Multi-principal element alloy local lattice distortion measurement method based on synchrotron radiation X-ray atom pair distribution function

Abstract

The invention relates to a multi-principal element alloy local lattice distortion measurement method based on a synchrotron radiation X-ray atom pair distribution function, which comprises the following steps: preparing an experimental material, and collecting two-dimensional diffraction data by using synchrotron radiation high-energy X-rays; separating local and average structure information through an atom pair distribution function; and verifying local distortion causes by combining structure fitting and DFT supercell relaxation. According to the method, the accuracy of capturing the local distortion of the atomic scale can be improved, the integrity of statistical information of the local structure distortion of the quantitative characterization material can be fully supplemented, and high-precision measurement and quantitative analysis of dynamic distortion can be systematically realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of material characterization, and particularly relates to a precise measurement method for the local structure of multi-principal element alloys, and more particularly to a quantitative characterization technique for local lattice distortion combining synchrotron radiation X-ray powder diffraction, atomic pair distribution function analysis, and density functional theory verification. Background Art

[0002] The analysis of the local structure of traditional alloys mostly relies on transmission electron microscopy (TEM) or conventional X-ray diffraction, and has the following limitations:

[0003] 1. Resolution limitation: Since the local structure distortion destroys the local crystal structure, it causes diffuse scattering in diffraction measurements, and it is difficult to capture the local distortion at the atomic scale based on the analysis of diffraction peaks by conventional X-ray diffraction;

[0004] 2. Insufficient data integrity: TEM can only provide local microscopic image information with limited accuracy, and cannot quantitatively characterize the statistical information of the local structure distortion of materials;

[0005] 3. Dependence on static models: Existing methods mostly rely on the ideal lattice hypothesis, ignoring dynamic distortion and chemical short-range order effects.

[0006] In recent years, the influence of the complex local environment of multi-principal element alloys on properties such as mechanics, radiation resistance, and catalysis has attracted much attention, but there is no systematic method that can simultaneously achieve high-precision measurement and quantitative analysis of dynamic distortion. Summary of the Invention

[0007] The problem solved by the present invention is to provide a method for measuring the local lattice distortion of multi-principal element alloys based on synchrotron radiation X-ray atomic pair distribution function, which solves the problems raised in the above background art.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for measuring the local lattice distortion of multi-principal element alloys based on synchrotron radiation X-ray atomic pair distribution function, characterized by comprising the following steps:

[0010] Step 1. Sample preparation, homogenize the alloy, grind and crush it to eliminate the influence of texture;

[0011] Step 2. Experimental design, use synchrotron radiation high-energy X-rays to collect two-dimensional diffraction data; perform two-dimensional powder diffraction using synchrotron radiation high-energy X-rays (energy ≥ 60 keV), covering the Q value range and convert the diffraction data into an atomic pair distribution function through Fourier transform;

[0012] Step 3. Parameter extraction: By fitting and analyzing the pair distribution function of atoms, local and average structural information is separated; the isotropic atomic displacement parameter (Uiso) is obtained by performing structural fitting analysis on the powder diffraction signal, and the sum of dynamic and static distortions is quantified.

[0013] Step 4. Calculation and verification: Combining the density functional theory (DFT) relaxed supercell and structural fitting to verify the origin of local distortion; constructing a quasi-random supercell model based on DFT, and simulating the local atomic displacement through ion relaxation; using the DFT relaxation model to fit and match the experimental pair distribution function of atoms to verify the physical origin of local distortion.

[0014] The beneficial effects of the present invention are as follows:

[0015] 1. It can improve the accuracy of capturing local distortion at the atomic scale.

[0016] 2. It can fully supplement the integrity of the statistical information for quantitatively characterizing the local structural distortion of materials.

[0017] 3. It can systematically achieve high-precision measurement and quantitative analysis of dynamic distortion.

[0018] As an improved technical solution, the particle size of the alloy particles in the experiment is <50 μm.

[0019] As an improved technical solution, the calculation of the local strain ε 1st needs to satisfy a goodness of fit R < 10%.

[0020] As an improved technical solution, the local strain (ε 1st ) is calculated by the first peak position shift, and the formula is: ε 1st = (a 1st – a ave ) / a ave , where a 1st is the lattice constant fitted by the first nearest neighbor atomic spacing, and a ave is the lattice constant of the average structure. Description of the drawings

[0021] Figure 1 is NiCoPd ground by a mechanical grinder to a particle size <50 μm.

[0022] Figure 2 is the radial distribution function of NiCoPd.

[0023] Figure 3 is the GSAS fitting analysis of the powder diffraction pattern.

[0024] Figure 4 is the full-spectrum fitting analysis of the radial distribution function of NiCoPd.

[0025] Figure 5 It is the supercell structure model after DFT relaxation.

[0026] Figure 6 It is based on the full-spectrum fitting of the DFT supercell structure.

[0027] Figure 7 It is the distribution of the first-nearest neighbor atomic pairs based on the DFT supercell. Specific implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0029] A method for measuring local lattice distortion of a multi-principal element alloy based on synchrotron radiation X-ray atomic pair distribution function, which is characterized by including the following steps:

[0030] Step 1. Sample preparation: homogenize the alloy, grind and crush it. The particle size of the alloy particles for the test is <50 μm to eliminate the influence of texture.

[0031] Step 2. Experimental design: use synchrotron radiation high-energy X-rays to collect two-dimensional diffraction data; perform two-dimensional powder diffraction using synchrotron radiation high-energy X-rays (energy ≥ 60 keV), covering the Q value range and convert the diffraction data into an atomic pair distribution function through Fourier transform; calculate the local strain (ε 1st ) through the first peak position shift of the atomic pair distribution function. The formula is: ε 1st =(a 1st –a ave ) / a ave , where a 1st is the lattice constant fitted by the first-nearest neighbor atomic spacing, and a ave is the lattice constant of the average structure. The calculation of the local strain ε 1st needs to satisfy a goodness of fit R < 10%.

[0032] Step 3. Parameter extraction: separate the local and average structure information through fitting analysis of the atomic pair distribution function; use the structure fitting analysis of the powder diffraction signal to obtain the isotropic atomic displacement parameter (U i so) to quantify the total sum of dynamic and static distortions.

[0033] Step 4. Computational verification: combine density functional theory (DFT) relaxation supercell with structural fitting to verify the cause of local distortion; construct a quasi-random supercell model based on DFT, and simulate local atomic displacement through ion relaxation; use the DFT relaxation model to fit and match the experimental atomic pair distribution function to verify the physical source of local distortion.

[0034] The beneficial effects of the present invention are that it can improve the accuracy of capturing local distortion at the atomic scale, can fully supplement the integrity of statistical information for quantitatively characterizing local structural distortion of materials, and can systematically achieve high-precision measurement and quantitative analysis of dynamic distortion. The above data can be statistically included in the atomic pair distribution function fitting module and the DFT verification database, providing data support for further research and development.

[0035] Taking the local structure analysis of NiCoPd multi-principal alloy as an example, the specific steps are as follows:

[0036] 1. Sample preparation: Prepare homogenized NiCoPd alloy by arc melting and grind it mechanically to a particle size of <50 μm using a diamond grinder;

[0037] 2. Data collection: Two-dimensional diffraction experiments were performed at a synchrotron radiation facility, wavelength Detector distance>160mm; reference Figure 1 As shown, Figure 1 This is the two-dimensional diffraction pattern of NiCoPd. The diffraction ring intensity is uniform and there is no texture and other impurity phase signals.

[0038] 3. Atomic pair distribution function analysis: Use PDFgetX3 software to perform Fourier transform on the diffraction data to obtain the radial distribution function G(r); refer to Figure 2 As shown, Figure 2 The data points in the middle circle are the atomic pair distribution functions of NiCoPd.

[0039] 4. Fitting and verification: GSAS software was used to fit the powder diffraction pattern to obtain the isotropic atomic displacement parameter U iso; Figure 3 As shown, the cross represents the experimental data point, the upper dotted line represents the fitting curve, and the lower solid line represents the difference curve between the two. PDFGUI software was used to perform short-range fitting on G(r) like Figure 2 As shown, the red solid line is the short-range fitting curve based on the face-centered cubic crystal structure, and the green solid line is the difference curve between the two. PDFGUI software was used to fit the full spectrum of G(r). Get the average structure lattice constant a ave .like Figure 4As shown, the solid line above is the short-range fitting curve based on the face-centered cubic crystal structure, and the solid line below is the difference curve between the two.

[0040] The calculation formula is:

[0041] ε 1st =(a 1st –a ave ) / a ave =(3.7015 - 3.6813) / 3.6813 = 0.68%;

[0042] Referring to Figures 5 - 7 as shown, the relaxed DFT supercell model is used to obtain the low-energy supercell structure; the total spectrum fitting of the pair distribution function of atoms is carried out using this structure; the statistical analysis of the nearest-neighbor pair distribution of the DFT supercell shows that there is local expansion around the Pd atoms, which is consistent with the right shift of the first peak of the pair distribution function of atoms.

[0043] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A method for measuring local lattice distortion of multi-principal alloys based on synchrotron radiation X-ray atomic pair distribution function, characterized in that: The following steps are involved: Step 1. Sample preparation, homogenization of alloy, grinding and crushing to eliminate texture effects; Step 2. Experimental design, using synchrotron radiation high-energy X-rays to collect two-dimensional diffraction data; Two-dimensional powder diffraction using synchrotron radiation high-energy X-rays (energy ≥ 60keV) covering the Q value range And the diffraction data are converted into atomic pair distribution functions by Fourier transformation; Step 3. Parameter extraction: separate the local and average structural information through atomic pair distribution function fitting analysis; obtain the isotropic atomic displacement parameter (Uiso) by structural fitting analysis of powder diffraction signals to quantify the sum of dynamic and static distortions; Step 4. Computational verification: combine density functional theory (DFT) relaxation supercell with structural fitting to verify the cause of local distortion; construct a quasi-random supercell model based on DFT, and simulate local atomic displacement through ion relaxation; use the DFT relaxation model to fit and match the experimental atomic pair distribution function to verify the physical source of local distortion.

2. The method for measuring local lattice distortion of multi-principal alloys based on synchrotron radiation X-ray atom pair distribution function according to claim 1, characterized in that The particle size of the tested alloy particles was <50 μm.

3. The method for measuring local lattice distortion of multi-principal alloys based on synchrotron radiation X-ray atom pair distribution function according to claim 1, characterized in that The local strain ε 1st The calculation must satisfy the goodness of fit R < 10%.

4. The method for measuring local lattice distortion of multi-principal alloys based on synchrotron radiation X-ray atom pair distribution function according to claim 1, characterized in that The local strain (ε 1st ), the formula is: 1st =(a 1st –a ave ) / a ave , where a 1st is the first nearest neighbor atomic spacing fitting lattice constant, a ave is the average structure lattice constant.

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