A method for nondestructively monitoring grain boundary relaxation strengthening of nanometals and a method for determining process parameters

Abstract

The present invention discloses a method for non-destructively monitoring grain boundary relaxation strengthening of nanometals and a method for determining process parameters. The monitoring method comprises the following steps: (1) using an X-ray diffractometer to obtain diffraction patterns of at least two diffraction crystal planes during the nanometal grain boundary relaxation process; (2) calculating the interplanar spacing of each diffraction crystal plane during the nanometal grain boundary relaxation process; and (3) calculating the lattice strain of each diffraction crystal plane during the nanometal grain boundary relaxation process. The present invention proposes for the first time the use of X-ray diffraction technology to in-situ monitor the change in interplanar spacing during grain boundary relaxation (low-temperature heat treatment), using average lattice strain as a microstructural characteristic indicator that accurately reflects the degree of grain boundary relaxation. This effectively solves the problems of difficulty in determining heat treatment process parameters and ensuring the grain boundary relaxation strengthening effect, and provides process guidance and quality assurance for the preparation of high-performance nanometal materials using high-efficiency, low-energy heat treatment designs.

Description

Technical Field

[0001] The present invention relates to the technical field of material mechanics, and in particular to a method for non-destructively monitoring grain boundary relaxation strengthening of nano-metals and a method for determining process parameters. Background Art

[0002] Nanometals generally have better mechanical, wear and corrosion resistance than traditional polycrystalline materials, and have broad application prospects in many fields such as petrochemicals, aerospace, and medical devices. At present, nanometal materials are mainly prepared by deposition or severe plastic deformation. Such materials contain a large number of thermodynamically non-equilibrium grain boundaries and have poor thermal stability. During heat treatment at low temperatures (below the grain coarsening temperature), the grain boundary structure will be stabilized and a large amount of excess free energy will be released. Different from the traditional understanding that annealing induces material softening, the grain boundary relaxation induced by low-temperature annealing can further improve the mechanical properties of nanometal materials.

[0003] Compared to traditional material strengthening methods, grain boundary relaxation (GBR) can be achieved through efficient, low-energy, and simple low-temperature heat treatment, offering a novel approach to regulating the microstructure and properties of nanometals. In recent years, numerous researchers, both domestically and internationally, have conducted exploratory research on the GBR-strengthening effect in nanometals. Scanning electron microscopy observations and analyses have confirmed the ordering of the grain boundary structure during relaxation; differential scanning calorimetry has determined that approximately 7% of excess energy is released during GBR; and microhardness evaluations and analyses have confirmed that the rapid diffusion and annihilation of excess vacancies control the GBR dynamics. Relaxation strengthening is closely related to annealing temperature and time, demonstrating a typical thermally activated process. However, these techniques fail to establish accurate nanostructure-mechanical property correlations, hindering the practical engineering application of GBR-strengthening nanometals. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for non-destructive monitoring of grain boundary relaxation strengthened nanometals and a method for determining process parameters, aiming to solve the technical problem that the existing technology cannot construct an accurate nanostructure-mechanical property correlation and is difficult to realize the practical engineering application of grain boundary relaxation strengthened nanometals.

[0005] To achieve the above object, the present invention provides a method for non-destructively monitoring grain boundary relaxation strengthening of nanometals, comprising the following steps:

[0006] (1) using an X-ray diffractometer to obtain a diffraction pattern of at least one diffraction crystal plane during the relaxation process of the nanometal grain boundary;

[0007] (2) using the centroid method to determine the position of the diffraction peak of each diffraction crystal plane, and then calculating the interplanar spacing of each diffraction crystal plane during the nanometal grain boundary relaxation process according to the position of the diffraction peak of each diffraction crystal plane;

[0008] (3) The lattice strain of each diffraction crystal plane during the relaxation of the nanometal grain boundary is calculated based on the interplanar spacing of each diffraction crystal plane during the relaxation of the nanometal grain boundary.

[0009] Furthermore, in step (1), the X-ray diffractometer uses a 2θ-θ scanning mode, a continuous scanning rate is less than 2° / min, and a scanning step size is less than 0.05°.

[0010] Furthermore, in step (2), the calculation formula of the interplanar spacing is shown in the following formula 1:

[0011]

[0012] Among them, d (hkl) represents the interplanar spacing, n represents the diffraction order, λ represents the X-ray wavelength, and θ represents the Bragg angle.

[0013] Furthermore, in step (3), the calculation formula of the lattice strain is shown in the following formula 2:

[0014]

[0015] Among them, e (hkl) represents the lattice strain, d′ (hkl) represents the interplanar spacing of the diffraction planes during grain boundary relaxation, Represents the initial interplanar spacing of the diffraction crystal planes.

[0016] Furthermore, in step (1), the diffraction patterns of at least two diffraction crystal planes during the nanometal grain boundary relaxation process are obtained, and the method further includes the following steps arranged after step (3):

[0017] (4) Calculate the average value of the lattice strain of each diffraction crystal plane during the relaxation process of nanometal grain boundaries.

[0018] Furthermore, in step (4), the calculation formula for obtaining the average value is shown in the following formula 3:

[0019]

[0020] in, represents the average lattice strain, represents the lattice strain of the mth diffraction crystal plane, and m represents the number of diffraction crystal planes.

[0021] The present invention also provides a method for determining process parameters for grain boundary relaxation strengthening of nanometals, which involves a low-temperature heat treatment process for inducing grain boundary relaxation of nanometals, comprising the following steps:

[0022] (1) obtaining the lattice strain of a single diffraction crystal plane or the average value of the lattice strains of at least two diffraction crystal planes during the nanometal grain boundary relaxation process using the above-described method;

[0023] (2) Find the peak value of the lattice strain of a single diffraction crystal plane or the average value of the lattice strain of at least two diffraction crystal planes during the nanometal grain boundary relaxation process. The time when the peak value appears is the optimal processing time.

[0024] X-ray diffraction is often used to statistically analyze the microstructural characteristics of crystalline materials, such as grain size, microstrain, and lattice parameters. Related research results show that grain boundary relaxation does not change the grain size of nanometals, but increases the intensity of the diffraction peak and reduces the half-height width or integrated width of the diffraction peak, confirming that the nanostructure undergoes an ordered transformation and the microstrain is reduced. Since abnormal grain growth occurs immediately after grain boundary relaxation, it also improves the integrity of the crystal structure. Therefore, the diffraction peak intensity and width cannot accurately reflect the degree of relaxation of non-equilibrium grain boundaries during the annealing process. Therefore, exploring and discovering effective microstructural characteristic indicators is a key technical problem in realizing the engineering application of nanometals strengthened by grain boundary relaxation.

[0025] For metastable nanometal materials containing a large number of non-equilibrium grain boundaries, grain boundary relaxation occurs during low-temperature heat treatment and improves the mechanical properties of the material. Non-destructive X-ray diffraction technology is used to in-situ monitor the changes in the interplanar spacing during the nanometal grain boundary relaxation process. Based on the diffusion and annihilation of excess vacancies involved in non-equilibrium grain boundary relaxation, lattice strain is induced. When the average lattice strain reaches a peak value, that is, the non-equilibrium grain boundaries are completely relaxed, the optimal heat treatment process parameters are determined, and high-strength nanometal materials are obtained. Nanometal materials prepared by deposition or deformation contain a large number of thermodynamically non-equilibrium grain boundaries. Grain boundary relaxation occurs during low-temperature heat treatment, improving the mechanical properties of the material. The average lattice strain accurately reflects the degree of relaxation of the non-equilibrium grain boundaries. The maximum average lattice strain corresponds to the completely relaxed state of the grain boundaries. The optimal heat treatment process parameters are determined based on the average lattice strain peak value, and the optimal grain boundary relaxation strengthening effect is obtained. Based on the evolution behavior of the average lattice strain and combined with high-efficiency and low-energy heat treatment, high-performance nanometal materials can be flexibly designed and prepared.

[0026] This method enables non-destructive monitoring of the strengthening effect of grain boundary relaxation on nanometals. The basic principle of this method is that the relaxation process of non-equilibrium grain boundaries in metastable nanometals primarily involves the diffusion and annihilation of excess vacancies. The activity of excess vacancies causes gradual changes in the interplanar spacing, resulting in lattice strain. When the average lattice strain reaches its peak, the non-equilibrium grain boundaries are completely relaxed. Using X-ray diffraction technology to non-destructively analyze the interplanar spacing and average lattice strain in situ, the degree of grain boundary relaxation can be accurately monitored, thereby determining optimal heat treatment process parameters and achieving high-strength nanometal materials.

[0027] The method of the present invention for non-destructive monitoring of grain boundary relaxation strengthening of nanometals proposes for the first time the use of X-ray diffraction technology to in situ monitor the changes in interplanar spacing during grain boundary relaxation (low-temperature heat treatment), using average lattice strain as a microstructural characteristic indicator that accurately reflects the degree of grain boundary relaxation. This effectively solves the problems of difficulty in determining heat treatment process parameters and difficulty in ensuring the grain boundary relaxation strengthening effect, and provides process guidance and quality assurance for the preparation of high-performance nanometal materials using high-efficiency and low-energy heat treatment design.

[0028] The proposed method for nondestructively monitoring grain boundary relaxation strengthening of nanometals uses X-ray diffraction to nondestructively analyze the changes in interplanar spacing and average lattice strain induced by excess vacancy activity during grain boundary relaxation. This accurately reflects the extent of nonequilibrium grain boundary relaxation and its strengthening effect, thereby determining optimal heat treatment process parameters and producing high-strength nanometal materials. This provides strong technical support for the design and preparation of high-performance nanometal materials using efficient, low-energy heat treatments.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) The present invention is an efficient, simple and reliable non-destructive testing method.

[0031] (2) The change in average lattice strain induced by excess vacancy activity accurately reflects the degree of grain boundary relaxation and strengthening effect, which can be used to determine the optimal heat treatment process parameters and provide reliable process guidance and quality assurance for the actual engineering application of grain boundary relaxation strengthened nanometal materials.

[0032] (3) Based on the reliable average lattice strain-mechanical property correlation, high-strength nanometal materials can be flexibly designed and prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the grain boundary relaxation strengthening nanometal monitoring process of the present invention;

[0034] Figures 2 to 4 Low temperature annealing grain boundary relaxation strengthening nanometals and related microstructural evolution, among which, Figure 2 The microhardness of the nano-Ni obtained in the embodiment is improved during the grain boundary relaxation process; Figure 3 The evolution of (111) interplanar spacing during the grain boundary relaxation process of nano-Ni obtained in Example; Figure 4 The evolution of the interplanar spacing of (200) nano-Ni during the grain boundary relaxation process obtained in Example;

[0035] Figure 5 The figure shows the evolution of the average lattice strain of the nano-Ni during the grain boundary relaxation process obtained in the embodiment.

[0036] Explanation of the marks in the figure: 1—heat treatment device; 2—nanometallic material; 3—incident X-ray; 4—reflected X-ray; 5—material surface normal; 6—initial state diffraction peak; 7—relaxation state diffraction peak; 8—diffraction peak position; 9—relaxation-induced diffraction peak shift. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0038] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0039] The nondestructive monitoring of grain boundary relaxation strengthening of the present invention is achieved by Figure 1 The illustrated facility implements a low-temperature heat treatment device 1 on a nanometal material 2. The material is then scanned using an X-ray diffractometer. Initial-state diffraction peaks 6 and relaxation-state diffraction peaks 7 are collected in situ using a diffraction geometry formed by incident X-rays 3, reflected X-rays 4, and the material surface normal 5. The interplanar spacing and average lattice strain are calculated based on the diffraction peak positions 8 and relaxation-induced diffraction peak shifts 9, respectively. Based on the change in average lattice strain, optimal heat treatment process parameters can be determined, resulting in a high-strength nanometal material.

[0040] The following provides an example of a method for non-destructive monitoring of low temperature annealing grain boundary relaxation strengthened nano-Ni.

[0041] Example 1

[0042] In this embodiment, pure Ni prepared by electrodeposition is used as metastable nanomaterial with an average grain size of 28 nm. Low temperature annealing treatment is performed at 220°C, 250°C and 280°C respectively. Figure 1 The nondestructive monitoring method of grain boundary relaxation strengthening shown in the figure determines the optimal heat treatment process parameters by collecting diffraction peaks, analyzing crystal plane spacing and average lattice strain, and obtaining high-strength nano-Ni.

[0043] Specific steps combined Figure 1 The schematic diagram of the nondestructive monitoring process is shown in Figures 2 to 5 The monitoring and analysis results of the embodiment shown are described in detail:

[0044] (1) Using the electrodeposition method, a disk-shaped (radius of 1.5 cm, thickness of 65 μm) nano-pure Ni was prepared in a plating solution composed of nickel sulfate, nickel chloride, boric acid, sodium eicosyl sulfate and saccharin. The deposited nano-Ni contained a large number of non-equilibrium grain boundaries. The nano-Ni was placed in a heat treatment device and heated to 220℃, 250℃ and 280℃ at a rate of 10℃ / min for isothermal treatment. During the heat treatment, the non-equilibrium grain boundaries relaxed, and the microhardness of the material increased with the increase in the degree of relaxation. The higher the isothermal temperature, the faster the hardness increase rate, that is, the nano-Ni underwent grain boundary relaxation strengthening. For example, after isothermal treatment at 220℃ for 4600s, the hardness increased from 4.75GPa to 5.18GPa, and after isothermal treatment at 280℃ for 1200s, the hardness increased from 5.12GPa to 5.43GPa. After the grain boundaries are completely relaxed, the nano-scale grains immediately grow abnormally. Prolonging the isothermal time will lead to a decrease in the hardness of the material, that is, abnormal grain growth induces softening, and the softening rate of the material is positively correlated with the isothermal temperature. Figure 2 .

[0045] (2) For metal Ni with a face-centered cubic structure, the X-ray diffraction method can be used to obtain the diffraction peaks of crystal planes (111), (200), (220), (311), and (222) (diffraction angles from low to high) in sequence; in order to ensure the quality of the diffraction peaks, a diffractometer equipped with a Co target was used to obtain in situ the diffraction patterns of Ni (111) and (200) during grain boundary relaxation within the scanning ranges of 49°–54° and 58°–63°, respectively. The 2θ-θ scanning mode was selected, the continuous scanning rate was 1° / min, the scanning step was 0.005°, and the acquisition time of a single diffraction peak was 5 min.

[0046] (3) The position (2θ) of the collected diffraction peak is determined by the centroid method, that is, the 2θ value corresponding to the centroid of the diffraction peak geometry is solved, and the interplanar spacing between (111) and (200) is further calculated using the following formula 1:

[0047]

[0048] Among them, d (hkl) – (hkl) interplanar spacing, n – diffraction order (for (111) plane d (111) , n=1; for (200) crystal plane d (200) , n = 2), λ – X-ray wavelength (when using Co target, the wavelength is 0.178897 nm), θ – Bragg angle.

[0049] The relaxation of non-equilibrium grain boundaries in nano-Ni does not change the grain size and is mainly characterized by the ordering of the grain boundary structure. The kinetic process is dominated by the rapid diffusion and annihilation of excess vacancies.

[0050] During the grain boundary relaxation process, the interplanar spacing of nano-Ni (111) and (200) increases with the extension of the isothermal time, and the rate of increase is positively correlated with the isothermal temperature. For example, after isothermal treatment at 220℃ for 4600s, the interplanar spacing of (111) and (200) increases from 0.20642nm and 0.17835nm to 0.20654nm and 0.17841nm, respectively. After isothermal treatment at 280℃ for 1200s, the interplanar spacing of (111) and (200) increases rapidly to 0.20664nm and 0.17851nm, respectively. Figure 3 and Figure 4 By Figure 2 By comparison, it can be seen that in the grain boundary relaxation strengthening zone, the interplanar spacing and microhardness have similar evolution behaviors; in the softening zone induced by abnormal grain growth, the Ni (111) and (200) interplanar spacings do not change.

[0051] (4) The (111) and (200) lattice strains during grain boundary relaxation are calculated using the following formula 2:

[0052]

[0053] Among them, e (hkl) –(111) or (200) lattice strain, d′ (hkl) – (111) or (200) interplanar spacing during grain boundary relaxation, – Initial (111) or (200) interplanar spacing.

[0054] (5) The average lattice strain of nano-Ni is further calculated using the following formula 3:

[0055]

[0056] in, – Average lattice strain. The average lattice strain of nano-Ni varies with isothermal time and isothermal temperature. Figure 5 It can be seen that after isothermal treatment at 220℃, 250℃ and 280℃, the peak values ​​of the average lattice strain of nano-Ni are 0.053%, 0.080% and 0.102% respectively.

[0057] The average lattice strain can accurately reflect the relaxation degree of the non-equilibrium grain boundary of nano-Ni. The maximum average lattice strain corresponds to the complete relaxation state of the grain boundary. Figure 2 and Figure 5 .

[0058] According to the average lattice strain peak, the optimal heat treatment process parameters of nano-Ni can be determined as 220℃+1200s, 250℃+2200s and 280℃+4600s, which correspond to microhardness increases of 9.1%, 12.3% and 14.3%, respectively.

[0059] Based on the evolution behavior of the average lattice strain of nano-Ni during grain boundary relaxation, combined with high-efficiency and low-energy heat treatment below 280°C, nano-Ni materials with hardness between 4.75GPa and 5.43GPa can be flexibly designed and prepared.

[0060] In the present invention, in addition to using the average lattice strain of the material to monitor grain boundary relaxation strengthening, special attention should be paid when using a low-temperature heat treatment process to achieve the purpose of grain boundary relaxation strengthening: the metastable nanometal material can be treated by heating or isothermal treatment, but the maximum temperature must be lower than the nanoscale grain coarsening temperature, and for isothermal treatment, the isothermal time must be strictly controlled, otherwise abnormal grain growth will occur, resulting in material softening.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for non-destructive monitoring of grain boundary relaxation strengthening of nanometals, characterized in that: The following steps are involved: (1) Using an X-ray diffractometer, obtaining a diffraction pattern of at least one diffraction crystal plane during the relaxation process of the nanometal grain boundary; (2) The center of gravity method is used to determine the position of the diffraction peak of each diffraction crystal plane, and then the interplanar spacing of each diffraction crystal plane during the nanometal grain boundary relaxation process is calculated based on the position of the diffraction peak of each diffraction crystal plane; the calculation formula of the interplanar spacing is shown in the following formula 1: Formula 1 in, d (hkl) represents the interplanar spacing, n represents the diffraction order, λ represents the wavelength of X-rays, θ represents the Bragg angle; (3) The lattice strain of each diffraction crystal plane during the nanometal grain boundary relaxation process is calculated based on the interplanar spacing of each diffraction crystal plane during the nanometal grain boundary relaxation process. The calculation formula of the lattice strain is shown in the following formula 2: Formula 2 in, e (hkl) represents the lattice strain, represents the interplanar spacing of the diffraction planes during grain boundary relaxation, Represents the initial interplanar spacing of the diffraction crystal planes.

2. The method for nondestructive monitoring of grain boundary relaxation strengthening of nanometal according to claim 1, wherein: In step (1), the X-ray diffractometer is 2 θ-θ In scanning mode, the continuous scanning rate is less than 2° / min and the scanning step size is less than 0.05°.

3. The method for nondestructive monitoring of grain boundary relaxation strengthening of nanometal according to claim 1, wherein: In step (1), the diffraction patterns of at least two diffraction crystal planes during the nanometal grain boundary relaxation process are obtained, and the method further includes the following steps arranged after step (3): (4) Calculate the average value of the lattice strain of each diffraction crystal plane during the relaxation process of nanometal grain boundaries.

4. The method for nondestructive monitoring of grain boundary relaxation strengthening of nanometal according to claim 3, wherein: In step (4), the calculation formula for obtaining the average value is shown in the following formula 3: Formula 3 in, represents the average lattice strain, represents the lattice strain of the mth diffraction crystal plane, and m represents the number of diffraction crystal planes.

5. The method for nondestructive monitoring of grain boundary relaxation strengthening of nanometal according to any one of claims 1 to 4, characterized in that: The degree of relaxation of the non-equilibrium grain boundary is reflected by the lattice strain of a single diffraction crystal plane or the average value of the lattice strain of at least two diffraction crystal planes during the relaxation process of the nanometal grain boundary. The maximum value of the lattice strain of a single diffraction crystal plane or the average value of the lattice strain of at least two diffraction crystal planes during the relaxation process of the nanometal grain boundary corresponds to the state of complete relaxation of the grain boundary.

6. A method for determining process parameters for grain boundary relaxation strengthening of nanometals, involving a low-temperature heat treatment process to induce grain boundary relaxation of nanometals, characterized in that: The following steps are involved: (1) Obtaining the lattice strain of a single diffraction crystal plane or the average value of the lattice strains of at least two diffraction crystal planes during the nanometal grain boundary relaxation process by the method according to any one of claims 1 to 5; (2) Find the peak value of the lattice strain of a single diffraction crystal plane or the average value of the lattice strain of at least two diffraction crystal planes during the relaxation process of the nanometal grain boundary. The time when the peak value appears is the optimal processing time.

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