A design method of nano-l12 phase precipitation strengthened fcc-based high-entropy alloy

Abstract

The application discloses a design method of a nano L12 phase precipitation strengthened FCC-based high-entropy alloy, and the method is characterized in that a method for predicting the formation of a matrix phase by calculating a thermophysical and chemical parameter alpha related to phase formation is combined with CALPHAD calculation to provide calculation assistance for designing the precipitation strengthened high-entropy alloy. The method comprises the following steps: defining suitable elements for forming a matrix phase and a precipitated phase from a thermodynamic database according to the influence of different elements on phase formation; selecting 136 alloys with different component types, and dividing the 136 alloys into single-phase FCC, single-phase BCC, FCC+BCC and SS+IM; combining four parameter combinations of |ΔH mix |, ΔS mix , T melt , VEC with atomic size difference to predict the formation of the FCC phase, obtaining the parameter range of the FCC matrix phase formation, and adjusting the suitable element ratio according to the parameter range; and adding L12 phase forming elements such as Al, Ti and Cu to introduce a second phase by using the 'addition' principle of alloy design, and optimizing the content of the added alloy elements by means of CALPHAD calculation combined with experiments. Finally, the FCC-based high-entropy alloy with high density nano L12 phase precipitation strengthening is prepared.

Description

Technical Field

[0001] The invention belongs to the technical field of high entropy alloys, and in particular relates to a design method for a nano L12 phase precipitation-strengthened FCC-based high entropy alloy. Background Art

[0002] Traditional alloy design is mainly based on forming alloys with a main element and multiple other elements in small additions to obtain the desired properties, such as corrosion resistance, toughness, strength, ductility, and thermal properties. However, this strategy restricts alloy design to the corners of the phase diagram, leaving the central region of the vast multi-component phase space unexplored. In 2004, a new strategy proposed by Yeh, Cantor and others changed the traditional alloy design paradigm and included equiatomic or near-equiatomic mixtures of multiple main alloying elements, thus giving rise to the concept of high entropy alloys (HEA) or multi-principal element alloys.

[0003] For such a complex multi-component system, simply looking at the types of second phases, a wide variety of structural second phases (such as L12, L21, and B2 ordered phases, as well as σ and η phases) can be stably present in a high-entropy alloy matrix through alloying and heat treatment. However, experimentally studying the stability, composition, and relationships of second phase precipitation in multi-component systems is both labor-intensive and inefficient. Summary of the Invention

[0004] Phase diagram thermodynamics can easily address these issues. Using phase diagrams not only aids in the compositional design of precipitation-strengthened high-entropy alloys and the development of novel alloy compositions, but also effectively helps determine heat treatment temperatures to obtain different second-phase particles and even control the size and morphology of the second phase. Therefore, CALPHAD is a new and effective research method for the design of second-phase-strengthened high-entropy alloys.

[0005] In recent years, the parameter calculation method for predicting the formation of alloy phases has received increasing attention. Scholars have proposed parameters including mixing enthalpy, mixing entropy, atomic radius difference, electronegativity difference, and valence electron number to predict the formation rules of solid solution phase, topological close-packed phase, and amorphous phase in high entropy alloys, and summarized the relationship between the value range of each parameter and the phase composition of the high entropy alloy system. The development of parameter calculation method has greatly promoted the design of high entropy alloys. The parameter conditions for the formation of solid solution phase in high entropy alloys are the most important research direction for predicting the formation rules of alloy phases in parameter calculation method. It is generally believed that there are three major principles for the formation of solid solution phase in multi-principal element high entropy alloys: ① contain at least 5 main elements; ② the maximum atomic radius difference between elements is less than 12%; ③ the alloy mixing enthalpy is between -40-10kJ / mol. In order to obtain more accurate phase formation rules, Zhang Yong et al. comprehensively considered the effects of entropy and enthalpy on the formation of high entropy alloy phases and proposed a new parameter Ω to replace ΔH mix ΔH in the -δ criterion mix When the driving force for solid solution phase formation is T·ΔS mix Greater than resistance ΔH mix That is, when Ω > 1, the alloy tends to form a solid solution phase. Conversely, when Ω < 1, the alloy is more likely to form complex phases such as intermetallic compounds. Furthermore, the valence electron concentration is also believed to be closely related to phase formation. Research has shown that when the valence electron number is ≥ 8, the alloy tends to form a face-centered cubic solid solution phase; when the valence electron number is ≤ 6.87, the alloy tends to form a body-centered cubic solid solution phase; and when the valence electron number is between these two, a mixed solid solution phase of face-centered cubic and body-centered cubic forms is formed. Tian et al. proposed that high-entropy alloys with a valence electron number in the range of 7.80-9.50 tend to form a face-centered cubic structure, while alloys with a valence electron number in the range of 4.33-7.55 tend to form a body-centered cubic structure. Tsai et al. found that the formation of σ phase is directly related to the valence electron content of the alloy: for alloys containing V or Cr, when the valence electron content is between 6.88 and 7.84, the alloy will form σ phase in the as-cast state or after suitable annealing. Therefore, current work has not yet achieved accurate differentiation of the various phases, and calculation of the physicochemical parameters of multicomponent alloys remains difficult. In 2006, scholar Ouyang Yifang combined the geometric model with the Miedema model to predict the mixing enthalpy of quaternary amorphous materials, finding that the GSM model's predictions agreed well with experimental values.

[0006] Therefore, the present invention uses a method of extrapolating relevant parameters based on binary alloy data using geometric models to obtain more accurate multi-component alloy physicochemical parameters, thereby optimizing the prediction parameters that can distinguish different solid solution phases. In this invention, a total of 136 alloys with different numbers of component types were selected and divided into four categories: single-phase FCC, single-phase BCC, FCC+BCC, and SS+IM. Using |ΔH mix |,ΔSmix 、T melt The four parameter combinations of VEC and atomic size difference are combined to predict the formation of the FCC phase, and the parameter range for the formation of the FCC matrix phase is obtained, and the appropriate element ratio is adjusted accordingly. Then, the "additive" principle of alloy design is adopted to introduce the second phase by adding L12 phase-forming elements such as Al, Ti, and Cu. The content of the added alloying elements is optimized through CALPHAD calculations combined with experiments. Ultimately, it is expected to prepare FCC-based high-entropy alloys with high-density nano-L12 phase precipitation strengthening, providing a paradigm for accelerating the design of high-entropy alloy composition and phase structure.

[0007] The purpose of this invention is to provide a design method for nano-L12 phase precipitation-strengthened FCC-based high entropy alloys. This method uses a method based on binary alloy data to extrapolate relevant parameters using a geometric model to obtain relatively accurate multi-component alloy physicochemical parameters, thereby optimizing the prediction parameters that can distinguish different solid solution phases. mix |,ΔS mix 、T melt The four parameter combinations of α, α, and β (VEC) combined with atomic size differences predict the formation of the FCC phase, deriving the parameter range for FCC matrix phase formation and adjusting the appropriate element ratio accordingly. Subsequently, the "additive" principle of alloy design was employed to introduce a secondary phase by adding L12 phase-forming elements such as Al, Ti, and Cu. The content of these added alloying elements was optimized through CALPHAD calculations combined with experiments. Ultimately, an FCC-based high-entropy alloy with a high-density nano-L12 phase precipitation strengthening was produced.

[0008] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0009] (1) Based on the influence of different elements on phase formation, the appropriate elements for the matrix phase and precipitation phase are defined from the thermodynamic database;

[0010] (2) Through the analysis and calculation of 136 alloys with different types and numbers of components, the |ΔH mix |,ΔS mix 、T melt 、VEC these four parameters are designed through certain combination The formation of FCC phase is predicted by combining the atomic size difference, the parameter range of FCC matrix phase formation is obtained, and the appropriate element ratio is adjusted accordingly;

[0011] (3) The FCC matrix alloy obtained in step (2) is then alloyed with L12 phase-forming elements such as Al, Ti, and Cu. The equilibrium phase diagram of the overall alloy is calculated by CALPHAD thermodynamics to optimize the ratio of the alloying elements so that the alloy tends to form an FCC+L12 two-phase structure;

[0012] (4) Verify the alloy phase result in step (3) through experiments. If it is not satisfied, return to step (1).

[0013] The added content of the FCC matrix phase forming elements in steps (2) and (3) is 70%-80% (at.%); the added content of the L12 phase forming elements is 20%-30% (at.%). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The corresponding relationship between the thermodynamic parameters α-δ and the matrix phase calculated by the present invention is shown in the figure. mix |,ΔS mix 、T melt The four parameters of , VEC are designed through certain combinations. The combination combines the atomic size difference to predict the formation of the FCC phase, and the parameter range for the formation of the FCC matrix phase is shown in the blue area;

[0015] Figure 2 This is the equilibrium phase diagram of the (FeCoNi)81.7Al6.65Ti6.65Cu5 alloy near the service temperature according to an embodiment of the present invention;

[0016] Figure 3 This is a microstructure image of the (FeCoNi)81.7Al6.65Ti6.65Cu5 alloy under a scanning electron microscope according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and examples so that those skilled in the art can implement the invention with reference to the description. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0018] Example: (FeCoNi)81.7Al6.65Ti6.65Cu5 alloy

[0019] (1) Based on the influence of different elements on phase formation, the elements Fe, Co, and Ni that constitute the matrix phase and the elements Al, Ti, and Cu that constitute the precipitation phase are defined from the thermodynamic database;

[0020] (2) Based on the data of Fe-Co, Fe-Ni, and Co-Ni binary alloys, the mixing enthalpy ΔH of Fe-Co-Ni ternary alloy is extrapolated using the GSM model. mix ;ΔS mix According to the definition of entropy by Boltzman's law, the formula calculated; Therefore, the calculated parameters of the alloy of Fe:Co:Ni=1:1:1 are α=11.46 and ε=0.38, which fall within the range of FCC single-phase formation, as shown in Figure 1 The position of the pentagram is shown in the figure;

[0021] (3) The FCC matrix alloy obtained in step (2) is then alloyed with L12 phase-forming elements such as Al, Ti, and Cu. The equilibrium phase diagram of the overall alloy is calculated using Pandat software and the PanHEA database, and the ratio of the alloying elements is optimized so that the alloy tends to form an FCC+L12 two-phase structure. The embodiment (FeCoNi)81.7Al6.65Ti6.65Cu5 alloy falls within the two-phase phase diagram range.

[0022] (4) The phase diagram calculation results of step (3) were experimentally verified by X-ray diffraction analysis (Discover-8) and scanning electron microscopy analysis (Sigma300). Figure 3 As shown in the figure, the alloy consists of a two-phase structure of FCC+L12 and has a high density of nano-L12 phase precipitation.

Claims

1. A design method for nano-L12 phase precipitation-strengthened FCC-based high entropy alloy, characterized by: The method comprises the following steps: (1) Based on the influence of different elements on phase formation, the appropriate elements for the matrix phase and precipitation phase are defined from the thermodynamic database; (2) Through the analysis and calculation of 136 alloys with different types and quantities of components, the 、 、 、 These four parameters are combined to design parameter α, which is combined with the atomic size difference to predict the formation of FCC phase, and the parameter range of FCC matrix phase formation is obtained, and the appropriate element ratio is adjusted accordingly; (3) The FCC matrix alloy obtained in step (2) is then alloyed with L12 phase-forming elements such as Al, Ti, and Cu. The equilibrium phase diagram of the overall alloy is calculated by CALPHAD thermodynamics to optimize the ratio of the alloying elements so that the alloy tends to form an FCC+L12 two-phase structure. (4) Verify the alloy phase result in step (3) through experiments. If it is not satisfied, return to step (1); The parameter α in step (2) is expressed as follows: ; The FCC matrix forming elements in step (1) are the following 3d transition group elements: Fe, Co, Ni, Mn, Cr; the L12 phase forming elements are: Al, Ti, Nb, Ta, Cu.

2. The design method of a nano-L12 phase precipitation-strengthened FCC-based high entropy alloy according to claim 1, characterized in that: Described in step (2) 、 、 、 The combination of the four parameters is obtained through the following analysis: The more negative the calculated value is, the better the bonding between elements is, and the tendency is to form intermetallic compounds; The more positive the calculated value is, the easier it is for the element to segregate and have low miscibility in liquid state. The larger it is, the more difficult it is to form a solid solution phase, so this item is regarded as the resistance to the formation of the FCC matrix; Indicates the valence electron concentration of an element. According to the Hume-Rothery law, the higher the number of valence electrons, the lower the solubility of the element. Therefore, this term is regarded as the resistance to the formation of the FCC matrix. The greater the alloy mixing entropy, the smaller the free energy, and the easier it is to form a solid solution. This term is considered to be the driving force for FCC matrix formation.

3. The design method of a nano-L12 phase precipitation-strengthened FCC-based high entropy alloy according to claim 1, characterized in that: The added content of the FCC matrix phase forming elements is 70-80 at.%; the added content of the L12 phase forming elements is 20-30 at.%.

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