纳米多晶铁的冲击相变研究

利用分子动力学方法研究了不同晶粒度的纳米多晶铁在冲击压缩下的结构相变过程,模拟结果表明:纳米多晶铁的冲击结构相变(由体心立方(bcc)结构 α 相到六角密排(hcp)结构 ε 相)发生的临界冲击应力在15 GPa左右.纳米多晶铁在经过弹性压缩变形后,晶界导致的塑性变形开始发生,然后大多数相变从晶界成核并最终发展为大规模相变.不同变形过程在应力和粒子速度剖面上能得到清晰的体现,并通过微观原子结构分析分辨.冲击压缩后的微观结构以晶界原子和以fcc结构原子充当孪晶界的hcp原子为主.晶粒度明显影响晶界变形及相变 关键词： 冲击相变 纳米多晶铁 冲击波 分子动力学

Shock-induced phase transformation in nanocrystalline iron

The shock-induced phase transformation of nanocrystalline iron with different grain sizes is investigated by using molecular dynamic simulations. The critical shock stress for shock-induced phase transformation (from body-cubic centered α phase into hexagonal-close packed ε phase) of nanocrystalline irons is about 15 GPa. Under shock compression, the nanocrystalline irons first experience elastic deformation, then plastic deformation purely caused by grain boundaries, after that phase transformation nucleated mostly at the grain boundaries, and finally nucleation areas expanding into the entire samples. These processes can be reflected by the stress profile and the particle velocity profile, and also be distinguished by local atomic structures analyses in the corresponding areas. The microstructures of the shocked samples consist of grain boundary and hexagonal-closed packed new phase with the face-cubic centered atoms as the twin boundary. The grain size obviously influences the deformation of grain boundary and the microstructure after shock compression, and turns to change the profiles of stress or velocity. The mechanism is primarily analyzed.