梯度纳米结构多晶铝剪切变形的分子动力学模拟

Molecular dynamics simulation of shear deformation of gradient nanostructured polycrystalline aluminum

构筑4种不同梯度纳米结构的多晶铝原子结构模型,采用分子动力学方法对其进行结构弛豫与剪切变形的计算模拟,获得剪切形变过程中的位错演变和晶粒原子结构,研究在同一变形条件下不同梯度纳米结构多晶铝的晶粒形变机制和剪切变形过程中微观结构的变化,并研究其力学性能。结果表明,在剪切形变过程的初始及中间阶段,不同梯度纳米结构的形变机制基本一致,都发生大量位错运动并塞积在晶界处,而后穿过晶界,最终在晶粒表面释放。在变形过程的中后期,不同梯度纳米结构则表现不一样。其中剪切强度较大的结构,剪切形变后不存在贯穿多个晶粒的剪切带,且部分粗晶粒由于晶粒取向与剪切方向差异较大和晶粒旋转等原因分解为几个较小的晶粒,而细晶粒则无明显变化。剪切强度较小的结构在剪切形变过程中由于位错塞积与释放及晶界的相互连接而形成贯穿剪切带,严重影响剪切强度。

Gradient nanopolycrystalline structured metals are receiving increasing attention due to their unique plastic deformation mechanism and possible mechanical property enhancement.In this paper,the effect of different gradient nanostructures on the shear deformation behavior is investigated using a molecular dynamics approach.By comparing the dislocation evolution and atomic structure of grains during shear deformation of different gradient nanostructures,it is found that the deformation mechanisms of different gradient nanostructures are basically the same in the initial and intermediate stages of shear deformation process,with a large number of dislocations moving and accumulating at the grain boundaries,and then passing through the grain boundaries and finally releasing at the grain surface.In the middle and later stages of the deformation process,the different gradient nanostructures behave differently.For structures with higher shear strength,there is no shear band through multiple grains after shear deformation,and some of the coarse grains are broken into several smaller grains due to the large difference between grain orientation and shear direction and grain rotation,while the fine grains do not change significantly.The shear strength of the smaller structures is seriously affected by the shear bands formed during shear deformation due to dislocation plugging and release and interconnection of grain boundaries.