富铁硅合金机械性能的内在物理机制

合金的力学性能在微观尺度上与电子和原子行为有关; 然而，原子键合的强度并不直接关联材料宏观的力学性能，如屈服强度、断裂韧性和耐疲劳性等。这是因为介观尺度的微观结构包括各种缺陷，如杂质、晶界和位错，它们干预或增强了合金对外力的响应，引起非线性和多尺度现象。来自日本东北大学的Tetsuo Mohri及其同事，结合电子结构计算和统计力学手段，对富Fe硅合金力学性能的物理起源问题作了综述。用电子结构计算研究弹性性能，可将Si含量增加时延展性损失的物理起源，归因于磁体积和D03有序的组合效应。以形成微结构的异质性为例，用高精度电子结构计算研究Si原子的偏析行为，可以找到两种分离位点，即松散位点和紧密位点，其分离机制因场所而异。通过电子结构计算，结合分子动力学模拟，对固溶硬化和软化作了解释。此外，他们还基于动力学蒙特卡罗模拟，讨论了特定加工硬化行为的线索。该文近期发表于npj Computational Materials 3:10 (2017)，标题与摘要如下。点击阅读原文，可以自由下载论文PDF。

The physical origins of the mechanical properties of Fe-rich Si alloys are investigated by combining electronic structure calculations with statistical mechanics means such as the cluster variation method, molecular dynamics simulation, etc, applied to homogeneous and heterogeneous systems. Firstly, we examined the elastic properties based on electronic structure calculations in a homogeneous system and attributed the physical origin of the loss of ductility with increasing Si content to the combined effects of magneto-volume and D03 ordering. As a typical example of a heterogeneity forming a microstructure, we focus on grain boundaries, and segregation behavior of Si atoms is studied through high-precision electronic structure calculations. Two kinds of segregation sites are identified: looser and tighter sites. Depending on the site, different segregation mechanisms are revealed. Finally, the dislocation behavior in the Fe–Si alloy is investigated mainly by molecular dynamics simulations combined with electronic structure calculations. The solid-solution hardening and softening are interpreted in terms of two kinds of energy barriers for kink nucleation and migration on a screw dislocation line. Furthermore, the clue to the peculiar work hardening behavior is discussed based on kinetic Monte Carlo simulations by focusing on the preferential selection of slip planes triggered by kink nucleation.