Microscopic characterization method for microstructure performance

Abstract

The invention provides a microscopic characterization method for microscopic structure performance. The microscopic characterization method specifically comprises the following steps: S1, determining and selecting a microscopic structure to be detected in a sample under a scanning electron microscope; s2, manufacturing a micro-column by using a focused ion beam: manufacturing a column body on the microscopic structure to be measured by using the focused ion beam, manufacturing a pit around the column body, then gradually reducing the beam current of the focused ion beam to finely etch the column body, and finally obtaining the micro-column meeting the preset size requirement; s3, after the micro-column is manufactured, putting a sample into a nanoindenter, and performing a nanoindentation test by adopting a continuous rigidity measurement method to obtain a load-displacement curve of the micro-column; and S4, converting the load-displacement curve into a stress-strain curve by taking the upper cross section of the micro-column as a stress area and taking the ratio of the displacement change of the micro-column to the height of the micro-column as strain. According to the technical scheme, the technical blank that the performance of a microscopic structure in a certain form cannot be measured independently is filled.

Description

Technical Field

[0001] The present invention relates to the technical field of material analysis and testing, and in particular to a microscopic characterization method for microstructure performance. Background Art

[0002] The microstructures vary in morphology, and their properties vary accordingly. For example, bainitic steel is widely used in pipelines, engineering machinery, pressure vessels, bridges, and other fields due to its high strength, high toughness, and good weldability. Due to different controls on process parameters such as temperature, deformation, cooling rate, and welding, microstructures with different microscopic characteristics such as lathe bainite, granular bainite, and quasi polygonal bainite can be formed. Because of the continuity of bainite transformation, these different structures often exist in the sample at the same time; for example, the spacing between pearlite lamellae also has an important influence on the performance. However, it is difficult to obtain the relationship between the microstructure of a certain morphology in a certain micro-region, such as a pearlite structure with a single lamella spacing or a single morphology of bainite structure and performance in the prior art, so there is little research on the micro-region mechanical properties of interlamellar spacing or the micro-region mechanical properties of bainite single-phase structure. Summary of the invention

[0003] According to the above technical problems existing in the prior art, a microscopic characterization method of microstructure performance is provided, and a microcolumn body is produced by using focused ion analysis to study the structure and performance.

[0004] The technical means adopted by the present invention are as follows:

[0005] A microscopic characterization method for microstructural properties specifically comprises the following steps:

[0006] S1. Determine and select the microstructure to be tested in the sample under a scanning electron microscope;

[0007] S2. Fabrication of microcolumns using focused ion beam:

[0008] A column is made on the microstructure to be tested by using a focused ion beam and a pit is made around the column. Then the beam current of the focused ion beam is gradually reduced to finely etch the column, and finally a microcolumn that meets the preset size requirements is obtained.

[0009] S3. After the micro-pillar is fabricated, the sample is placed in a nanoindenter and a nanoindentation test is performed using a continuous stiffness measurement method to obtain a load-displacement curve of the micro-pillar;

[0010] S4. The load-displacement curve is converted into a stress-strain curve by taking the upper cross-section of the microcolumn as the load-bearing area and the ratio of the change in microcolumn displacement to the microcolumn height as the strain.

[0011] Furthermore, in step S1, the working parameters of the scanning electron microscope are: acceleration voltage 15-30 kV, working distance 5-10 mm, aperture 30-60 μm, magnification 1000-50000 times, and high-definition electron images are obtained when the scanning speed is greater than 28 seconds / frame.

[0012] Furthermore, in step S2, the diameter of the column is 10 μm, and the diameter of the pit is 25-30 μm; the diameter of the microcolumn does not exceed 5 μm, the height of the microcolumn is 2-3 times the diameter, and the microcolumn should be kept cylindrical as much as possible, with a taper not exceeding 5°.

[0013] Furthermore, in step S3, the load resolution of the nanoindentation test is above 1 nN, and the resonance frequency is 40-50 Hz; when performing the nanoindentation test, a Berkovich diamond indenter with a flat indenter with a side length of 10 μm is used, and the maximum indentation depth is pre-set to within 1500 nm, and then a continuous stiffness measurement method is used to obtain the load-displacement curve of the microcolumn.

[0014] Further, the microstructure includes but is not limited to bainite, pearlite, ferrite, martensite or austenite.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The microscopic characterization method of microstructural properties provided by the present invention utilizes a focused ion beam to produce microcolumns, and then uses a nanoindenter to continuously measure the microscopic properties of these columns. This method can be used to study microstructures and mechanical properties. This measurement method fills the gap that the microstructural properties of a certain morphology or region could not be measured separately in the past, and can be applied to detection and analysis practices in the future to improve research and development capabilities.

[0017] Based on the above reasons, the present invention can be widely promoted in the field of material analysis and testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0019] Figure 1 Schematic diagram of the fabrication process of the microcolumn of the present invention.

[0020] Figure 2 Schematic diagram of microcolumns fabricated on three forms of bainite in Example 1.

[0021] Figure 3 These are the stress-strain curves of three forms of bainite in Example 1.

[0022] Figure 4 Schematic diagram of pearlite with three different interlamellar spacings determined in Example 2.

[0023] Figure 5 (a)-(c) are schematic diagrams of microcolumns fabricated on pearlite with three different interlamellar spacings in Example 2.

[0024] Figure 6 These are the stress-strain curves of pearlite with three different interlamellar spacings in Example 2. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] like Figure 1 As shown, the present invention provides a microscopic characterization method for microstructural properties, which specifically includes the following steps:

[0027] S1. Determine and select the microstructure to be tested in the sample under a scanning electron microscope;

[0028] S2. Fabrication of microcolumns using focused ion beam:

[0029] A column is made on the microstructure to be tested by using a focused ion beam and a pit is made around the column. Then the beam current of the focused ion beam is gradually reduced to finely etch the column, and finally a microcolumn that meets the preset size requirements is obtained.

[0030] S3. After the micro-pillars are fabricated, the samples are placed in a nanoindenter and a nanoindentation test is performed using a continuous stiffness measurement method (CSM) to obtain the load-displacement curve of the micro-pillars.

[0031] S4. The load-displacement curve is converted into a stress-strain curve by taking the upper cross-section of the microcolumn as the load-bearing area and the ratio of the change in microcolumn displacement to the microcolumn height as the strain.

[0032] Furthermore, in step S1, the working parameters of the scanning electron microscope are: acceleration voltage 15-30 kV, working distance 5-10 mm, aperture 30-60 μm, magnification 1000-50000 times, and high-definition electron images are obtained when the scanning speed is greater than 28 seconds / frame.

[0033] Furthermore, in step S2, the diameter of the column is 10 μm, and the diameter of the pit is 25-30 μm; the diameter of the microcolumn does not exceed 5 μm, the height of the microcolumn is 2-3 times the diameter, and the microcolumn should be kept cylindrical as much as possible, with a taper not exceeding 5°.

[0034] Furthermore, in step S3, the load resolution of the nanoindentation test is above 1 nN, and the resonant frequency is 40-50 Hz; when performing the nanoindentation test, a Berkovich diamond indenter with a flat indenter with a side length of 10 μm is used, and the maximum indentation depth is pre-set to within 1500 nm, and then the continuous stiffness measurement method (CSM) is used to obtain the load-displacement curve of the microcolumn.

[0035] Furthermore, the microstructure includes but is not limited to bainite, pearlite, ferrite, martensite or austenite, etc.

[0036] Example 1

[0037] This embodiment takes low-carbon bainitic steel for pressure vessels as an example, and adopts the method of the present invention to perform microscopic characterization of bainite properties, which specifically includes the following steps:

[0038] S1. Determine and select the three forms of bainite in the bainitic steel sample under a scanning electron microscope, such as Figure 2 As shown;

[0039] The working parameters of the scanning electron microscope were: acceleration voltage 20 kV, working distance 10 mm, aperture 60 μm, magnification 3000 times, and high-definition electron images of bainitic steel were obtained at a scanning speed of 28 s / frame;

[0040] S2, such as Figure 2 As shown in the figure, focused ion beams were used to fabricate micropillars of the same size on three forms of bainite:

[0041] A 10μm diameter column was made on the bainite using a focused ion beam and a 30μm diameter pit was made around the column. Then the beam current of the focused ion beam was gradually reduced to finely etch the column, and finally a microcolumn with a diameter of 3μm and a height of 6μm was obtained.

[0042] S3. After the micro-pillars are fabricated, the bainite steel sample is placed in a nanoindenter and a nanoindentation test is performed using the continuous stiffness measurement method (CSM) to obtain the load-displacement curve of each micro-pillar;

[0043] The load resolution of the nanoindentation test is 1 nN, the resonance frequency is 45 Hz, and the Berkovich diamond indenter with a flat indenter with a side length of 10 μm is used for the nanoindentation test, and the maximum indentation depth is preset at 1000 nm;

[0044] S4. Taking the upper cross section of the microcolumn as the load-bearing area and the ratio of the change in microcolumn displacement to the microcolumn height as the strain, the load-displacement curve is converted into a stress-strain curve. The results are shown in Figure 3 shown.

[0045] Example 2

[0046] This embodiment takes heavy rail steel as an example, and adopts the method of the present invention to perform microscopic characterization of pearlite properties, which specifically includes the following steps:

[0047] S1. Determine and select pearlite with three different interlamellar spacings in the steel sample under a scanning electron microscope, such as Figure 4 As shown;

[0048] The operating parameters of the SEM were: accelerating voltage 25 kV, working distance 7 mm, aperture 30 μm, magnification 10,000 times, and high-definition electron images of the steel samples were obtained at a scanning speed greater than 28 s / frame;

[0049] S2, such as Figure 5 As shown in (a)-(c), micropillars of the same size were fabricated using focused ion beam on pearlite with three different interlamellar spacings:

[0050] A 10μm diameter column was made on the pearlite using a focused ion beam and a 30μm diameter pit was made around the column. The beam current of the focused ion beam was then gradually reduced to finely etch the column, ultimately obtaining a 3μm diameter and 6μm high microcolumn.

[0051] S3. After the micro-pillars are fabricated, the steel samples are placed in a nanoindenter and a nanoindentation test is performed using a continuous stiffness measurement method to obtain a load-displacement curve for each micro-pillar.

[0052] The load resolution of the nanoindentation test is 1 nN, the resonance frequency is 45 Hz, and the Berkovich diamond indenter with a flat indenter with a side length of 10 μm is used for the nanoindentation test, and the maximum indentation depth is preset at 1000 nm;

[0053] S4. Taking the upper cross section of the microcolumn as the load-bearing area and the ratio of the change in microcolumn displacement to the microcolumn height as the strain, the load-displacement curve is converted into a stress-strain curve. The results are shown in Figure 6 shown.

[0054] The microscopic characterization method of microstructure performance provided by the present invention utilizes a focused ion beam to produce microcolumns, and then uses a nanoindenter to continuously measure the microscopic properties of these columns. This method can be used to study microstructures and mechanical properties. This measurement method fills the gap that a certain microstructure performance could not be measured independently in the past, and can be applied to detection and analysis practices in the future to improve research and development capabilities.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A microscopic characterization method for microstructural properties, characterized in that: The specific steps include: S1. Determine and select the microstructure to be tested in the sample under a scanning electron microscope; S2. Fabrication of microcolumns using focused ion beam: A column is made on the microstructure to be tested by using a focused ion beam and a pit is made around the column. Then the beam current of the focused ion beam is gradually reduced to finely etch the column, and finally a microcolumn that meets the preset size requirements is obtained. S3. After the micro-pillar is fabricated, the sample is placed in a nanoindenter and a nanoindentation test is performed using a continuous stiffness measurement method to obtain a load-displacement curve of the micro-pillar; S4. The load-displacement curve is converted into a stress-strain curve by taking the upper cross-section of the microcolumn as the load-bearing area and the ratio of the change in microcolumn displacement to the microcolumn height as the strain.

2. The microscopic characterization method of microstructural properties according to claim 1, characterized in that: In step S1, the working parameters of the scanning electron microscope are: acceleration voltage 15-30 kV, working distance 5-10 mm, aperture 30-60 μm, magnification 1000-50000 times, and high-definition electron images are obtained when the scanning speed is greater than 28 seconds / frame.

3. The microscopic characterization method of microstructural properties according to claim 1, characterized in that: In step S2, the diameter of the column is 10 μm, and the diameter of the pit is 25-30 μm; the diameter of the microcolumn does not exceed 5 μm, and the height of the microcolumn is 2-3 times the diameter. The microcolumn should be cylindrical as much as possible, and the taper should not exceed 5°.

4. The microscopic characterization method of microstructural properties according to claim 1, characterized in that: In step S3, the load resolution of the nanoindentation test is above 1 nN, and the resonance frequency is 40-50 Hz; a Berkovich diamond indenter with a flat indenter with a side length of 10 μm is used in the nanoindentation test, and the maximum indentation depth is pre-set to be within 1500 nm, and then a continuous stiffness measurement method is used to obtain the load-displacement curve of the microcolumn.

5. The microscopic characterization method of microstructural properties according to claim 1, characterized in that: Microstructures include, but are not limited to, bainite, pearlite, ferrite, martensite or austenite.

Images