstructure of small-sized samples to offer reliable data support for material research and development is an urgent problem to be solved. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a quantitative characterization method for tissues of millimeter-sized samples to solve one of the following technical problems: the existing hardness detection accuracy of small-sized samples is low; the existing staining method for corrosion analysis of the content of various tissues in BCC structure is complicated and has low accuracy; the existing EBSD method for quantitative analysis of tissues is based on gray scale differences, uncertain boundary determination, cumbersome data processing and low accuracy.

[0006] On the one hand, the present invention provides a method for quantitative tissue characterization of millimeter-sized samples, comprising the following steps: Step 1, Sample Preparation: The sample to be tested is embedded in the mounting material, and then ground and mechanically polished in sequence; the sample is completely removed from the mounting material along the interface between the sample and the mounting material using a wedge tool; the removed sample is lightly etched or electrolytically polished; the type and minimum size of the tissue in the sample are preliminarily observed and determined using a microscope; Step 2: Adhere the sample to the base; Step 3, Hardness Test: Based on the minimum tissue size determined in Step 1, set the test parameters and use a high-precision indentation tester to perform the hardness test. The test parameters include the spacing of two-dimensional equidistant test points, the number of test points, the size of the test area, and the indentation depth or load. Among them, the spacing of the test points is less than the minimum tissue size determined in Step 1, the indentation size is less than the minimum tissue size, and the test area covers all phase structures in the sample. Step 4, Data Processing: Count the frequency of hardness values ​​at all measuring points according to hardness range, plot the hardness-frequency distribution curve, and combine the inflection point of the curve with the indentation location morphology to find the corresponding actual microstructure type, and determine the hardness range or hardness threshold of each phase; divide the number of points falling within the hardness range by the total number of measuring points to obtain the percentage content of each phase in the sample.

[0007] Furthermore, in step 1, the sample is pre-fixed on the sample preparation platform using double-sided tape during the inlay process, and then the inlay material is applied to complete the inlay; the sample preparation platform has a flat surface.

[0008] Furthermore, in step 1, the two sides of the wedge-shaped tool meet to form a cutting edge, the thickness of which is less than 0.3 mm; the cutting edge is set at an angle, and the end of the cutting edge is a tip with a width of less than 1 mm.

[0009] Furthermore, the specific operation of peeling and removing in step 1 is as follows: align the tip of the wedge-shaped tool with the outer edge of the sample, press the tip into the interface between the sample and the inlay material by 0.6~1mm, apply force obliquely along the edge of the sample to partially separate the sample from the inlay material, and then move the blade along the edge of the sample until the sample is completely removed from the inlay material.

[0010] Furthermore, in step 2, hot melt glass adhesive is used to adhere the sample to the base.

[0011] Furthermore, the voltage for electropolishing is controlled at 10~40V, and the polishing time is 10-30s.

[0012] Furthermore, in step 2, the base is made of aluminum alloy.

[0013] Furthermore, in step 1, the microscope is a metallurgical microscope, a scanning electron microscope, or an atomic force microscope.

[0014] Furthermore, in step 3, the high-precision indentation testing equipment is a nano-indenter.

[0015] Furthermore, in step 4, when plotting the hardness-frequency distribution curve, the number of hardness intervals is 10 to 60.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: a) The tissue quantitative characterization method for millimeter-sized samples of the present invention reduces the influence of the periphery effect of the mounting material by using the method of embedding-peeling-adhesion to the base, which has high testing accuracy, small testing error, and avoids erroneous results due to improper operation during the embedding process.

[0017] (b) The method of this invention does not require the preparation of etchants for different materials, resulting in different colors of the tissue under a metallographic microscope for quantification. This reduces environmental pollution and the impact on operator health. Furthermore, it lowers reliance on personnel's corrosion experience, as the corrosion process is complex and improper timing can significantly reduce testing accuracy. This method does not require special etchants and is universally applicable to various types of materials.

[0018] c) The method of this invention does not require complex subsequent data processing. The EBSD method requires standardization of image quality data, followed by multi-peak fitting to determine the proportions of each phase. This process is cumbersome, and the more steps involved, the more factors introduce error, reducing test accuracy. Furthermore, EBSD primarily identifies different phases by measuring the grayscale differences of individual pixels in the image. For materials with small grayscale differences in certain BCC structures, this can lead to uncertainty in the boundary definitions in the contrast diagram. This is particularly problematic when quantifying strip-shaped morphologies or relatively small tissue structures, where this method clearly has a large error and cannot accurately determine the grayscale value range or extreme values ​​corresponding to different phases within the same tissue. The method of this invention classifies and quantifies different phases based on the actual measured hardness values, providing direct measurement results rather than indirect fitting results, thus yielding more accurate results. Additionally, the data processing method of this invention is simple and does not require extensive operator experience.

[0019] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0021] Figure 1 A macroscopic view of a wedge-shaped cutting tool; Figure 2 The sample after being peeled from the inlay material; Figure 3 The sample is attached to the base. Figure 4 The microstructure of the dual-phase steel in Example 1 is shown in the figure. Figure 5 This is a topographic image of the test area after the hardness test of the duplex steel in Example 1; Figure 6 The hardness statistical distribution curve of the test area of ​​the duplex steel in Example 1; Figure 7 This is a microstructure diagram of medium carbon steel from Example 2; Figure 8 This is a hardness mapping diagram of medium carbon steel in Example 2; Detailed Implementation The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0022] This invention provides a method for quantitative tissue characterization of millimeter-sized samples, comprising the following steps: Step 1, Sample Preparation: The sample to be tested is embedded in the mounting material, and then ground and mechanically polished in sequence; the sample is completely removed from the mounting material along the interface between the sample and the mounting material using a wedge tool; the removed sample is lightly etched or electrolytically polished to reveal the tissue morphology; the type and minimum tissue size of the tissue in the sample are preliminarily observed and determined using a microscope. Step 2: Adhere the sample to the base; Step 3, Hardness Test: Based on the minimum tissue size determined in Step 1, set the test parameters and use a high-precision indentation tester to perform the hardness test. The test parameters include the spacing of two-dimensional equidistant measuring points, the number of measuring points, the size of the test area, and the indentation depth or load. Among them, the spacing of the measuring points is less than the minimum tissue size determined in Step 1, the indentation size is less than the minimum tissue size, and the test area covers all phase tissues in the sample. Step 4, Data Processing: Count the frequency of hardness values ​​at all measuring points according to hardness range, plot the hardness-frequency distribution curve, and combine the inflection point of the curve with the indentation location morphology to find the corresponding actual microstructure type, and determine the hardness range or hardness threshold of each phase; divide the number of points falling within the hardness range by the total number of measuring points to obtain the percentage content of each phase in the sample.

[0023] Specifically, the mounting material in step 1 can be either hot or cold, depending on the temperature sensitivity of the sample to be tested. During the mounting process, double-sided tape is used to pre-fix the sample on the sample preparation platform before applying the mounting material to complete the mounting, so as to avoid the sample shifting during the mounting process and causing the surface to be tested to be non-coplanar with the surface of the mounting material.

[0024] Specifically, the sample preparation platform in step 1 has a flat surface. Preferably, the sample preparation platform is a flat glass plate.

[0025] Specifically, the wedge-shaped tool in step 1 is made of alloy steel; such as Figure 1 The image shows a macroscopic view of a wedge-shaped tool. The two sides of the wedge meet to form the cutting edge. Considering that excessive cutting edge thickness would require greater force during the tip insertion process and hinder separation of the sample from the mounting material, the cutting edge thickness is controlled to be less than 0.3 mm, for example, 0.1~0.25 mm (e.g., 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm). The cutting edge is angled, with a pointed tip. Considering that excessive tip width would hinder separation of the sample from the mounting material, the tip width is controlled to be less than 1 mm, for example, 0.4~0.9 mm (e.g., 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm). This design facilitates the embedding of the wedge into the boundary between the sample and the mounting material.

[0026] Specifically, the peeling and removal operation in step 1 is as follows: align the tip of the wedge-shaped tool with the outer edge of the sample, press the tip into the interface between the sample and the insert material by about 0.6~1mm, apply force obliquely along the edge of the sample to partially separate the sample from the insert material, and then move the blade along the edge of the sample until the sample is completely removed from the insert material.

[0027] Specifically, in step 1, the stripped sample is lightly etched to reveal the tissue. The etchant is a 4% nitric acid alcohol solution. If the etching time is too long, the surface roughness will be too large, which will affect the test results for samples with small tissue size or samples with a small indentation depth. Therefore, the etching time should be controlled to the extent that the tissue can be distinguished.

[0028] Specifically, the stripped sample was subjected to light corrosion to reveal the structure. In step 1, the abrasive paper used was 120#, 400#, 600#, and 1000# in successive grades. The mechanical polishing was performed using a diamond polishing agent with a particle size of less than 5μm.

[0029] Preferably, in step 1, the exfoliated sample is subjected to electrolytic polishing to visualize the tissue. The polishing solution is a 6% perchloric acid-alcohol solution. Considering that excessively high electrolytic polishing voltage leads to increased surface roughness and poor image quality, while too low a voltage fails to achieve the desired polishing effect, making tissue observation impossible, and excessively long polishing time results in high surface roughness, while too short a time fails to achieve the desired polishing effect and makes tissue observation impossible, this is particularly problematic for samples with small tissue sizes or shallow indentation depths, which can affect test results. Therefore, the electrolytic polishing voltage is controlled to be 10–40V, such as 10V, 20V, 30V, or 40V; and the polishing time is controlled to be 10–30s, such as 10s, 12s, 14s, 16s, 18s, 20s, 22s, 24s, 26s, 28s, or 30s. Electrolytic polishing removes the deformed layer from the mechanical grinding process, reducing the impact of sample preparation on test results and making the results more accurate.

[0030] Specifically, the exfoliated samples were electrolytically polished to reveal the microstructure, with abrasive paper grades of 120#, 400#, 600#, 1000#, and 2000# being used progressively; mechanical polishing was performed using diamond polishing agent with a particle size of less than 5μm.

[0031] Specifically, in step 2, considering the need for heat conduction in the base, the material of the base is controlled to be a material with good thermal conductivity, such as aluminum alloy. The external dimensions of the base meet the sample mounting requirements of the testing equipment.

[0032] Preferably, in step 2, the base is a cylinder.

[0033] Specifically, in step 2, hot melt glass adhesive is used to adhere the sample to the base. The specific operation steps are as follows: heat the base to 120~140℃ (e.g., 120℃, 130℃, 140℃), apply hot melt glass adhesive to the base, and observe the melting of the hot melt glass adhesive. If the hot melt glass adhesive melts immediately after contact with the base, move the adhesive stick on the base until the area of ​​the melted adhesive on the base is larger than the area of ​​the sample. After the adhesive is evenly spread, adhere the sample to the base, and then remove the base from the heating plate and place it on a high-temperature resistant cooling platform to cool to room temperature. Figure 2 The image shows a sample after being peeled from the inlay material; Figure 3 The sample is attached to the base.

[0034] Specifically, in step 1, the microscope is a metallurgical microscope, a scanning electron microscope, or an atomic force microscope.

[0035] Specifically, in step 3, the high-precision indentation test equipment is a nano-indenter.

[0036] Specifically, in step 3, the spacing between adjacent measuring points in the two-dimensional direction is equal; the test area can be set to multiple different locations; the test mode is selected to control the indentation depth or control the load; the indenter used is a triangular pyramid Berkovich indenter; the indentation depth is more than 30 nm.

[0037] Specifically, in step 3, the maximum measurement interval should ensure that at least one point can be measured for each tissue unit. That is, the measurement interval should be smaller than the minimum tissue size, and the indentation size should be smaller than the minimum tissue size for each phase. The smaller the test interval, the higher the accuracy of the test results. Simultaneously, the minimum test interval size should be larger than the indentation size to ensure that two indentation points do not overlap and have a certain distance between them. The test can be conducted by controlling the indentation depth or the load. A larger test area yields more representative test results. Depending on the testing needs, to balance testing efficiency and accuracy, the measurement area should cover all types of tissues, and the test area size for each type of tissue should be larger than its minimum tissue size.

[0038] Specifically, in step 4, after the indentation test is completed, the morphology of the microstructure at the corresponding indentation location is observed, and the average hardness of each type of microstructure is estimated. Then, data analysis software is used to classify and process the data, analyzing the number of points or frequencies of hardness occurrences within different hardness ranges. The software is then used to plot the correlation curve between hardness and its frequency. If the curve has an inflection point, the hardness range of each phase is determined based on the inflection point and the estimated average hardness of each type of microstructure. If there is no obvious inflection point, the hardness range of each type of microstructure needs to be determined by combining the microstructure at the corresponding indentation location after the hardness test. Finally, the hardness range or threshold of each phase is determined, and the percentage content of that phase is obtained by dividing the total number of points distributed across different hardness ranges by the total number of measurement points.

[0039] Specifically, in step 4, when plotting the hardness-frequency distribution curve, the number of hardness intervals is 10 to 60; the number of inflection points of the curve is the same as the number of tissue types in the sample; when the curve has no obvious inflection points, the hardness range of each phase is determined by combining the tissue morphology at the corresponding position of the indentation.

[0040] Specifically, in step 4, a classification and clustering algorithm is used to classify the various tissues, and image processing software is used to calculate the percentage content of each phase. The specific method of the classification and clustering algorithm includes: after the test is completed, the number of phase types is set in the software according to the types of phases contained in the material. The software automatically classifies the phases according to their types and calculates the percentage content of each phase based on its hardness range. Specifically, the above method is applicable to the quantitative characterization of body-centered cubic multiphase microstructures of steel materials containing at least one of the phases of ferrite, bainite, and martensite. It can also be used for high-precision determination of the hardness and elastic modulus of a single microstructure in millimeter-scale wires, thin plates, and ring-shaped parts.

[0041] The advantages of the precise control of the method of the present invention are demonstrated below with specific embodiments and comparative examples.

[0042] Example 1 This embodiment provides a method for quantitative characterization of the microstructure of millimeter-sized samples. The sample in this embodiment is a duplex steel plate, and the composition of the duplex steel plate, by mass percentage, is: C: 0.0013%, Mn: 0.1%, Ti: 0.058%, S: 0.002%, with the balance being iron and unavoidable trace impurities. The thickness of the duplex steel plate is 1 mm, and the microstructure of the duplex steel plate is a ferrite and martensite dual-phase structure.

[0043] The method in this embodiment includes the following steps: (1) Sampling and mounting: Cut the sample into 5mm×5mm×1mm pieces using wire cutting; take a flat glass plate as a sample preparation platform, fix one side of double-sided tape to the glass, fix the sample on the other side of the double-sided tape and press it firmly; add mounting material and dental tray water for cold mounting, the mounting material is dental tray powder; (2) Grinding and peeling: Grind the sample step by step with 120#, 400#, 600#, 1000# and 2000# sandpaper, and then mechanically polish it with 5μm diamond polishing agent; use a wedge-shaped tool with a blade of about 0.1mm to completely peel the sample from the inlay; when peeling, align the tip of the tool with the outer edge of the sample, press the tip in about 1 mm, and then apply force obliquely along the edge of the sample to partially separate the sample from the inlay, and then move the blade along the edge of the sample until it is completely peeled off; the width of the tip of the blade is 0.5mm; (3) Electrolytic polishing: The stripped sample is electrolytically polished with a polishing voltage of 25V and a polishing solution of 6% perchloric acid alcohol solution. The polishing time is 15s. After electrolysis, the sample is immediately rinsed with water and dried with a hair dryer. (4) Tissue observation: The sample surface was scanned using an atomic force microscope, and the results are shown in the attached figure. Figure 4 As shown, the microstructure mainly consists of two phases: ferrite and martensite, with the minimum microstructure size of each phase generally greater than 2.5 μm; therefore, the interval was set to 1 μm when performing hardness mapping tests. (5) Adhesion: The aluminum alloy base is a cylinder with a height of 20mm and a diameter of 30mm. The base is heated to 130℃, and then hot melt glass glue is applied to the upper surface of the base. After the glue melts, the sample is adhered to the base. Then the base is removed from the heating plate and cooled to room temperature for hardness and elastic modulus determination. (6) Hardness Mapping Test: A Berkovich pyramidal indenter was used in load-controlled mode with a load set to 2 mN. Preliminary tests showed that the indentation size under this load was less than 1 μm, meeting the requirements that the indentations do not overlap and are smaller than the minimum tissue size. The test area was 100 μm × 100 μm, with a measurement point spacing of 1 μm, for a total of 10,000 measurement points. Due to the small indentation size, the morphology of the indentations was observed using a scanning electron microscope. The indentations were arranged at equal intervals in the two-dimensional direction. The results are shown in the attached figure. Figure 5 As shown, the hardness at all valid measuring points basically falls between 2.3 and 5.5 GPa; this is because the hardness results will differ due to the different orientations of the duplex steel. (7) Data processing: Frequency statistics were performed using Excel software according to the hardness range of 0.1 GPa, with a total of 32 ranges; a hardness-frequency distribution curve was plotted (see attached). Figure 6 As shown in the figure), by combining the indentation location morphology with the analysis, it can be seen that the hardness of ferrite is about 3 GPa and the hardness of martensite is about 4 GPa; the curve shows a clear inflection point at 3.5 GPa; since the hardness of martensite is higher than that of ferrite, the measuring points with a hardness less than 3.5 GPa are identified as ferrite, and the measuring points with a hardness greater than 3.5 GPa are identified as martensite; the ferrite content is statistically determined to be 44.43% and the martensite content is 55.57%.

[0044] The samples in this embodiment were tested using the existing 4% nitric acid alcohol etching method. Based on the different morphologies and colors of martensite and ferrite, the ferrite content was measured to be 41.6% and the martensite content to be 58.4%. It is evident that the method in this embodiment has high accuracy.

[0045] Example 2 This embodiment provides a method for quantitative characterization of the microstructure of millimeter-sized samples. The sample in this embodiment is a medium carbon steel plate, and the composition of the medium carbon steel plate, by mass percentage, is: C: 0.42%, Si: 0.23%, Mn: 0.66%, Cr: 1.01%, Mo: 0.16%, with the balance being iron and unavoidable trace impurities. The thickness of the medium carbon steel plate is 4 mm, and the microstructure of the medium carbon steel plate is a three-phase structure of pearlite, bainite, and martensite.

[0046] The method in this embodiment includes the following steps: (1) Sampling: Cut the sample into 5mm×5mm×1mm pieces by wire cutting; take a flat glass plate as a sample preparation platform, fix one side of double-sided tape to the glass, fix the sample on the other side of double-sided tape and press it firmly; add inlay material and dental tray water for cold inlay, the inlay material is dental tray powder; (2) After grinding with 120#, 400#, 600# and 1000# sandpaper in sequence, the sample was mechanically polished with 5μm diamond polishing liquid until there were no obvious scratches on the surface; the sample was completely peeled off from the inlay material using a wedge-shaped tool with a blade of about 0.1mm, as described in Example 1. (3) Corrosion revealing the tissue: Corrosion was performed with a 4% (v / v) nitric acid alcohol solution for 1 second, followed by immediate rinsing with water and drying; the tissue morphology was observed using a metallographic microscope, and the results are shown in the appendix. Figure 7 As shown, the minimum microstructure size of each phase is generally greater than 7 μm; (4) Adhesion: The sample is adhered to a base with a diameter of 30 mm and a height of 20 mm, in the same manner as in Example 1; (5) Hardness Mapping Test: A Berkovich triangular pyramid indenter was used in load control mode. The load was set to 2mN, corresponding to an indentation size of less than 1μm, ensuring that adjacent indentations did not overlap. The test area was 120μm×120μm, with a measuring point spacing of 1.2μm, arranged in a 100×100 grid, for a total of 10,000 measuring points. After the test, a hardness mapping diagram was generated as shown in the attached figure. Figure 8 As shown, the hardness at most of the measuring points falls between 2 and 7 GPa; (6) Data processing: The phases in the figure were classified and clustered according to the classification and clustering method. The material phases were set to three types, corresponding to pearlite, bainite and martensite. It can be seen that the average hardness of pearlite is 3GPa, the average hardness of bainite is about 4GPa, and the average hardness of martensite is about 6GPa. The software statistics show that the bainite content is 39.8%, the martensite content is 14.4%, and the rest is pearlite. The samples in this embodiment were tested using the existing 4% nitric acid alcohol etching method. Based on the different colors and morphologies of martensite and bainite, the bainite content was measured to be approximately 42%, and the martensite content was approximately 15.83%. It is evident that the method in this embodiment has high accuracy.

[0047] Extensive research was conducted during the study process, and some suboptimal solutions are presented here as comparative examples.

[0048] Comparative Example 1 This comparative example provides a method for quantitative characterization of tissue samples with millimeter-sized dimensions. The sample in this comparative example is the same as that in Example 1.

[0049] The method for this comparative example includes the following steps: (1) Same as (1) in Example 1; (2) Grinding and polishing: Grind step by step with 120#, 400#, 600#, 1000# and 2000# sandpaper, and then mechanically polish with 5μm diamond polishing agent; (3) Etching: The mounted specimen was etched with 4% nitric acid alcohol to reveal the morphology; after etching, the specimen was immediately rinsed with water and dried with a hair dryer. (4) Tissue observation: The sample surface was scanned using an atomic force microscope, and several ferrite tissue sites were marked. (5) Hardness test: The Berkovich triangular pyramid indenter was used in load control mode with the load set to 2mN. The hardness of the ferrite at the test mark was tested. A large number of bad spots were found, and no hardness test results were given or the results were greatly deviated. This indicates that the hardness test results are inaccurate. The analysis found that the sample and the insert were not in good contact. The indenter was deviated during the indentation process during the program execution, resulting in incorrect test results. The hardness of the material could not be accurately characterized and could not be used for quantitative characterization of the structure.

[0050] Comparative Example 2 This comparative example provides a method for quantitative characterization of tissue samples with millimeter-sized dimensions. The sample in this comparative example is the same as that in Example 1.

[0051] The method for this comparative example includes the following steps: (1) Same as (1) in Example 1; (2) Grinding and polishing: Grind step by step with 120#, 400#, 600#, 1000# and 2000# sandpaper, and then mechanically polish with 5μm diamond polishing agent; after mechanical polishing, use a hammer to break open the inlay material and take out the sample; (3) Electropolishing: The sample was electropolished at a voltage of 25V, and the polishing solution was a 6% perchloric acid alcohol solution. The polishing time was 5s. After electrolysis, the sample was immediately rinsed with water and dried with a hair dryer. (4) Tissue observation: The sample surface was scanned using an atomic force microscope, and several ferrite tissue sites were marked. (5) Adhesion: Same as (5) in Example 1; (6) Hardness test: A Berkovich triangular pyramid indenter was used in load control mode with a load set to 2 mN. The hardness of the ferrite at the test mark was measured, and the hardness at the test point fell between 1 and 14 GPa. This indicates that the hardness test results are inaccurate. Analysis revealed that the impaction process caused stress on some parts of the sample, which could not reflect the true hardness value of the material. Therefore, the hardness test results are inaccurate and cannot be used for precise quantitative characterization of microstructure.

[0052] Comparative Example 3 This comparative example provides a method for quantitative characterization of tissue samples with millimeter-sized dimensions. The sample in this comparative example is the same as that in Example 1.

[0053] The method for this comparative example includes the following steps: (1) Same as (1) in Example 1; (2) Same as (2) in Example 1; (3) is the same as (3) in Example 1; the difference is that the polishing time is 60s. (4) Tissue observation: The sample surface was scanned using an atomic force microscope, and several ferrite tissue sites were marked. (5) Adhesion: Same as (5) in Example 1; (6) Hardness test: A Berkovich triangular pyramid indenter was used in load control mode with a load set to 2 mN. The hardness of the ferrite at the test mark was measured, and the hardness at the test point fell between 0.5 and 15 GPa. This indicates that the hardness test results are inaccurate. Analysis revealed that the excessive polishing time increased the surface undulation, leading to test results that were either too high or too low, indicating that the hardness test results are inaccurate and cannot be used for quantitative characterization of tissues.

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for quantitative characterization of tissues in millimeter-sized samples, characterized in that, Includes the following steps: Step 1, Sample Preparation: The sample to be tested is embedded in the mounting material, and then ground and mechanically polished in sequence; the sample is completely removed from the mounting material along the interface between the sample and the mounting material using a wedge tool; the removed sample is lightly etched or electrolytically polished; the type and minimum size of the tissue in the sample are preliminarily observed and determined using a microscope; Step 2: Adhere the sample to the base; Step 3, Hardness Test: Based on the minimum tissue size determined in Step 1, set the test parameters and use a high-precision indentation tester to perform the hardness test. The test parameters include the spacing of two-dimensional equidistant test points, the number of test points, the size of the test area, and the indentation depth or load. Among them, the spacing of the test points is less than the minimum tissue size determined in Step 1, the indentation size is less than the minimum tissue size, and the test area covers all phase structures in the sample. Step 4, Data Processing: Count the frequency of hardness values ​​at all measuring points according to hardness range, plot the hardness-frequency distribution curve, and combine the inflection point of the curve with the indentation location morphology to find the corresponding actual microstructure type, and determine the hardness range or hardness threshold of each phase; divide the number of points falling within the hardness range by the total number of measuring points to obtain the percentage content of each phase in the sample.

2. The method for quantitative characterization of tissue samples at the millimeter scale according to claim 1, characterized in that, In step 1, the sample is pre-fixed on the sample preparation platform with double-sided tape during the inlay process, and then the inlay material is applied to complete the inlay; the sample preparation platform has a flat surface.

3. The method for quantitative tissue characterization of millimeter-sized samples according to claim 1, characterized in that, In step 1, the two sides of the wedge-shaped cutter meet to form a cutting edge, the thickness of which is less than 0.3 mm; the cutting edge is inclined, and the end of the cutting edge is a pointed tip with a width of less than 1 mm.

4. The method for quantitative characterization of tissue samples at the millimeter scale according to claim 3, characterized in that, The specific operation of peeling and removing in step 1 is as follows: align the tip of the wedge-shaped tool with the outer edge of the sample, press the tip into the interface between the sample and the inlay material by 0.6~1mm, apply force obliquely along the edge of the sample to partially separate the sample from the inlay material, and then move the blade along the edge of the sample until the sample is completely removed from the inlay material.

5. The method for quantitative tissue characterization of millimeter-sized samples according to claim 1, characterized in that, In step 2, hot melt glass adhesive is used to adhere the sample to the base.

6. The method for quantitative tissue characterization of millimeter-sized samples according to claim 1, characterized in that, The voltage for electropolishing is controlled at 10~40V, and the polishing time is 10-30s.

7. The method for quantitative characterization of tissue samples at the millimeter scale according to claim 1, characterized in that, In step 2, the base is made of aluminum alloy.

8. The method for quantitative tissue characterization of millimeter-sized samples according to claim 1, characterized in that, In step 1, the microscope is a metallurgical microscope, a scanning electron microscope, or an atomic force microscope.

9. The method for quantitative tissue characterization of millimeter-sized samples according to any one of claims 1 to 8, characterized in that, In step 3, the high-precision indentation testing equipment is a nano-indentation instrument.

10. The method for quantitative tissue characterization of millimeter-sized samples according to any one of claims 1 to 8, characterized in that, In step 4, when plotting the hardness-frequency distribution curve, the number of hardness intervals is 10 to 60.

Images