CN110940686B - Method for calculating critical splitting stress of twin crystal through EBSD technology and Vickers hardness tester - Google Patents
Method for calculating critical splitting stress of twin crystal through EBSD technology and Vickers hardness tester Download PDFInfo
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Abstract
And calculating the critical cutting stress of the twin crystal by an EBSD technology and a Vickers hardness tester. The method mainly comprises the steps of carrying out geometric analysis and calculation on Vickers hardness indentations with different loads, and combining the EBSD calibration crystal orientation and the twin crystal function to finally obtain the critical slitting stress of the twin crystal. The method comprises the following steps: preparing an EBSD (Electron Back scattering) block sample, and ensuring the flatness of the surface of the sample through chemical wiping corrosion or mechanical vibration polishing; determining a certain area of the sample in a metallographic microscope and EBSD, and marking the position with Vickers hardness; then, carrying out hardness test on the region through Vickers hardness of different loads until twin crystals appear beside the hardness indentation under a certain load, and recording the diagonal size and hardness numerical value of the hardness indentation; and then calibrating the type of the twin crystal by using EBSD (Electron Back scattering), and finally calculating by combining hardness indentation geometric analysis under the load with Schmid factor calculation to further obtain the critical slitting stress of the twin crystal.
Description
Technical Field
The invention belongs to the field of material analysis, and particularly provides a method for calculating the critical slitting stress of twin crystals by an EBSD (electron back scattering) technology and a Vickers hardness tester.
Background
The Vickers hardness is that under a specified load, a diamond regular pyramid pressure head with an included angle of 136 degrees is pressed into the outer surface of a sample, the load is removed after the sample is kept for a certain time, the geometric relation of the indentation is obtained by measuring the length of the diagonal, the surface area of the indentation is calculated, and then the average pressure of the surface area of the indentation is calculated, and the pressure is the Vickers Hardness Value (HV) of the material.
Under a certain load, the Vickers hardness indenter is pressed into the surface of the material, so that the material is subjected to compressive stress, the material can deform, and the two main modes of deformation are dislocation slip and twinning. The slip of dislocations is mainly classified into two types: and (4) performing dislocation winding cutting and cutting. The twinning means that under the action of shearing stress, one part of the crystal makes relative shearing with respect to the other part of the crystal along a certain crystal plane and crystal direction, that is, the two parts of the crystal form mirror symmetry by taking the twin plane as a symmetrical plane.
As an important deformation mode, the research on the formation mechanism of twins is very important. In order to study the twin formation mechanism, the critical part stress of the twin must be known. At present, the critical cutting stress of different twin crystals is mainly measured by simulation of VPSC and the like and by experiment measurement of micro-cantilever compression and the like. The critical slitting stress value of the twin crystal simulated by the VPSC model cannot reflect the actual critical slitting stress. Although the experiments such as micro-cantilever compression and the like can accurately measure the critical cutting stress of twin crystals, the experiments need high-end and expensive instruments, and have high cost and low popularity. Therefore, it is difficult to find a practical, simple and convenient method for measuring the actual critical slicing stress of the twin crystal. Therefore, it is important to find a method for simply and conveniently measuring the critical splitting stress of the twin crystal.
Disclosure of Invention
The invention aims to provide a method for calculating the critical slicing stress of twin crystals by an EBSD technology and a Vickers hardness tester. The method is simple and effective, and can accurately obtain the critical cutting stress of the twin crystal.
The technical scheme of the invention is as follows:
the method for calculating the critical cutting stress of the twin crystal by the EBSD technology and the Vickers hardness tester is characterized in that: and (3) calculating the geometric relation of the indentations by using a Vickers hardness tester in combination with an EBSD technology to further obtain the critical slitting stress of the twin crystal: preparing an EBSD sample, determining a certain area of the sample in a metallographic microscope and the EBSD, and marking the position by using Vickers hardness; then, carrying out hardness test on the region through Vickers hardness of different loads until twin crystals appear beside the hardness indentation under a certain load, and recording the diagonal size and hardness numerical value of the hardness indentation; and then calibrating the type of the twin crystal by using EBSD (Electron Back scattering), and finally calculating by combining hardness indentation geometric analysis under the load with Schmid factor calculation to further obtain the critical slitting stress of the twin crystal.
The method for calculating the critical slitting stress of the twin crystal through the EBSD technology and the Vickers hardness tester is characterized by comprising the following specific steps of:
1) preparing an EBSD (Electron Back scattering) block sample, and ensuring the flatness of the surface of the sample through chemical wiping corrosion or mechanical vibration polishing;
2) marking a certain position on the surface of the sample by using Vickers hardness, and recording the original appearance and crystal orientation of the area by using a metallographic microscope, a scanning electron microscope and an EBSD (electron back scattering detector);
3) measuring the hardness of the area by a Vickers hardness tester, replacing loads (from 10g to 1000g) with different sizes until twin crystals appear beside the indentation under a certain load, and recording the diagonal size and hardness value of the indentation;
4) determining the orientation of the crystal where the indentation is located through EBSD, obtaining a component force direction leading to twin crystal formation according to the geometric relation of the indentation, and calculating the value of Schmid factor of the twin crystal under the component force by combining the crystal structure calibrated by the EBSD; the formation process of twin crystals can be observed in situ by combining the EBSD calibration crystal orientation function, the formation force for measuring the twin crystals is brought into the EBSD calibrated crystal structure, and the Schmid factor is calculated
5) And obtaining the stress size causing the twin crystal formation according to the geometrical relation of the indentation, and finally obtaining the critical cutting stress of the twin crystal by combining the calculation result of the Schmid factor.
Wherein, the step 1) can adopt any one of the following methods to treat the surface of the sample:
the method comprises the following steps:
(1) pre-grinding and polishing: pre-grinding with 150#, 320#, 800# and 2000# water sand paper, removing deep scratches, and mechanically polishing with SiO as polishing solution2Polishing the nano turbid liquid for 6-10 minutes to finally obtain a bright and traceless polished surface with a mirror surface effect;
(2) etching: gently and rapidly wiping the surface of the sample for 3-10 seconds by using cotton stained with acid until the surface of the sample becomes bright, washing the sample by using clean water and absolute ethyl alcohol in sequence, and finally drying and storing;
the second method comprises the following steps:
firstly, inlaying a sample on an inlaying machine, then using 150#, 320#, 800# and 2000# water sand paper to pre-grind in sequence, removing deeper scratches, and finally performing vibration polishing on an automatic polishing machine, wherein the polishing solution is SiO2Polishing the nano suspension for 0.5-1 hour to obtain a bright and traceless polished surface with a mirror surface effect.
The features of the invention are as follows:
1. the critical cutting stress of a twin crystal is calculated by an EBSD technology and a Vickers hardness tester, and the magnitude of certain twin crystal forming force can be accurately measured by adjusting the weight (10-1000g) of the Vickers hardness tester;
2. the orientation of the crystal where the indentation is located is measured through an EBSD technology, and the Schmid factor value of the twin crystal under the action of force can be calculated by combining the direction of the twin crystal forming force;
3. the method establishes an interchange relation model of the Vickers hardness numerical value and the critical slitting stress of the twin crystal by combining the EBSD technology with the geometrical relation of the Vickers hardness indentation, and can simply, conveniently and accurately measure the critical slitting stress of the twin crystal;
4. by means of the timing and constant-speed mechanical polishing method, surface materials can be gradually removed, the morphology of twin crystals can be gradually observed, the dimensional change of Vickers indentations can be gradually observed through a scanning electron microscope, and then a three-dimensional model formed by the twin crystals can be obtained according to the geometric relation of the Vickers hardness indentations and the morphology of the twin crystals.
The related technical principle is as follows:
FIG. 1 is a three-dimensional schematic view of a Vickers hardness indenter. The solving principle of calculating the critical breaking stress of the twin crystal by the EBSD technique and the vickers hardness is shown in fig. 2:
as can be seen from fig. 2: at a Vickers hardness head of 136, the pressure perpendicular to the side surface of the pyramid when a load P is applied thereto is PnI.e. PnPsi (136 °/2). The surface area of the pyramid pressed into the metal is then: a ═ d ^2/(2sin (136 °/2)), i.e. the pressure caused by the indenter is σHV＝Pnand/A. The calculation formula of Vickers hardness is: HV 2Psin (136 °/2)/d ^ 2. In conclusion, the derivation formula of the relationship between Vickers hardness and stress can be obtained: sigmaHV＝0.9272HV。
The critical shear stress, also known as Schmid's law, refers to the minimum shear stress required for the initiation of a slip system or twin crystal, referred to as the critical shear stress. The calculation formula is τ ═ σ ═ m. Finally, the calculated stress σ is combined with the calculated Schmid factor valueHVAnd substituting a critical parting stress calculation formula to obtain the critical parting stress of the twin crystal.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings that are required to be used in the present application will be briefly described below.
FIG. 1 is a schematic view of a Vickers hardness indenter.
FIG. 2 is a schematic view of a Vickers hardness indentation geometry.
FIG. 3 is a metallographic image of the Zr-4 alloy before and after Vickers hardness compression.
FIG. 4 is an EBSD measurement analysis chart after Vickers hardness compression of Zr-4 alloy.
FIG. 5 is a schematic representation of the EBSD sample coordinate system.
Detailed Description
In order to make the objects, 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. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer.
Example 1
The method for calculating the critical slicing stress of the twin crystal by the EBSD technology and the Vickers hardness tester comprises the following steps:
1) preparation of EBSD samples (ensuring flatness of samples):
firstly, inlaying a sample on an inlaying machine, then using 150#, 320#, 800# and 2000# water sand paper to pre-grind in sequence, removing deeper scratches, and then carrying out vibration polishing on an automatic polishing machine, wherein the polishing solution is SiO2Polishing the nano suspension for about 1 hour to finally obtain a bright and traceless polished surface with a mirror surface effect;
2) marking a certain position on the surface of the sample by using Vickers hardness, and recording the original appearance and crystal orientation of the area by using a metallographic microscope, a scanning electron microscope and an EBSD (electron back scattering detector);
3) carrying out hardness measurement on the region through a Vickers hardness tester, replacing loads (from 10g to 1000g) with different sizes until twins appear beside the indentation, and recording the diagonal size and hardness value of the indentation;
4) determining the orientation of the crystal where the indentation is located through EBSD, obtaining a component force direction leading to twin crystal formation according to the geometric relation of the indentation, and calculating the value of Schmid factor of the twin crystal under the component force by combining the crystal structure calibrated by the EBSD;
5) finally, the stress size causing the twin crystal formation is obtained according to the geometric relation of the indentation, and the critical cutting stress of the twin crystal is finally obtained by combining the calculation result of the Schmid factor.
The following example 2 is specifically developed based on the method of calculating the critical slicing stress of the twin crystal by the EBSD technique and the vickers hardness tester in example 1, and is described here.
Example 2
The critical cutting stress of the {11-21} twin crystal is measured on the Zr-4 alloy in the beta phase zone quenching state by the method described above through the method for calculating the critical cutting stress of the twin crystal by the EBSD technology and the Vickers hardness tester.
The Zr-4 alloy has the nominal composition of Zr-1.5Sn-0.2Fe-0.1Cr, has very low thermal neutron absorption cross section, high hardness, ductility and excellent corrosion resistance, and is mainly used as a fuel cladding material in a pressurized water reactor, a boiling water reactor and a heavy water reactor.
Firstly, preparing an EBSD sample, namely preparing the EBSD sample by the processes of wire cutting, grinding, mechanical vibration polishing and the like. The morphology change before and after the vickers hardness indenter was pressed in was observed by a metallographic microscope, as shown in fig. 3. The test piece was held under a load of 500g for 10 seconds, and the hardness measured by a Vickers hardness tester was 162HV, and the average diagonal length was 102 μm. Calculating stress sigma according to indentation geometryHV873 MPa. Then, the orientation of the crystal grain with the Vickers hardness and the type of the twin- {11-21} twin were measured under a scanning electron microscope with an EBSD probe, and the results are shown in FIG. 4. As can be seen from FIG. 4, the formation of {11-21} twin crystals perpendicular to the sides of the indentation, combined with the EBSD sample coordinate system (shown in FIG. 5), imparts a force component PnCarried into the crystal structure (fig. 4), the Schmid factor value was calculated to be 0.37. Finally, the formula tau is equal to sigmaHVM, the critical cutting stress of the obtained {11-21} twin crystal is 323 MPa.
The invention is not the best known technology.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (5)
1. The method for calculating the critical cutting stress of the twin crystal by the EBSD technology and the Vickers hardness tester is characterized in that: firstly, forming twin crystals by using a Vickers hardness tester, and recording the diagonal length and the Vickers hardness value of the indentation at the moment; determining the orientation of the crystal where the indentation is located by an EBSD technology, obtaining a component force direction causing twin crystal formation according to the geometric relation of the indentation, and calculating the value of the Schmid factor of the twin crystal under the component force by combining the crystal structure calibrated by the EBSD; finally, combining with the value of Schmid factor, obtaining the critical cutting stress of twin crystal.
2. The method for calculating the critical slicing stress of twin crystals by the EBSD technique and the vickers hardness tester as set forth in claim 1, wherein: preparing an EBSD sample, determining a certain area of the sample in a metallographic microscope and the EBSD, and marking the position by using Vickers hardness; and then, carrying out hardness test on the region through Vickers hardness of different loads until twins appear beside the hardness indentation under a certain load, and recording the diagonal size and hardness value of the hardness indentation.
3. The method for calculating the critical slicing stress of the twin crystal through the EBSD technology and the Vickers hardness tester according to the claim 2 is characterized by comprising the following specific steps:
1) preparing an EBSD (Electron Back scattering) block sample, and ensuring the flatness of the surface of the sample through chemical wiping corrosion or mechanical vibration polishing;
2) marking a certain position on the surface of the sample by using Vickers hardness, and recording the original appearance and crystal orientation of the area by using a metallographic microscope, a scanning electron microscope and an EBSD (electron back scattering detector);
3) carrying out hardness measurement on the region through a Vickers hardness tester, replacing loads with different sizes until twin crystals appear beside the indentation under a certain load, and recording the diagonal size and hardness value of the indentation;
4) determining the orientation of the crystal where the indentation is located through EBSD, obtaining a component force direction leading to twin crystal formation according to the geometric relation of the indentation, and calculating the value of Schmid factor of the twin crystal under the component force by combining the crystal structure calibrated by the EBSD;
5) and obtaining the stress size causing the twin crystal formation according to the geometrical relation of the indentation, and finally obtaining the critical cutting stress of the twin crystal by combining the calculation result of the Schmid factor.
4. The method for calculating the critical slicing stress of twin crystals by the EBSD technique and the vickers hardness tester as set forth in claim 1, wherein in the step 1), the surface of the sample is treated by any one of the following methods:
the method comprises the following steps:
pre-grinding and polishing: pre-grinding with 150#, 320#, 800# and 2000# water sand paper, removing deep scratches, and mechanically polishing with SiO as polishing solution2Polishing the nano turbid liquid for 6-10 minutes to finally obtain a bright and traceless polished surface with a mirror surface effect;
etching: gently and rapidly wiping the surface of the sample for 3-10 seconds by using cotton stained with acid until the surface of the sample becomes bright, washing the sample by using clean water and absolute ethyl alcohol in sequence, and finally drying and storing;
the second method comprises the following steps:
firstly, inlaying a sample on an inlaying machine, then using 150#, 320#, 800# and 2000# water sand paper to pre-grind in sequence, removing deeper scratches, and finally performing vibration polishing on an automatic polishing machine, wherein the polishing solution is SiO2Polishing the nano suspension for 0.5-1 hour to obtain a bright and traceless polished surface with a mirror surface effect.
5. The method for calculating the critical slicing stress of twin crystals by the EBSD technique and the vickers hardness tester as set forth in claim 1, wherein: and 3) replacing loads with different sizes from 10g to 1000g until twins appear beside the indentation under a certain load.
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