A method for determining a hot working window of a refractory high-entropy alloy containing a brittle grain boundary phase and a hot working method thereof

Abstract

The application discloses a method for determining a hot working window of a refractory high-entropy alloy containing a brittle grain boundary phase and a hot working method thereof, and belongs to the technical field of hot working processes of metal materials. The method for determining the hot working window of the refractory high-entropy alloy comprises the following steps: S1, obtaining a true stress-true strain curve; S2, calculating material constants α, n, Q and A under different true strains to obtain strain compensation activation energy Q ε ; S3, calculating power dissipation efficiency η and rheological instability parameter ξ based on a dynamic material model, constructing a power dissipation diagram and an instability diagram, superimposing and projecting the power dissipation diagram and the instability diagram, and obtaining a hot working diagram; and S4, identifying a crack sensitive area driven by a brittle granular or film-shaped brittle grain boundary phase through microstructure observation, and determining a stable and optimal hot working window. The application realizes determination of a stable hot working area and reduction of processing defects.

Description

Technical Field

[0001] This invention relates to the field of hot working technology for metallic materials, specifically to a method for determining the hot working window of a refractory high-entropy alloy containing brittle grain boundary phases and the hot working method thereof. Background Technology

[0002] Refractory high-entropy alloys have broad application prospects in aerospace and nuclear industries due to their excellent high-temperature strength and thermal stability. However, because these alloys typically contain high-melting-point elements and brittle intermetallic compounds (such as Al-Zr phase) in their microstructure, their hot deformation behavior is extremely complex, making them highly susceptible to cracking during hot working. Currently, traditional dynamic material models (DMMs) struggle to identify pseudo-stable regions caused by brittle grain boundary phases in their hot working diagrams, and they do not consider the impact of the dissolution and cracking behavior of brittle grain boundary phases on hot working stability. Consequently, even when deformation is performed within the "stable region" of the working diagram in actual production, microcracks may still appear inside the material, severely limiting the engineering applications of refractory high-entropy alloys. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a method for determining the hot working window of refractory high-entropy alloys containing brittle grain boundary phases and a hot working method thereof, which solves the technical problem that traditional hot working diagrams are difficult to identify the pseudo-stable region induced by brittle grain boundary phases, thereby achieving precise control of alloy microstructure evolution and effectively avoiding processing defects.

[0004] To achieve the above technical objectives, the present invention provides a method for determining the hot working window of a refractory high-entropy alloy, wherein the alloy is a refractory high-entropy alloy containing brittle grain boundary phases, preferably an Al-Nb-Ta-Ti-V-Zr system alloy, comprising the following steps: S1, at a temperature of 1173~1473 K and a strain rate of 10 -3 ~1 s -1 Multiple isothermal compression tests were conducted on the alloy within the specified range to obtain true stress-true strain curves. S2. Based on the hyperbolic sine Arrhenius equation, a strain-compensated constitutive model is established. The material constants α, n, Q, and A under different true strains are calculated, and the strain-compensated activation energy Q is obtained. ε ; S3. Based on the dynamic material model, calculate the power dissipation efficiency η and the rheological instability parameter ξ, and construct the power dissipation diagram and the instability diagram; superimpose the power dissipation diagram and the instability diagram to obtain the initial thermal processing diagram; S4. By observing the microstructure, identify the crack-sensitive areas driven by brittle granular or film-like grain boundary phases. Based on the distribution characteristics of the brittle grain boundary phases, correct the initial hot working diagram and determine the unstable area, stable hot working area, and optimal hot working window.

[0005] In any implementation, in step S2, the strain compensation constitutive model uses a polynomial to fit the relationship between the material constant and the true strain ε:

[0006] Where Q is in kJ / mol, and the strain compensation activation energy Qε varies with true strain.

[0007] In any implementation, the formulas for calculating the power dissipation efficiency η and the rheological instability parameter ξ in step S3 are as follows:

[0008] Where m is the strain rate sensitivity coefficient, obtained through the relationship between rheological stress and strain rate, and σ is the rheological stress.

[0009] In any implementation, in step S4, the unstable region includes: First unstable region: In this region, the brittle grain boundary phase does not dissolve due to low temperature and high strain rate, which leads to the formation of three-pronged grain boundary intersection cracks, wedge cracks and longitudinal surface cracks; Second unstable region: In this region, the brittle grain boundary phase lacks sufficient dissolution time due to excessively high strain rate, and the stress concentration at the interface triggers intergranular cracking.

[0010] In any implementation, the method further includes the following after step S4: S5. Combining the peak power dissipation efficiency with the defect-free microstructure characteristics, and combining the power dissipation efficiency with the evolution characteristics of brittle grain boundary phases, stability analysis is performed to determine whether the high η region corresponds to a reduction in brittle grain boundary phases.

[0011] In any embodiment, in step S5, within the optimal heat treatment window, the high η region corresponds to a portion of the dynamic recrystallization structure.

[0012] In any implementation, in step S5, the optimal heat treatment window is determined to be located in the high temperature and low strain rate region.

[0013] In any implementation, the method further includes the following after step S5: Electron backscatter diffraction was used to analyze the grain boundary stress concentration distribution of hot-compressed specimens, verifying the influence of stress concentration at grain boundaries and brittle grain boundary phase dissolution on hot working stability.

[0014] In addition, the present invention also proposes a thermomechanical processing method for refractory high-entropy alloys. After determining the optimal hot working window using the above method, the alloy is subjected to isothermal compression deformation within the optimal hot working window, and the deformation amount is not less than 50%.

[0015] In any embodiment, within the optimal hot working window, the power dissipation efficiency η of the alloy reaches its highest value, the microstructure exhibits partial dynamic recrystallization characteristics, the brittle grain boundary phase is completely dissolved, and macroscopic and microscopic processing defects are eliminated; and / or, the alloy is subjected to homogenization annealing treatment before hot working, with an annealing temperature of 1100-1200℃ and a holding time of ≥24 h, followed by furnace cooling.

[0016] Compared with existing technologies, the beneficial effects of this invention include: the determination method proposed in this invention has high accuracy, strong reliability, and broad guidance. The model predictions and experimental values ​​show high consistency. It successfully identifies spurious stable regions in traditional hot working diagrams, avoiding misjudgments by traditional diagrams and achieving precise control of alloy microstructure evolution and effective avoidance of processing defects. It provides a general hot working optimization method for refractory high-entropy alloys containing brittle grain boundary phases. Attached Figure Description

[0017] Figure 1 This is the homogenized annealed Al state of Embodiment 1 of the present invention. 0.5 NbTa 0.8 Ti 1.5 V 0.2 XRD patterns and SEM backscattered electron images of Zr RHEA reveal the matrix structure and brittle second-phase grain boundaries; among which Figure 1 (a) is the XRD pattern. Figure 1 (b) is a SEM backscattered electron image.

[0018] Figure 2 The true stress-true strain curves and peak stress variation diagrams of the alloy in Example 2 of this invention at different temperatures and strain rates are shown.

[0019] Figure 3 This is a linear fitting graph of the alloy of Embodiment 2 of the present invention based on the hyperbolic sine Arrhenius model, including the relationships lnε˙ -lnσ, lnε˙ -σ, lnε˙ -ln[sinh(ασ)], ln[sinh(ασ)]-1 / T and lnZ-ln[sinh(ασ)].

[0020] Figure 4 This is a comparison graph of the strain-compensated constitutive model prediction and experimental values ​​of the alloy in Example 2 of the present invention, showing a high degree of consistency (R2=0.9851).

[0021] Figure 5 This is a hot working diagram and stable region distribution of the alloy in Example 2 of the present invention under different strains (ε=0.4, 0.5, 0.6).

[0022] Figure 6These are EBSD band contrast diagrams and phase distribution diagrams of the alloy under different deformation conditions in Example 2 of the present invention, showing the evolution process of the gradual dissolution of the brittle grain boundary phase.

[0023] Figure 7 This is an EBSD analysis of the unstable crack region of the alloy in Example 2 of the present invention, including a phase distribution map of the crack region.

[0024] Figure 8 These are macroscopic and microscopic images of the alloy under optimal hot working conditions in Example 3 of this invention. Detailed Implementation

[0025] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0026] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0027] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0028] This specific embodiment provides a method for determining the hot working window of a refractory high-entropy alloy, wherein the alloy is a refractory high-entropy alloy containing a brittle grain boundary phase, and the refractory high-entropy alloy containing the brittle grain boundary phase is an Al-Nb-Ta-Ti-V-Zr system alloy, and the alloy is Al 0.5 NbTa 0.8 Ti 1.5 V 0.2 Zr refractory high-entropy alloy, including the following steps: S1, at a temperature of 1173~1473 K and a strain rate of 10 -3 ~1 s -1 Multiple isothermal compression tests were conducted on the alloy within the specified range to obtain true stress-true strain curves. S2. Based on the hyperbolic sine Arrhenius equation, a strain-compensated constitutive model is established, and the material constants α, n, Q, and A under different true strains are calculated to obtain the strain-compensated activation energy Qε. The strain-compensated constitutive model uses a polynomial fit to the relationship between the material constant and the true strain ε:

[0029] Where Q is in kJ / mol, and the strain compensation activation energy is Q0. ε Changes should be made according to actual circumstances; S3. Based on the dynamic material model, calculate the power dissipation efficiency η and the rheological instability parameter ξ, and construct the power dissipation map and the instability map; superimpose the power dissipation map and the instability map to obtain the initial thermal processing map, wherein the region where ξ<0 is determined as the instability region; The formulas for calculating the power dissipation efficiency η and the rheological instability parameter ξ are as follows:

[0030] Where m is the strain rate sensitivity coefficient, obtained through the relationship between rheological stress and strain rate, and σ is the rheological stress; S4. Through microscopic observation, identify crack-sensitive regions driven by brittle granular or film-like grain boundary phases. Based on the distribution characteristics of the brittle grain boundary phases, correct the initial hot working diagram to determine the unstable region, stable hot working region, and optimal hot working window. The unstable region includes: First instability zone: Temperature 1173~1350 K, strain rate 10 -2.5 ~1 s -1 In this region, the brittle grain boundary phase did not dissolve due to the low temperature and high strain rate, which led to the formation of triangular grain boundary intersection cracks, wedge-shaped cracks and longitudinal surface cracks. Second instability zone: Temperature 1400~1473 K, strain rate 10 -1.5 ~1 s -1In this region, the excessively high strain rate leads to insufficient dissolution time for the brittle grain boundary phase, and the stress concentration at the interface causes intergranular cracking.

[0031] In some embodiments, the method further includes the following after step S4: S5. Combining the peak power dissipation efficiency with the defect-free microstructure characteristics, and combining the power dissipation efficiency with the evolution characteristics of brittle grain boundary phases, a stability analysis is performed to determine whether the high-η region corresponds to a reduction in brittle grain boundary phases. Within the optimal heat treatment window, the high-η region corresponds to a portion of the dynamic recrystallization structure. The optimal heat treatment window is determined to be located in a high-temperature, low-strain-rate region. In some embodiments, the optimal heat treatment window is determined to be a temperature of 1373~1473 K and a strain rate of 10... -3 ~10 -1.5 s -1 .

[0032] In some embodiments, the method further includes the following after step S5: Electron backscatter diffraction was used to analyze the grain boundary stress concentration distribution of hot-compressed specimens, verifying the influence of stress concentration at grain boundaries and brittle grain boundary phase dissolution on hot working stability.

[0033] This specific embodiment also proposes a thermomechanical processing method for refractory high-entropy alloys. After determining the optimal hot working window using the above method, the alloy is subjected to isothermal compression deformation within the optimal hot working window, with a deformation amount of not less than 50%. Within this optimal hot working window, the power dissipation efficiency η of the alloy reaches a maximum value of 45%–62%, the microstructure exhibits partial dynamic recrystallization characteristics, and the brittle grain boundary phase is completely dissolved, eliminating macroscopic and microscopic processing defects. And / or, the alloy undergoes homogenization annealing before hot working at an annealing temperature of 1100–1200℃ for a holding time of ≥24 h, followed by furnace cooling. Further, the alloy undergoes homogenization annealing before hot working at an annealing temperature of 1200℃ for a holding time of not less than 24 h, followed by furnace cooling, to obtain an equiaxed grain structure with an average grain size of approximately 150 μm.

[0034] This invention provides a method for determining the hot working window of refractory high-entropy alloys containing brittle grain boundary phases. Addressing the problem that the brittle Al-Zr phase at grain boundaries in the Al-Nb-Ta-Ti-V-Zr BCC+B2 dual-phase alloy causes the failure of traditional power dissipation efficiency (η) assessments, this invention establishes a strain-compensated Arrhenius constitutive model, constructs a three-dimensional processing map based on a Dynamic Model (DMM), and establishes a three-dimensional correlation diagram between η, dynamic recrystallization fraction, and brittle grain boundary phase fraction. This reveals the decoupling mechanism between high η values ​​and incomplete recrystallization, accurately determining the optimal hot working window as 1373~1473 K and 10 -3 ~10 -1.5 s -1This method avoids misjudgment of η in multiphase alloys and provides a reliable process design basis for defect-free thermomechanical processing of RHEA containing brittle grain boundary phases.

[0035] In the hot deformation process of refractory high-entropy alloys containing brittle grain boundary phases, the dissolution and cracking behavior of the brittle Al-Zr phase severely interferes with the reliability of traditional hot working diagrams based on dynamic material models. High values ​​of conventional power dissipation efficiency η may correspond to crack propagation or phase dissolution endothermic processes, rather than microstructure homogenization. This invention addresses how to decouple various energy dissipation mechanisms of η and establishes a method for constructing working diagrams that can distinguish between "true stable regions" and "false stable regions."

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] In this invention, the terms "some embodiments," "this embodiment," and examples are used to describe a subset of all possible embodiments. However, it is understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0038] If the application documents contain similar descriptions such as "first / second", the following explanation shall be added: In the following description, the terms "first / second / third" are used only to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0039] In this embodiment, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, object A and / or object B can represent three situations: object A exists alone, object A and object B exist simultaneously, and object B exists alone.

[0040] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0041] Example 1 According to atomic ratio Al 0.5 NbTa 0.8 Ti 1.5 V0.2 Zr was prepared with high-purity (>99.9%) raw materials, and alloy ingots were prepared using the existing induction suspension melting method. The ingots were repeatedly melted five times to ensure uniform composition. Cylindrical samples of φ8mm × 12mm were cut from the ingots using wire cutting. The samples were vacuum-sealed in quartz tubes and homogenized in a tube furnace at 1200℃ for 24 h, followed by furnace cooling.

[0042] XRD analysis of homogenized alloys ( Figure 1 (a) shows that it consists of a disordered BCC (A2) phase and an ordered B2 phase. Due to lattice parameter mismatch, there is a distinguishable peak position shift between the (110) peak of BCC and the (110) peak of B2. SEM-BSE observation ( Figure 1 (b) shows an equiaxed crystal structure with an average grain size of about 150 μm. Continuous and coarse dark-contrast Al-Zr phases are distributed at the grain boundaries, and their chemical formula is identified as Al3Zr5.

[0043] Example 2 This embodiment proposes a method for determining the hot working window of refractory high-entropy alloys containing brittle grain boundary phases, including the following steps: S1, at a temperature of 1173~1473 K and a strain rate of 10 -3 ~1 s -1 Multiple isothermal compression tests were conducted on the alloy within the specified range to obtain true stress-true strain curves. Specifically, isothermal compression tests were performed on the alloy ingot prepared in Example 1 on a Gleeble-3500 thermal simulator at deformation temperatures of 900℃, 1000℃, 1100℃, and 1200℃ (i.e., 1173 K, 1273 K, 1373 K, and 1473 K) and strain rates of 0.001, 0.01, 0.1, and 1 s⁻¹, respectively. -1 The deformation was 50%. The sample was heated to the target temperature at 10℃ / s, held for 3 min, and immediately water-quenched after compression to preserve the high-temperature microstructure. The true stress-true strain curve of the alloy ingot was obtained. Figure 2 All exhibited an initial elastic stage, a significant stress drop, and subsequent continuous rheological softening characteristics, indicating the activation of dynamic recrystallization. Based on the Sellars-Tegart hyperbolic sine Arrhenius equation, the peak stress was used to calculate α=0.00273, n1=6.7299, β=0.01839, apparent activation energy Q≈416 kJ / mol, and structure factor A=6.25987×10⁻⁶. 14 ; S2. Establishing a strain-compensated constitutive model based on the hyperbolic sine Arrhenius equation ( Figure 3The material constants α, n, Q, and A under different true strains are calculated to obtain the strain compensation activation energy Qε. The strain compensation constitutive model uses a fifth-order polynomial to fit the relationship between the material constants and the true strain ε.

[0044] Where Q is in kJ / mol, and the strain compensation activation energy Qε increases with strain in the range of 304~324 kJ / mol; Specifically, strain compensation is further introduced, and rheological stress data are extracted at intervals of 0.05 within the true strain range of 0.1 to 0.65. A fifth-order polynomial is used to fit the relationship between α, n, Q, lnA, and ε. The strain compensation activation energy Q is... ε The increase from 304 kJ / mol to 324 kJ / mol reflects the rise in the thermal activation barrier during the dynamic equilibrium stage, dominated by work hardening. The stress exponent n remained stable between 3.66 and 3.85, while α increased from 0.0041 to 0.0061, indicating enhanced stress sensitivity. The coefficient of determination R between model predictions and experimental values... 2 Reaching 0.9851 ( Figure 4 This verified the reliability of the model.

[0045] S3. Based on the dynamic material model, calculate the power dissipation efficiency η and the rheological instability parameter ξ, and construct a three-dimensional power dissipation diagram and a three-dimensional instability diagram; superimpose the three-dimensional power dissipation diagram and the three-dimensional instability diagram to obtain the thermal processing diagram; The formulas for calculating the power dissipation efficiency η and the rheological instability parameter ξ are as follows:

[0046] Where m is the strain rate sensitivity coefficient, obtained by comparing lnσ and lg ε The relationship between ˙ and σ is obtained by cubic spline fitting, where σ is the rheological stress; Specifically, based on the DMM model, lgσ-lg is fitted using cubic splines. ε The strain rate sensitivity coefficient m is obtained from the relationship, and then the power dissipation efficiency η and the instability parameter ξ are calculated. Three-dimensional instability diagrams and power dissipation diagrams are constructed at strains ε=0.4, 0.5, and 0.6, respectively. Figure 5 The heat treatment diagram is obtained by superimposing the images. Figure 5 ).

[0047] S4. Through microscopic observation, identify crack-sensitive regions driven by brittle granular or film-like Al-Zr grain boundary phases, and divide the heat treatment diagram into unstable regions, low-energy consumption regions, stable regions, and optimal heat treatment windows; the heat treatment diagram shows two main unstable regions: Region A (first unstable region): 1173~1350 K, 10 -2.5 ~1 s-1 η = 1%~27%. The samples exhibited longitudinal surface cracks (caused by circumferential tensile stress resulting from drum-shaped deformation), wedge-shaped cracks at the intersection of three grain boundaries (caused by grain boundary sliding incoordination and vacancy accumulation), and 45° shear cracks on the end face (induced by maximum shear stress due to frictional constraint). Region B (second instability region): 1400~1473 K, 10 -1.5 ~1 s -1 η = 20%~30%. Due to the excessively high strain rate, the brittle Al-Zr phase lacks sufficient dissolution time, and the interfacial stress concentration exceeds the grain boundary bonding strength, initiating intergranular cracking. The optimal hot working zone is 1373~1473 K, with a strain rate of 10... -3 ~10 -1.5 s -1 η=45%~62%, with no macroscopic or microscopic defects.

[0048] EBSD analysis showed that within the optimal window, the alloy formed a necklace-like fine-grained structure along the original grain boundaries, with recrystallized grains randomly oriented, while retaining deformation texture within the grains. <001> or <111> (Parallel compression axis). The GND density map shows a high density of geometrically necessary dislocations at the grain boundaries, providing microscopic evidence for the dislocation climb activation energy and directly supporting Q. ε The physical rationality of =304~324 kJ / mol.

[0049] Phase distribution diagram ( Figure 6 This reveals that under low-temperature, high-speed conditions (such as 900℃ / 1 s), -1 At grain boundaries, the Al-Zr phase maintains a continuous network; however, with increasing temperature and decreasing strain rate, the Al-Zr phase gradually fractures and dissolves. Within the optimal heat treatment window (e.g., 1100℃ / 0.01 s), the Al-Zr phase exhibits this characteristic. -1 Within this area, the grain boundary phase essentially disappears.

[0050] High-resolution EBSD analysis of cracks in the unstable zone ( Figure 7 The results indicate that the crack path coincides with the Al-Zr phase space, the GND density increases sharply at the crack tip, and the orientation mismatch between hard-oriented grains (SF<0.3) and soft-oriented grains (SF>0.4) leads to strain localization, promoting crack initiation. Within the optimal hot working window, the SF distribution becomes more uniform, the GND density decreases, and crack formation is effectively suppressed.

[0051] In the optimal window (1473 K / 10) -3 s -1Within this region, the high η region corresponds only to partial dynamic recrystallization, far lower than the complete recrystallization level of single-phase BCC alloys (such as MoNbHfZrTi) at similar η levels. Establishing a three-dimensional correlation diagram between η-DRX fraction and Al-Zr phase fraction reveals that the η peak occurs synchronously with the complete dissolution of the Al-Zr phase.

[0052] This phenomenon indicates that the dissolution of brittle grain boundary phases affects power dissipation behavior. Therefore, a high η value and a high η region do not necessarily correspond to a stable hot-worked region.

[0053] Correlation analysis confirmed that the high η value in Region E is indeed accompanied by the complete dissolution of the brittle phase, eliminating the pseudo-stable regions (with grain boundary cracks induced by grain boundary phases) in Regions C and D, thus determining the stable hot-working regions.

[0054] Example 3 The optimal heat treatment window (1373~1473 K, 10) determined in Example 2 was adopted. -3 ~10 -1.5 s -1 ), for Al 0.5 NbTa 0.8 Ti 1.5 V 0.2 Zr RHEA was subjected to isothermal compression deformation with a deformation of 50%. The processed sample showed no macroscopic cracks, no surface cracks, and no grain boundary micro-cracks. Figure 8 Microscopic analysis showed that the brittle Al-Zr phase at the grain boundaries had completely dissolved, forming a necklace-like partially recrystallized heterostructure, exhibiting partial dynamic recrystallization characteristics. No obvious crack defects were observed during hot working.

[0055] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for determining the hot working window of a refractory high-entropy alloy containing brittle grain boundary phases, characterized in that, The alloy is a refractory high-entropy alloy containing brittle grain boundary phases, and includes the following steps: S1, at a temperature of 1173~1473 K and a strain rate of 10 -3 ~1 s -1 Multiple isothermal compression tests were conducted on the alloy within the specified range to obtain true stress-true strain curves. S2. Based on the hyperbolic sine Arrhenius equation, a strain-compensated constitutive model is established, and the material constants α, n, Q, and A under different true strains are calculated to obtain the strain-compensated activation energy Qε. S3. Based on the dynamic material model, calculate the power dissipation efficiency η and the rheological instability parameter ξ, and construct the power dissipation diagram and the instability diagram; superimpose the power dissipation diagram and the instability diagram to obtain the initial thermal processing diagram; S4. By observing the microstructure, identify the crack-sensitive areas driven by brittle granular or film-like grain boundary phases, and correct the initial hot working diagram based on the distribution characteristics of the brittle grain boundary phases to determine the unstable area, stable hot working area and optimal hot working window. The process after step S4 also includes: S5. Combining the peak power dissipation efficiency with the defect-free microstructure characteristics, and combining the power dissipation efficiency with the brittle grain boundary phase evolution characteristics, a stability analysis is performed to determine whether the high η region corresponds to a reduction in brittle grain boundary phases; in step S5, within the optimal hot working window, the high η region corresponds to a portion of the dynamic recrystallization structure; in step S5, it is determined that the optimal hot working window is located in the high temperature and low strain rate region.

2. The method for determining the heat treatment window according to claim 1, characterized in that, In step S2, the strain compensation constitutive model uses a polynomial fitting to fit the relationship between the material constant and the true strain ε: Where ε is the true strain, Q is in kJ / mol, and the strain compensation activation energy is Q0. ε It adapts to changes in reality.

3. The method for determining the heat treatment window according to claim 1, characterized in that, In step S3, the formulas for calculating the power dissipation efficiency η and the rheological instability parameter ξ are as follows: Where m is the strain rate sensitivity coefficient, obtained through the relationship between rheological stress and strain rate, and σ is the rheological stress; And / or, in step S4, the unstable region includes: First unstable region: In this region, the brittle grain boundary phase does not dissolve due to low temperature and high strain rate, which leads to the formation of three-pronged grain boundary intersection cracks, wedge cracks and longitudinal surface cracks; Second unstable region: In this region, the brittle grain boundary phase lacks sufficient dissolution time due to excessively high strain rate, and the stress concentration at the interface triggers intergranular cracking.

4. The method for determining the heat treatment window according to claim 1, characterized in that, The process after step S5 also includes: Electron backscatter diffraction was used to analyze the grain boundary stress concentration distribution of hot-compressed specimens, verifying the influence of stress concentration at grain boundaries and brittle grain boundary phase dissolution on hot working stability.

5. The method for determining the heat treatment window according to claim 1, characterized in that, The refractory high-entropy alloy containing brittle grain boundary phases is an Al-Nb-Ta-Ti-V-Zr system alloy.

6. The method for determining the heat treatment window according to claim 5, characterized in that, The Al-Nb-Ta-Ti-V-Zr system alloy is Al 0.5 NbTa 0.8 Ti 1.5 V 0.2 Zr.

7. A thermomechanical processing method for a refractory high-entropy alloy, characterized in that, After determining the optimal hot working window using the method described in any one of claims 1 to 6, the alloy is subjected to isothermal compression deformation within the optimal hot working window.

8. The thermomechanical processing method for refractory high-entropy alloys according to claim 7, characterized in that, Within this optimal hot working window, the power dissipation efficiency η of the alloy reaches its highest value, the microstructure exhibits partial dynamic recrystallization characteristics, and the brittle grain boundary phase is completely dissolved, eliminating macroscopic and microscopic processing defects; and / or, the alloy is subjected to homogenization annealing treatment before hot working, with an annealing temperature of 1100-1200℃ and a holding time of ≥24 h, followed by furnace cooling.

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