冲击波压缩下含纳米孔洞单晶铁的结构相变研究

利用分子动力学模拟方法对含纳米孔洞的单晶铁在冲击波压缩下的结构相变(由体心立方结构α到六角密排结构ε)进行了研究,单晶铁样品的尺寸为17.2nm×17.2nm×17.2nm，总原子数428341个，在样品的中央预置一个直径为1.12nm的孔洞，利用一活塞分别以350，500，1087m/s的速度撞击样品产生冲击波，对应的冲击波压缩应力分别为12，17，35GPa.撞击方向沿单晶铁的［100］晶向.计算结果表明，在冲击波压缩下，孔洞对铁中的相变起了诱导作用，伴随着孔洞的塌陷，相变首先出现在孔洞周围的(011)面和(011)面上，然后扩展到整个样品.通过分析冲击压缩下原子的位移历史，解释了相变的微观机制，发现孔洞周围的原子在{011}面上沿〈011〉晶向滑移，离孔洞中心距离越近的{011}面上的原子容易滑移，间隔一层的{011}面与相邻层原子的移动位移幅度不同，这种相对滑移导致出现了新的结构(hcp结构). 关键词： 相变 分子动力学 冲击波 纳米孔洞

Molecular dynamic simulation of shock-induced phase transformation in single crystal iron with nano-void inclusion

Shock-induced phase transformation (body-centered cubic α phase to hexagonal close-packed ε phase) in single crystal iron with a nano-void inclusion has been investigated by means of molecular dynamic (MD) simulation. The simulated sample is 17.2nm×17.2nm×17.2nm in size with 428341 atoms, and in the center of the sample settled a void of 1.12nm in diameter. The shock wave compression is generated by using a piston impact with the sample at velocities of 350m/s, 500m/s and 1087m/s, respectively. Shock wave propagates along the ［100］ direction in the sample. Results indicate that the existence of void is an important factor for inducing the phase transformation, which initially occurs around the void and mainly on the (011) and (011) planes, while with the increase of compression time it expands to the rest of the sample. By analyzing the moving history of atoms under shock wave compression, the phase transformation mechanism has been outlined. It is found that when the atoms at (011) planes slide to the void along ［011］ direction, they may have relatively different displacement, such that results in alternative positions compared to their initial location and yields the new structure (hcp).