CALPHAD-aided design of high entropy alloy to achieve high strength via precipitate strengthening

CALPHAD辅助设计高强度沉淀强化型高熵合金（英文）

Designing high entropy alloys(HEAs) with high strength and excellent ductility has attracted extensive scientific interest. In the present work, the CALPHAD(calculation of phase diagrams) method was applied to guide the design of an(FeCoNi)92Al2.5Ti5.5 HEA strengthened by precipitation hardening. The grain size as well as the size and volume fraction of the precipitates was tailored via a thermomechanical process to optimize the mechanical properties.The uniformly dispersed nano-precipitates are Ni3(Al,Ti)-type precipitates with an L12 ordered structure presenting a fully coherent interface with the face-centered cubic(FCC) matrix.The yield strength of the alloy increases from 338.3 to1355.9 MPa and the ultimate tensile strength increases from 759.3 to 1488.1 MPa, while the elongation maintains a reasonable value of 8.1%. The striking enhancement of strength is mainly caused by the precipitate’s hardening mechanism,which is evaluated quantitatively by various analytical models.The deformation-induced microbands and the coherent precipitates sheared by dislocations are the deformation and strengthening mechanisms contributing to the superior combination of ductility and strength in the present HEA.This investigation demonstrates that the CALPHAD method is beneficial to the design and optimization of HEAs.

近年来,设计具有高强度和优异延展性的高熵合金(HEAs)引起了人们的广泛兴趣.在本文中,我们采用CALPHAD方法来设计沉淀强化型(FeCoNi)92Al2.5Ti5.5高熵合金.通过热机械处理过程来调控合金晶粒尺寸、析出相大小及体积分数,从而优化合金力学性能.在一定温度时效后,具有L12有序结构的Ni3(Al,Ti)型第二相在面心立方(FCC)基体中均匀析出,并与FCC基体共格.通过热机械处理过程,合金的屈服强度从338.3 MPa增加到1355.9 MPa,抗拉强度从759.3 MPa增加到1488.1 MPa,而伸长率仍然保持在8.1%.基于分析模型定量评估屈服强度的增加,结果表明屈服强度的显著增加主要是由沉淀强化机制引起的.变形引起的微观条带和位错切过析出相是该合金的变形机制和强化机制,有助于该合金同时具有优异的延展性和高强度.本研究表明, CALPHAD方法可以为高熵合金的设计和优化提供借鉴.