Grain boundary segregation and relaxation in nano-grained polycrystalline alloys

作     者：Tong-Yi Zhang Ying-Xin Gao Sheng Sun Tong-Yi Zhang;Ying-Xin Gao;Sheng Sun

作者机构：Materials Genome InstituteShanghai UniversityShanghai200444China 

出 版 物：《Science China(Physics,Mechanics & Astronomy)》 (中国科学：物理学、力学、天文学（英文版）)

年 卷 期：2021年第64卷第2期

页      面：72-90页

核心收录：

学科分类：07[理学] 08[工学] 070205[理学-凝聚态物理] 0805[工学-材料科学与工程（可授工学、理学学位）] 080502[工学-材料学] 0704[理学-天文学] 0702[理学-物理学] 

基　　金：supported by the National Key R&D Program of China(Grant No.2017YFB0701604) the National Natural Science Foundation of China(Grant No.11672168)for financial support。 

主　　题：nano-grained alloys thermal stability grain boundary segregation eigenstress eigenstrain 

摘      要：The present study carries out systematic thermodynamics analysis of Grain Boundary(GB)segregation and relaxation in NanoGrained(NG)polycrystalline alloys.GB segregation and relaxation is an internal process towards thermodynamic equilibrium,which occurs naturally in NG alloys without any applied loads,causes deformation and generates internal stresses.The analysis comprehensively investigates the multiple coupling effects among chemical concentrations and mechanical stresses in GBs and grains.A hybrid approach of eigenstress and eigenstrain is developed herein to solve the multiple coupling problem.The analysis results indicate that the GB stress and grain stress induced by GB segregation and relaxation can be extremely high in NG alloys,reaching the GPa level,which play an important role in the thermal stability of NG alloys,especially via the coupling terms between stress and concentration.The present theoretic analysis proposes a novel criterion of thermal stability for NG alloys,which is determined by the difference in molar free energy between a NG alloy and its reference single crystal with the same nominal chemical composition.If the difference at a temperature is negative or zero,the NG alloy is thermal stable at that temperature,otherwise unstable.