冲击加载下铝中氦泡和孔洞的塑性变形特征研究

Plastic deformation of helium bubble and void in aluminum under shock loading

通过分子动力学模拟研究了在相同冲击加载强度下单晶铝中氦泡和孔洞的塑性变形特征,结果发现氦泡和孔洞的塌缩是由发射剪切型位错环引起的,而没有观测到棱锥型位错环发射.氦泡和孔洞周围的位错优先成核位置基本一致,但是氦泡周围发射的位错环数目比孔洞多,位错环发射速度明显比孔洞快.且氦泡和孔洞被冲击波先扫过部分比后扫过部分发射位错困难.通过滑移面上的分解应力分析发现,氦泡和孔洞周围塑性特征的差别是由于氦泡内压引起最大分解应力分布改变造成的.氦泡和孔洞被冲击波先后扫过部分塑性不对称是因为冲击波扫过时引起形状变化,使这两部分位错临界成核应力阈值不同造成的.研究结果有助于深入认识辐照损伤对金属材料动态性能影响的微观机理.

The characteristic of microscopic plasticity associated with collapse of helium bubble and void in single-crystal aluminum under the same shock loading strength has been investigated by molecular dynamics （MD） simulations. The results show that both the helium bubble and the void collapse through the emission of shear dislocation loops, while prismatic dislocation loops are never observed in the simulations. The preferential dislocation nucleation sites are similar for the helium bubbles and the voids, but the number of dislocations emitted from the helium bubble outnumbers that from the voids, and the dislocation loops emitted from the helium bubbles move faster than that from the voids. Meanwhile, it is more difficult to emit dislocation loops from the leading side （the side which the shock hits first） of both the helium bubbles and the voids than from the trailing side. By analysing the resolved shear stress along the slip plane, we found that the internal pressure of the helium bubbles increase the resolved shear stress and make the dislocation emission from the helium bubbles much easier than from the voids. The curvature change from the leading side to the trailing side produced by the shock modifies the critical shear stress for dislocation nucleation, which explains the difference in the plasticity between the leading side and the tailing side of both the helium bubbles and the voids. The result will contribute to a better understanding of the microscopic mechanism through which irradiation damages affect the dynamic properties of metals.