A method for analyzing strain-induced supersaturation solid solution of immiscible alloy system based on hybrid entropy evolution

Abstract

The application discloses a strain-induced supersaturated solid solution analysis method for a non-miscible alloy system based on mixed entropy evolution, and the method comprises the following steps: for a target A-B binary alloy, a mixed entropy-component relationship diagram of the target A-B binary alloy is drawn; the average component and the initial equilibrium phase component point of the target A-B binary alloy are calibrated in the diagram; based on the increase of the mixed degree of the entropy generation driving force, the two-phase components are predicted to evolve in the entropy increase direction during a severe plastic deformation process, until a single-phase supersaturated solid solution is formed. Based on the irreversible thermodynamic principle, the severe plastic deformation process is defined as a continuous external entropy generation source for driving the evolution of the system, through the analysis of the dynamic competition mechanism of element mixing and element demixing dominated by the entropy generation source, the formation mechanism of the supersaturated solid solution is revealed, and the application provides a universal theoretical tool for understanding and predicting the supersaturated solid solution behavior of the non-miscible alloy system under the severe plastic deformation.

Description

Technical Field

[0001] This invention belongs to the field of materials science and technology, specifically relating to a strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution. Background Technology

[0002] Strain-induced supersaturated solid solution refers to the phenomenon in binary alloys where one phase completely dissolves into the other under strain, forming a chemically disordered single-phase solid solution. Although this phenomenon is relatively common in experiments, its formation mechanism remains highly controversial. Traditionally, alloys with negative enthalpy of mixing are considered to have a strong tendency for spontaneous mixing due to the exothermic mixing process, easily achieving atomic-level mixing under strain; essentially, this is a spontaneous transformation of the system towards thermodynamic equilibrium. However, with the development of severe plastic deformation (SPD) technology, the high strain and strain rate conditions achieved show that even binary alloys with positive enthalpy of mixing can form single-phase supersaturated solid solutions, a phenomenon beyond the explanation of traditional enthalpy of mixing theory. Therefore, two other viewpoints have been proposed: one is the atomic scattering factor viewpoint, which posits that the volume fraction of low scattering factor phases gradually decreases while the volume fraction of high scattering factor phases gradually increases during SPD; the other is the equivalent temperature viewpoint, which equates the system energy increase caused by SPD to a heat treatment effect under certain high-temperature conditions. While both perspectives can explain some experimental phenomena, they each have limitations. For example, the atomic scattering perspective can explain the formation of a single-phase supersaturated solid solution of Ti (high scattering factor) after adding a small amount of Mg (low scattering factor) to Ti (high scattering factor) via SPD, but it cannot explain the opposite phenomenon of forming a single-phase supersaturated solid solution of Mg after adding a small amount of Ti to Mg. Similarly, the equivalent temperature perspective can explain the solid solution behavior of small amounts of solute based on equilibrium phase diagrams, but it struggles to explain the phenomenon where the supersaturated solid solubility exceeds the maximum solubility on the equilibrium phase diagram.

[0003] Therefore, neither the atomic scattering factor nor the equivalent temperature perspective can provide a universal and internally consistent theoretical framework, which directly restricts the ability to actively design and systematically predict SPD-induced supersaturated solid solution processes. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing a strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on the evolution of mixing entropy. This method, based on the principle of irreversible thermodynamics, defines the intense plastic deformation process as a continuous external entropy source driving the system's evolution. By analyzing the dynamic competition mechanism of element mixing and demixing dominated by this entropy source, the formation mechanism of supersaturated solid solutions is revealed, providing a universal theoretical tool for understanding and predicting the nonequilibrium phase transformation of immiscible alloy systems under intense plastic deformation.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution, characterized in that the method includes the following steps: Step 1: For the target AB binary alloy, calculate and plot the mixing entropy-composition relationship graph with the concentration of component B as the horizontal axis and the mixing entropy as the vertical axis using the mixing entropy formula; Step 2: On the mixing entropy-composition relationship diagram drawn in Step 1, mark the average composition line of the target AB binary alloy, as well as the composition points corresponding to phase A and phase B under the initial equilibrium state, to obtain the calibrated mixing entropy-composition relationship diagram; Step 3: Based on the principle of non-equilibrium thermodynamics, the intense plastic deformation process is defined as a continuous external entropy generation source of the target alloy, and it is determined that this entropy generation source provides a driving force for the mixing process, promoting the continuous increase of the mixing degree. Step 4: On the calibrated mixing entropy-composition relationship diagram obtained in Step 2, based on the effect of the driving force in Step 3 on promoting the increase of mixing degree, describe and predict the composition evolution of the two phases of the target AB binary alloy under the action of severe plastic deformation process: that is, the composition of phase A and phase B evolves in the direction of increasing mixing entropy until one phase dissolves and finally forms a single-phase supersaturated solid solution.

[0006] In practical research and engineering applications, true thermodynamic equilibrium states are rare; most problems encountered are non-equilibrium thermodynamic problems. Within this framework, the role of entropy undergoes a fundamental transformation: it is no longer merely a state function characterizing the system's state, but through the concept of entropy generation, it becomes a fundamental physical quantity describing the direction and irreversibility of system evolution. In the SPD process of alloys, the dynamic competition of opposing mechanisms leads to the evolution of the system structure. For example, dislocation multiplication and dislocation annihilation are a pair of competing mechanisms. During plastic deformation, dislocation multiplication leads to a gradual increase in dislocation density, while... The increased dislocation density, in turn, promotes the increase of the dislocation annihilation rate. During this process, the dislocation annihilation rate gradually approaches the dislocation multiplication rate. When the two rates are equal, the dislocation density in the alloy reaches a constant and no longer changes with time. For the strain-induced supersaturated solid solution process involved in this application, element mixing and element demixing are a pair of competing mechanisms that dominate structural evolution. According to irreversible thermodynamics, for a binary immiscible alloy in equilibrium, the element mixing rate is zero, and the element demixing rate is also zero. Therefore, the mixing entropy of each constituent phase remains constant, i.e., close to 0. This leads to the alloy phase composition... Corresponding to the equilibrium phase composition; when SPD occurs, the externally input mechanical deformation, through irreversible processes such as dislocation slip, becomes a continuous source of entropy generation (σ>0), providing a strong, non-equilibrium mixing driving force. This leads to a significant increase in the element mixing rate, causing an increase in the phase mixing entropy, thus causing the phase to deviate from equilibrium. At the same time, according to irreversible thermodynamics, the continuous advancement of the element mixing process, i.e., deviating from the equilibrium state, also increases the thermodynamic driving force of its reverse process (element demixing) (e.g., chemical potential gradient), thereby leading to an increase in the separation rate, just like an increase in dislocation density. Just as the driving force for annihilation increases, as long as SPD continues, the mixing driving force maintained by the external entropy source will always dominate. This relationship ensures that the rate of element demixing cannot exceed the rate of element mixing, thereby causing the degree of element mixing, i.e., the continuous increase of mixing entropy. Specifically, in the immiscible AB binary alloy system, this process is manifested as: strain, as the external entropy source, continuously drives the transport of B solute atoms to the A phase and the transport of A solute atoms to the B phase. Macroscopically, this is manifested as the gradual increase of the concentration of B solute atoms in the A phase and the gradual increase of the concentration of A solute atoms in the B phase.

[0007] Based on the above mechanism, this invention proposes a strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution. This method is for immiscible binary alloy systems of A and B, using the atomic percentage of component B. X-axis, mixed entropy Plot the mixing entropy-composition relationship diagram with the Y-axis as the axis. Mark the average composition line of the target AB binary alloy on the diagram. For the AB binary alloy in its initial equilibrium state, the composition points of the A and B phases are located at opposite ends of the diagram. Figure 1The B content in phase A is extremely low, and the A content in phase B is also extremely low. This causes the mixing entropy of both phases A and B to approach zero. When SPD is applied to the target AB binary alloy, the composition of phases A and B evolves along the mixing entropy curve in the direction of increasing mixing entropy. Specifically, the concentration of B atoms in phase A gradually increases, and the concentration of A atoms in phase B also gradually increases. When phase A reaches the average composition of the alloy, according to the lever law, phase B completely dissolves, and the system evolves into a single-phase supersaturated solid solution of phase A.

[0008] The above-mentioned strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution is characterized in that the mixed entropy formula in step one is: ,in, S The entropy of mixing for a single phase, and These represent the atomic percentages of atoms A and B in this phase, respectively. The gas constant is 8.314 J / (mol·K). The mechanism proposed in this invention is based on the increase of mixing entropy to determine the evolution of phase composition, so the correspondence between mixing entropy and composition is required. Therefore, the mixing entropy formula and mixing entropy diagram are introduced.

[0009] The aforementioned strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution is characterized in that, in the average composition of the alloy described in step two, the atomic percentage of component B is not greater than 50%. In the target AB binary alloy of this invention, there is always one element with a content of not less than 50%, and another element with a content of not more than 50%. The element with a content less than 50% is directly designated as element B, because subsequent analyses are based on the case where the content of element B is less than 50%. If the content of element B is greater than 50%, then the names of A and B are interchanged, i.e., A becomes B, and B becomes A.

[0010] The above-mentioned strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on the evolution of mixing entropy is characterized in that the driving force in step three originates from the entropy generated by external mechanical deformation during intense plastic deformation. This driving force dominates the dynamic competition between element mixing and element demixing, and makes the element mixing process dominant.

[0011] The above-mentioned strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution is characterized in that the composition evolution path in step four is as follows: the concentration of B atoms in phase A increases synchronously with the concentration of A atoms in phase B.

[0012] The above-mentioned strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution is characterized in that the determination of the evolution endpoint state in step four is based on the following: when the composition of phase A reaches the average composition of the alloy, according to the lever law, phase B completely dissolves, forming a single-phase supersaturated solid solution of phase A.

[0013] Compared with the prior art, the present invention has the following advantages: 1. The method proposed in this invention has a fundamental advantage over traditional approaches that rely solely on mixing enthalpy, atomic scattering factor, or equivalent temperature, which are limited to specific systems and are mostly ex post facto interpretations. Its core advantage lies in the fact that this method introduces the principle of entropy increase from the thermodynamics of irreversible processes into the study of supersaturated solid solutions for the first time, constructing a clear physical picture and a clear evolutionary path. The core driving force of this model—the dominant driving force of entropy generation under strain on the mixing process—is directly rooted in the basic principles of thermodynamics, thus overcoming the predicament of traditional theories lacking a unified framework.

[0014] 2. As an a priori predictive analysis method, the mixing entropy model of this invention can not only reveal the inherent law that each phase will inevitably evolve towards a high-entropy state along the mixing entropy curve under the drive of severe plastic deformation (SPD), but also achieve quantitative prediction that traditional methods cannot reach: it can prospectively determine the direction of compositional evolution of each phase and accurately determine the crystal structure of the final single-phase solid solution. This unified and self-consistent theoretical framework has successfully solved the long-standing problem of "why different mechanisms contradict each other in different systems", and has elevated the study of SPD-induced supersaturated solid solutions from scattered phenomenon descriptions to the predictive science level based on basic principles.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is the mixing entropy-composition relationship diagram of the target AB binary alloy in this invention.

[0017] Figure 2 This is a schematic diagram of the mixed entropy analysis model of the Cu-5at%Ag binary alloy in Example 1 of the present invention.

[0018] Figure 3 This is a strain gradient microstructure diagram formed on the surface of the Cu-5at%Ag binary alloy after SPD in Example 1 of the present invention. Detailed Implementation

[0019] Figure 1 This is the mixing entropy-composition relationship diagram of the target AB binary alloy in this invention, from... Figure 1 As can be seen from this, the present invention is based on Using the X-axis as the reference, Plot a mixing entropy-composition relationship diagram with the Y-axis as the axis. Mark the average composition line of the target AB binary alloy on the diagram. For the AB binary alloy in the initial equilibrium state, the composition points of the A phase and the B phase are located at opposite ends of the diagram. The B content in the A phase is extremely low, and the A content in the B phase is also extremely low. This causes the mixing entropy of both the A phase and the B phase to approach zero. When SPD is applied to the target AB binary alloy, the composition of both the A phase and the B phase evolves along the mixing entropy curve in the direction of increasing mixing entropy. Specifically, the concentration of B atoms in the A phase gradually increases, and the concentration of A atoms in the B phase also gradually increases. When the A phase reaches the average composition of the alloy, according to the lever law, the B phase completely dissolves, and the system evolves into a single-phase supersaturated solid solution of A.

[0020] Example 1 This embodiment includes the following steps: Step 1: For the Cu-5at%Ag binary alloy, use the mixing entropy formula Calculate and plot the concentration of Ag component The horizontal axis represents the mixed entropy. The vertical axis represents the mixing entropy-composition relationship plot, see [link / reference]. Figure 2 ; Step 2: On the mixing entropy-composition relationship diagram drawn in Step 1, mark the average composition line of the Cu-5at%Ag binary alloy, i.e., Ag at% is 5at%, and the composition points corresponding to the Cu and Ag phases in the initial equilibrium state. For the Cu-5at%Ag binary alloy in the initial equilibrium state, the compositions of the Cu and Ag phases are located at opposite ends of the diagram. The Ag content in the Cu phase is extremely low, and the Cu content in the Ag phase is also extremely low. This causes the mixing entropy of both the Cu and Ag phases to approach zero. The calibrated mixing entropy-composition relationship diagram is obtained. (See...) Figure 2 The initial composition point of the Cu phase is the point where the at% of Ag in the figure is 0%, and the initial composition point of the Ag phase is the point where the at% of Ag in the figure is 100%. Step 3: Based on the principle of non-equilibrium thermodynamics, the intense plastic deformation process is defined as the continuous external entropy generation source of the target alloy, and it is determined that this entropy generation source provides the driving force for the mixing process. The driving force originates from the entropy generation caused by external mechanical deformation during the intense plastic deformation process. This driving force dominates the dynamic competition between element mixing and element demixing, and makes the element mixing process dominant. Step 4: On the calibrated mixing entropy-composition relationship diagram obtained in Step 2, based on the driving force described in Step 3, describe and predict the composition evolution of the two phases of the target Cu-Ag binary alloy under the action of severe plastic deformation: When SPD is applied to the Cu-5at%Ag binary alloy, the composition of both Cu and Ag phases evolves along the mixing entropy curve in the direction of increasing mixing entropy. Specifically, the concentration of Ag atoms in the Cu phase gradually increases, and the concentration of Cu atoms in the Ag phase also gradually increases. When the composition of the Cu phase reaches the average composition of the alloy, according to the lever law, the Ag phase completely dissolves, and the system eventually evolves into a Cu single-phase supersaturated solid solution.

[0021] The strain-induced supersaturated solid solution analysis method for the immiscible alloy system based on mixed entropy evolution in this embodiment was experimentally verified: A surface SPD was performed on a Cu-5at%Ag binary alloy, see [link to relevant documentation]. Figure 3 This treatment creates a gradient strain along the depth direction of the alloy, meaning the strain increases significantly with decreasing distance from the surface, leading to changes in the composition of the Cu and Ag phases. TEM energy dispersive spectroscopy analysis was performed on the phases and their composition at four depths: 2000 μm, 400 μm, 200 μm, and 10 μm. The data in Table 1 shows that as the depth decreases (i.e., strain increases), the evolution of Ag content in the Cu phase is: 0 → 1 at% → 3 at% → 5 at% (at which point the Cu composition reaches the average alloy composition), and the evolution of Cu content in the Ag phase is: 0 → 10 at% → 40 at%. Ultimately, a single-phase supersaturated Cu solid solution forms at the surface with the highest strain. This result is completely consistent with the model prediction that the Ag atom concentration in the Cu phase gradually increases, the Cu atom concentration in the Ag phase also gradually increases, and the system eventually evolves into a single-phase supersaturated Cu solid solution. This strongly confirms the reliability of the present invention.

[0022] Table 1

[0023] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution, characterized in that, The method includes the following steps: Step 1: For the target AB binary alloy, calculate and plot the mixing entropy-composition relationship graph with the concentration of component B as the horizontal axis and the mixing entropy as the vertical axis using the mixing entropy formula; Step 2: On the mixing entropy-composition relationship diagram drawn in Step 1, mark the average composition line of the target AB binary alloy, as well as the composition points corresponding to phase A and phase B under the initial equilibrium state, to obtain the calibrated mixing entropy-composition relationship diagram; Step 3: Based on the principle of non-equilibrium thermodynamics, the intense plastic deformation process is defined as a continuous external entropy generation source of the target alloy, and it is determined that this entropy generation source provides a driving force for the mixing process, promoting the continuous increase of the mixing degree. Step 4: On the calibrated mixing entropy-composition relationship diagram obtained in Step 2, based on the effect of the driving force in Step 3 on promoting the increase of mixing degree, describe and predict the composition evolution of the two phases of the target AB binary alloy under severe plastic deformation: that is, the composition of phase A and phase B evolves in the direction of increasing mixing entropy until one phase dissolves and finally forms a single-phase supersaturated solid solution.

2. The strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution according to claim 1, characterized in that, The formula for the mixed entropy mentioned in step one is: ,in, S The entropy of mixing for a single phase, and These represent the atomic percentages of atoms A and B in this phase, respectively. The gas constant is 8.314 J / (mol·K).

3. The strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution according to claim 1, characterized in that, In step two, the atomic percentage of component B in the average composition of the alloy is no greater than 50%.

4. The strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution according to claim 1, characterized in that, The driving force mentioned in step three originates from the entropy generated by external mechanical deformation during intense plastic deformation. This driving force dominates the dynamic competition between element mixing and element demixing, and gives the element mixing process an advantage.

5. The strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution according to claim 1, characterized in that, The specific path of component evolution described in step four is as follows: the concentration of B atoms in phase A increases synchronously with the concentration of A atoms in phase B.

6. The strain-induced supersaturated solid solution analysis method for immiscible alloy systems based on mixed entropy evolution according to claim 1, characterized in that, The determination of the evolution endpoint state in step four is based on the following: when the composition of phase A reaches the average composition of the alloy, according to the lever law, phase B completely dissolves, forming a single-phase supersaturated solid solution of phase A.

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