Method for judging tungsten recrystallization inhibition condition

Abstract

The invention belongs to the field of fusion engineering, and particularly discloses a method for judging tungsten recrystallization inhibition conditions. According to the method, a new correlation formula for suppressing tungsten recrystallization through helium plasma irradiation is provided, the tungsten recrystallization suppression condition is evaluated according to the relation between the value T and the value I, the situation that in traditional research, the tungsten recrystallization suppression condition is evaluated under the condition that Zener resistance does not dominate is explained, and the situation that the tungsten recrystallization suppression condition is evaluated under the condition that Zener resistance does not dominate is explained besides traditional helium bubble pinning grain boundary suppression recrystallization. A new mechanism for inhibiting recrystallization is found. According to the method, a new path can be provided for research on inhibition of tungsten recrystallization through helium plasma irradiation in the future, the recrystallization behavior of the fusion reactor tungsten material is predicted, damage caused by recrystallization of a divertor and a first wall in a fusion device can be better prevented, and the purpose of predicting the service life of the fusion device more accurately is achieved.

Description

Technical Field

[0001] This invention belongs to the field of fusion engineering, and specifically relates to a method for judging the inhibition of tungsten recrystallization. Background Technology

[0002] Energy is a crucial driving force for the development of human civilization. However, the main energy sources available to humanity are non-renewable, such as oil and natural gas. While these resources have propelled societal progress, they have also brought serious problems such as environmental pollution and climate change. In contrast, deuterium, the raw material for nuclear fusion, is abundant in seawater and virtually inexhaustible, while the radioactivity of the nuclear waste produced during the fusion process is extremely limited. Therefore, adopting fusion energy to replace non-renewable energy sources is one of the important ways to solve future energy problems.

[0003] In fusion devices, plasma-facing materials are mainly used in the first wall of the blanket and divertor components. Tungsten, with its high melting point, high strength, and low physical sputtering, is considered one of the candidate materials for the divertor and first wall of future fusion devices. Since it needs to be in direct contact with plasma in the fusion reactor, it will be subjected to three types of heat loads simultaneously: high heat load, neutron irradiation damage, and plasma exposure. The service environment is extremely harsh, with the steady-state heat load power density reaching 10-20 MW / m³ during steady-state operation. 2 The presence of helium plasma irradiation will bring the surface of the tungsten divertor to a high temperature of thousands of degrees, causing the tungsten material to undergo recovery, recrystallization and grain growth, resulting in a significant decrease in the physical properties of tungsten. The presence of helium plasma irradiation will inhibit the recrystallization process.

[0004] Based on the aforementioned issues, the study of tungsten recrystallization suppression under high thermal loads has been a focus of attention for many scholars in order to more accurately predict the service life of tungsten divertors. Currently, the main research results on tungsten recrystallization suppression behavior are Zener resistance generated by helium bubble pinning of grain boundaries on the subsurface after helium plasma irradiation. However, this research has important prerequisites: Zener resistance is the dominant term and the helium bubbles must be located on high-angle grain boundaries of the recrystallized grains. This still cannot explain the recrystallization suppression behavior dominated by grain boundary curvature resistance when Zener resistance is weaker. Therefore, there is an urgent need for an evaluation method for tungsten recrystallization suppression under helium plasma irradiation to overcome the problem of neglecting grain boundary curvature resistance in traditional methods and to evaluate the tungsten recrystallization suppression behavior. Summary of the Invention

[0005] To address the problem of neglecting grain boundary curvature resistance in assessing the suppression of tungsten recrystallization behavior in conventional methods, the present invention provides a method for judging the suppression of tungsten recrystallization.

[0006] To achieve the above objectives, the following technical solutions are specifically included: This invention provides a method for determining the inhibition of tungsten recrystallization, comprising the following steps: S1. The tungsten sample undergoes surface pretreatment, followed by EBSD (backscattered electron diffraction) analysis to obtain the KAM (kernel average misorientation) pattern. Based on the KAM pattern, the orientation gradient Ω, shape factor α, and critical orientation difference angle θ are determined. m And calculate and determine the range of the threshold T according to the following relationship 1; (1), In the formula, Ω represents the orientation gradient, with units of °um. -1 ; α is the shape factor; θ m The critical orientation difference angle, in degrees; S2. The tungsten sample is subjected to helium plasma irradiation to create helium bubbles in the tungsten sample, resulting in an irradiated tungsten sample. S3. Anneal the irradiated tungsten sample, and then perform TEM analysis on the annealed tungsten sample; determine the average radius r and volume fraction fv of the helium bubbles in the annealed tungsten sample from the TEM analysis results, and calculate the I value according to the following relationships 2 and 3. (2), (3), In the formula, r is the average radius of the helium bubble in the tungsten sample, in nm; V is the volume of the tungsten sample, in nm. 3 fv represents the volume fraction of the helium bubble; S4. Determine the recrystallization inhibition of the tungsten sample based on the values ​​of thresholds T and I.

[0007] The method of this invention can determine the recrystallization inhibition of tungsten samples by comparing the values ​​of threshold T and I, and proposes a new criterion for recrystallization inhibition. This can explain the recrystallization inhibition behavior when Zener resistance is not dominant in traditional studies, and provides a new basis for the study of helium plasma irradiation to inhibit tungsten recrystallization.

[0008] In some embodiments, in step S1, the tungsten sample includes at least one of tungsten metal or tungsten alloy.

[0009] In some embodiments, in step S1, the Ω is 3-5°μm. -1 The α is 0.3-0.4, and the θ m It is 10-20°.

[0010] In some embodiments, in step S2, the helium plasma irradiation treatment uses a plasma beam with a full width at half maximum (FWHM) of 10-25 mm and a peak particle flux of (1-5) × 10⁻⁶. 23 m-2 s -1 The ion bombardment energy is 30-80 eV, the average surface temperature is 850-900 K, and the cumulative peak particle fluence is (5-10) × 10⁻⁶. 26 m -2 .

[0011] In some embodiments, in step S3, the TEM analysis uses a focused ion beam to prepare a tungsten sample sheet with a thickness of 50-150 nm, an accelerating voltage of 20-200 kV during TEM testing, and a magnification of 200 k-500 k times during TEM testing.

[0012] In some embodiments, in step S3, the annealing temperature is the recrystallization temperature of the tungsten sample.

[0013] In some embodiments, when the tungsten sample is metallic tungsten, the recrystallization temperature is 1473-1673 K, and the annealing time is 10-180 min, preferably 15-60 min.

[0014] In some embodiments, the temperature of the annealing process is measured using a thermometer, which includes, but is not limited to, thermocouple thermometers, colorimetric thermometers, and infrared camera thermometers.

[0015] In some implementations, in step S4, when the T value and the I value satisfy the following relationship 4, the recrystallization nucleation process of the tungsten sample is suppressed, and the suppression is significant. I > T (4).

[0016] When the I value is greater than the T value, it indicates that the recrystallization nucleation process of tungsten is inhibited.

[0017] In some implementations, in step S4, when the T value and the I value satisfy the following relationship 5-6, the recrystallization nucleation of the tungsten sample is suppressed, and the suppression is relatively weak. T min ≤T≤T max (5), T min <I<T max (6), In the formula, T min Let T be the minimum value of T. max This is the maximum value of T.

[0018] When the I value is within the T value range, the recrystallization nucleation of tungsten is not significantly inhibited, and the recrystallization inhibition is not significant.

[0019] In some implementations, in step S4, when the T value and the I value satisfy the following relationship 7, the recrystallization nucleation process of the tungsten sample is not suppressed; I < T (7).

[0020] When the I value is less than the T value, the recrystallization nucleation process of tungsten is not inhibited, and recrystallization is uninhibited.

[0021] Compared with the prior art, the present invention has the following advantages: The method of the present invention proposes a new correlation for suppressing tungsten recrystallization by helium plasma irradiation: and By assessing the relationship between T-values ​​and I-values, this invention explains the evaluation of tungsten recrystallization inhibition in traditional studies where Zener drag is not dominant. It reveals a new mechanism for inhibiting recrystallization beyond the traditional helium bubble pinning of grain boundaries. This method provides a new pathway for future research on inhibiting tungsten recrystallization under helium plasma irradiation, enabling the prediction of tungsten material recrystallization behavior in fusion reactors. This allows for better prevention of damage caused by recrystallization of the divertor and first wall in fusion devices, ultimately leading to more accurate predictions of the fusion device's service life. Attached Figure Description

[0022] Figure 1 The diagram shows the EBSE analysis results. Inset (a) is the KAM diagram, and inset (b) is a schematic diagram of lattice rotation along three horizontal lines selected from KAM diagram (a), thus revealing the relationship between the lattice rotation angle and the distance along these lines. One of the horizontal lines is shown in the lower right corner of inset (a). The remaining two horizontal lines were added to verify the calculation results of the first line and are not shown in the diagram. Based on this diagram, the ratio of the change in lattice rotation angle to the distance in the tungsten sample can be obtained, thereby determining the crystal orientation gradient Ω of the tungsten sample, expressed as: Ω = .

[0023] Figure 2 This is a schematic diagram of the evolution of the tungsten sample's suppressed recrystallization process in Example 1. The figure shows a representative single grain, and the dashed lines in the grain represent the grain boundaries of subgrains. Figure 2 The illustration (a) shows the control group sample grains (without helium plasma irradiation), after which the subgrains grew normally after annealing; Figure 2 The illustration (b) shows a sample grain irradiated with helium plasma, with helium bubbles on its subsurface. After annealing, the helium bubbles pinned to the subgrain boundaries, inhibiting subgrain growth.

[0024] Figure 3 This is a schematic diagram of the calculation results for Example 1. Detailed Implementation

[0025] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, the test methods used in the embodiments and / or comparative examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0026] Example 1 A method for determining the inhibition of tungsten recrystallization includes the following steps: S1. Take a pure tungsten sample with a thickness of 1 mm and a length and width of 20 mm, and process it by mechanical equipment to grind and polish it so that the surface roughness Ra of the pure tungsten sample is less than 100 Å. The polished tungsten samples were then subjected to EBSD testing to obtain their KAM images. EBSD measurements were performed using a Zeiss Sigma 300 scanning electron microscope (SEM) equipped with an Oxford C-Nano detector, with a scanning voltage of 20 kV and a step size of 0.5–0.6 μm. Based on this EBSD data, the KAM images of the tungsten samples were automatically processed by AZtecCrystal, as shown in the following figures. Figure 1 As shown.

[0027] S2. The sample was placed in a cascaded arc plasma source pre-research platform (SPARROW) for helium plasma irradiation. The electron temperature and electron density were measured using a reciprocating Langmuir probe. The half-width at half-maximum (FWHM) of the plasma beam was approximately 20 mm, and the peak particle flux was approximately 2.4 × 10⁻⁶. 23 m -2 s -1 The ion bombardment energy was approximately 50 eV (achieved by applying a negative bias voltage to the target), the average surface temperature was 853 ± 39 K (dual-colorimetric pyrometer, model QKTRD 1075-1), and the cumulative peak particle fluence reached 8.64 × 10⁻⁶. 26 m -2 Ensure helium is injected to create helium bubbles in the tungsten sample, resulting in an irradiated tungsten sample.

[0028] S3. Perform TEM characterization on the irradiated tungsten sample. During sample preparation, a focused Ga... +Focused ion beam (FIB) extraction was employed in a Helios G4 UX dual-beam system to prepare site-specific cross-sectional TEM tungsten sample thin sections. This allowed for the preparation of electron transmission samples at grain boundaries where recrystallized grains met the original grains, facilitating the observation of helium bubbles at these boundaries. The experiment used a Ga⁺ ion beam with varying voltage and current for milling and thinning. When the thin section thickness was reduced to approximately 100 nm, the final process parameters were 2 kV / 10 pA. Transmission electron microscopy (TEM) imaging was performed using a Talos F200X scanning transmission electron microscope with an accelerating voltage ranging from 20 to 200 kV, adjusted via software, and observed and photographed at 245 kx magnification. The TEM images confirmed the presence of helium bubbles at the grain boundaries of the tungsten sample, exhibiting a near-spherical morphology. The radius and volume of the helium bubbles in the TEM images were analyzed using the ImageJ software package. For each experimental condition, multiple bright-field TEM images were analyzed to ensure statistical significance. Each measurement included all independent helium bubbles (approximately 100-500) in the TEM sample. Based on the assumption that the cross-section of each helium bubble is approximately circular, the radius of each bubble was determined, and the average helium bubble radius *r* and standard deviation were calculated based on all measurement data. The helium bubble volume fraction (f) was determined to be the proportion of the total volume of all helium bubbles in the tungsten sample to the total volume of the tungsten sample. V Assuming the bubbles are ideal spheres, the total volume of all measured helium bubbles is divided by the (total) volume V of the tungsten sample in the analytical region to obtain the helium bubble volume fraction (f). V V is calculated as follows: the two-dimensional observation area of ​​the TEM image multiplied by the thickness of the sheet determined by focused ion beam milling, approximately 100 nm.

[0029] The average radius of the helium bubbles in the tungsten sample at this time was r = 5.27 nm, and the calculated volume fraction of the helium bubbles was f. V The value was 0.61%; the tungsten sample at this time was considered as a tungsten sample in the unannealed state (annealing time was 0h).

[0030] S4. The irradiated tungsten samples were annealed at 1573 K four times, each time for 15 min. The temperature was measured using a dual-colorimetric thermometer during each annealing process. The annealing temperature was kept stable using rapid heating and cooling (approximately 1000 K min). -1 Electron beam annealing was used to avoid the influence of excessively long heating and cooling times on the time results; after each annealing experiment, samples were taken, and TEM tests and analyses were performed on the tungsten samples, with the test parameters being the sample preparation and test conditions in step S3 above.

[0031] TEM analysis was performed on the tungsten samples after each annealing treatment to determine the average radius r and volume fraction fv of the helium bubbles in the tungsten samples after each annealing treatment.

[0032] S5. Determine the recrystallization inhibition of tungsten samples based on the values ​​of threshold T and I: Determine the orientation gradient Ω, shape factor α, and critical orientation difference angle θm of the tungsten sample based on the relationship between the lattice rotation angle change and distance of the horizontal line in the KAM diagram of the tungsten sample. The orientation gradient Ω is defined as the ratio of the lattice rotation angle change to the distance; the shape factor α is a geometric constant used to correlate the area of ​​grain boundaries per unit volume with the grain or subgrain size D. When helium bubbles are present in the subsequently irradiated tungsten sample, and the volume fraction of helium bubbles fv < 0.05, α is 0.35; the critical orientation difference angle θm marks the transition from low-angle grain boundaries to high-angle grain boundaries, and θm is 10-15°; beyond this angle, this description is no longer applicable, and the energy tends to be constant, i.e., the energy of high-angle grain boundaries; when helium bubbles are present in the subsequently irradiated tungsten sample, and the volume fraction of helium bubbles fv < 0.05, θm is 15°, and the range of the threshold T is determined according to the following relationship 1. (1), In the formula, Ω represents the orientation gradient, with units of °um. -1 ; α is the shape factor; θ m The critical orientation difference angle, in degrees; In this embodiment, the orientation gradient Ω ranges from 3 to 5°μm. -1 Let the shape factor α = 0.35, θ m With a value of 15°, the lower threshold of T is calculated to be 0.0093, and the upper threshold of T is 0.0156, meaning the range of T is 0.0093-0.0156.

[0033] If nucleation occurs in a region with an orientation gradient of Ω, a large-angle orientation difference of θ is formed. m The required subgrain growth at the boundary is approximately θ m / Ω. If pinning results in the largest possible stable nucleus size D. lim (Defined as the minimum size at which a recrystallization nucleus can stably exist and begin to grow under a given second-phase particle distribution, i.e., a specific particle size and volume fraction.) If the size is smaller than the minimum size required for successful nucleation, then recrystallization nucleation is completely suppressed. Thus, a first-order approximation nucleation description can be used, which can be expressed as: (8).

[0034] Specifically, in this embodiment, after helium plasma irradiation, helium bubbles exist as second-phase particles in the tungsten sample. At this time, given the average radius r of a single helium bubble in the tungsten sample and the volume fraction fv of the helium bubbles in the tungsten sample, D... lim The following equation (9) can be used to determine the Zener-limited grain size: (9); in, The critical orientation difference angle is represented by α, with a recommended value of 15°; α represents the shape factor in... When the value is less than 0.05, a value of 0.35 is recommended. r is the average radius of the helium bubble, and fv is the volume fraction of the helium bubble in the tungsten sample.

[0035] The criterion can be obtained by combining equations 8-9: ; To facilitate better comparative analysis, I pairs were used. definition: (2), (3), In the formula, r is the average radius of the helium bubble, in nm; V is the volume of the tungsten sample, in nm. 3 fv represents the volume fraction of helium bubbles in the tungsten sample. r, V, and fv are obtained through TEM testing in step S3 above. r is the average radius of all helium bubbles counted in the TEM test, V is the volume of the tungsten sample corresponding to the helium bubble distribution area counted in the TEM test, and fv is the ratio of the total volume of all helium bubbles to the volume of the corresponding tungsten sample.

[0036] The value of I was calculated according to Equations 2 and 3, and the results are shown in Table 1. Table 1 TEM images show that there are very few helium bubbles on the high-angle grain boundaries after 15 min of annealing. This means that the inhibition of recrystallization after 15 min is not dominated by Zener resistance. Combined with EBSD data analysis, annealing for 15 min is a process that inhibits the nucleation of recrystallized grains and suppresses recrystallization.

[0037] At the same time, in order to observe more intuitively, with f V With r as the vertical axis and r as the horizontal axis, the threshold range is within the fv-r graph ( Figure 3 In the diagram, the threshold is displayed as an upper threshold line and a lower threshold line passing through the origin, and the range in between is the threshold range.

[0038] Combination Figure 2 Based on the data in Table 1, the degree of inhibition during recrystallization can be determined by the relationship between I and T. Figure 3 The point in the middle is the tungsten sample after annealing for 15-60 minutes. The values ​​show that after annealing for 15-45 minutes, the I value is above the threshold line, indicating that recrystallization is significantly inhibited. After annealing for 60 minutes, the I value is within the threshold range, and the inhibition effect is much weaker than before. This suggests that the recrystallization inhibition behavior is not dominated by Zener resistance caused by helium bubble pinning; rather, the helium bubble inhibits the nucleation of recrystallized grains, thereby inhibiting recrystallization. The results determined by the I and T values ​​are corroborated by the analysis results of TEM and EBSD data.

[0039] like Figure 2 This is the mechanism by which recrystallization is inhibited. Figure 2 The illustration (a) shows the control group sample grains, i.e., the tungsten sample that was not irradiated with helium plasma. After annealing, the subgrains grew normally without significant inhibition. Figure 2 The illustration (b) shows a sample grain irradiated with helium plasma, in which helium bubbles exist on the subsurface. After annealing, the helium bubbles pin the subgrain boundaries, inhibiting subgrain growth. This leads to a new inhibition mechanism where helium bubbles inhibit recrystallization by pinning subgrain boundaries.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for determining the inhibition of tungsten recrystallization, characterized in that, Includes the following steps: S1. The tungsten sample undergoes surface pretreatment, followed by EBSD analysis to obtain the KAM diagram. Based on the KAM diagram, the orientation gradient Ω, shape factor α, and critical orientation difference angle θ are determined. m And calculate and determine the range of the threshold T according to the following relationship 1; （1）， In the formula, Ω represents the orientation gradient, with units of °um. -1 α is the shape factor; θ m The critical orientation difference angle, in degrees; S2. The tungsten sample is subjected to helium plasma irradiation to create helium bubbles in the tungsten sample, resulting in an irradiated tungsten sample. S3. Anneal the irradiated tungsten sample, and then perform TEM analysis on the annealed tungsten sample. Determine the average radius r and volume fraction fv of the helium bubbles in the annealed tungsten sample based on the TEM analysis results, and calculate the I value according to the following relationships 2 and 3. （2）， （（3）， In the formula, r is the average radius of the helium bubble in the tungsten sample, in nm; V is the volume of the tungsten sample, in nm. 3 fv represents the volume fraction of the helium bubble; S4. Determine the recrystallization inhibition of the tungsten sample based on the values ​​of thresholds T and I.

2. The method for determining the inhibition of tungsten recrystallization as described in claim 1, characterized in that, In step S4, when the T value and I value satisfy the following relationship 4, the recrystallization nucleation process of the tungsten sample is suppressed; I > T (4).

3. The method for determining the inhibition of tungsten recrystallization as described in claim 1, characterized in that, In step S4, when the T value and I value satisfy the following relationship 5-6, the recrystallization nucleation of the tungsten sample is suppressed; T min ≤T≤T max (5), T min <I<T max (6), In the formula, T min Let T be the minimum value of T. max This is the maximum value of T.

4. The method for determining the inhibition of tungsten recrystallization as described in claim 1, characterized in that, In step S4, when the T value and I value satisfy the following relationship 7, the recrystallization nucleation process of the tungsten sample is not inhibited; I < T (7).

5. The method for determining the inhibition of tungsten recrystallization as described in claim 1, characterized in that, In step S1, the tungsten sample includes at least one of tungsten metal or tungsten alloy.

6. The method for determining the inhibition of tungsten recrystallization as described in claim 1, characterized in that, In step S1, Ω is 3-5°μm. -1 The α is 0.3-0.4, and the θ m It is 10-20°.

7. The method for determining the inhibition of tungsten recrystallization as described in claim 1, characterized in that, In step S2, during the helium plasma irradiation treatment, the full width at half maximum (FWHM) of the plasma beam is 10-25 mm, and the peak particle flux is (1-5) × 10⁻⁶. 23 m -2 s -1 The ion bombardment energy is 30-80 eV, the average surface temperature is 850-900 K, and the cumulative peak particle fluence is (5-10) × 10⁻⁶. 26 m -2 .

8. The method for determining the inhibition of tungsten recrystallization as described in claim 1, characterized in that, In step S3, the annealing temperature is the recrystallization temperature of the tungsten sample.

9. The method for determining the inhibition of tungsten recrystallization as described in claim 8, characterized in that, When the tungsten sample is metallic tungsten, the recrystallization temperature is 1473-1673K, and the annealing time is 10-180min.

10. The method for determining the inhibition of tungsten recrystallization as described in claim 1, characterized in that, In step S3, during the TEM analysis, a tungsten sample sheet is prepared using a focused ion beam. The thickness of the sample sheet is 50-150 nm, the accelerating voltage during TEM testing is 20-200 kV, and the magnification during TEM testing is 200 k-500 k times.

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