动态压缩下马氏体相变力学性质的微观研究

Atomistic simulation of mechanical properties of martensitic transformation under dynamic compression

使用分子动力学方法,模拟了活塞以恒定加速运动从一端压缩单晶铁(沿[001]晶向)发生马氏体相变的微观过程.根据模拟结果将上述压缩过程分为弹性压缩、晶格软化、相变(bcc至hcp)、超应力松弛和高压相弹性压缩五个阶段,对各阶段的原子滑移规律和应力变化特征做了详细分析.分析得出应力超过约10GPa时,开始出现弹性常数软化行为;层错结构(fcc)和孪晶界为新相形核的两种缺陷,前者更为稳定;相变后粒子首先进入超应力松弛状态(即沿加载方向的偏应力呈现负值),在应力超过约36GPa粒子转变为高压相弹性压缩状态.

Molecular dynamics simulation （MD） was used to investigate the microscopic mechanism of martensitic transformations in Fe single crystals driven （along [001] orientation） by an accelerating piston. Simulated results revealed that the above compression process can be divided into five stages,namely the elastic compression,softening of elastic ratio,phase transformation （bcc to hcp）,over-relaxation of stress and elastic compression of high-pressure phase. The slipping laws of atoms and properties of stress are analysed in detail. Atoms can only slip along longitudinal direction under elastic compression,and when the longitudinal stress is beyond 10 GPa,local atoms begin to slip along lateral direction and form embryos,which is just the microscopic nature of the softening of elastic ratio.The stacking fault （fcc） is a more steady origin of crystal nucleation than the twin boundary. After the phase transformation,the atoms undergo an over-relaxation of stress （i.e.,the lateral stress is larger than the longitudinal stress）,and this state disappears when the longitudinal stress is beyond about 36 GPa.