合金的力學性能在微觀尺度上與電子和原子行為有關; 然而,原子鍵合的強度並不直接關聯材料宏觀的力學性能,如屈服強度、斷裂韌性和耐疲勞性等。這是因為介觀尺度的微觀結構包括各種缺陷,如雜質、晶界和位錯,它們干預或增強了合金對外力的響應,引起非線性和多尺度現象。來自日本東北大學的Tetsuo Mohri及其同事,結合電子結構計算和統計力學手段,對富Fe硅合金力學性能的物理起源問題作了綜述。用電子結構計算研究彈性性能,可將Si含量增加時延展性損失的物理起源,歸因於磁體積和D03有序的組合效應。以形成微結構的異質性為例,用高精度電子結構計算研究Si原子的偏析行為,可以找到兩種分離位點,即鬆散位點和緊密位點,其分離機制因場所而異。通過電子結構計算,結合分子動力學模擬,對固溶硬化和軟化作了解釋。此外,他們還基於動力學蒙特卡羅模擬,討論了特定加工硬化行為的線索。該文近期發表於npj Computational Materials 3:10 (2017),標題與摘要如下。點擊閱讀原文,可以自由下載論文PDF。


Mechanical properties of Fe-rich Si alloy from Hamiltonian (用哈密爾頓計算揭示富Fe硅合金的力學性能)

Testsuo Mohri, Ying Chen, Masanori Kohyama, Shigenobu Ogata, Arkapol Saengdeejing, Somesh Kumar Bhattacharya, Masato Wakeda, Shuhei Shinzato & Hajime Kimizuka

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.


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