晶粒尺寸和孪晶界间距对纳米多晶铝合金塑性变形影响的分子动力学模拟研究

采用分子动力学模拟方法，分别研究了晶粒尺寸和孪晶密度对纳米多晶铝合金塑性变形的影响。模拟结果表明，弛豫后的位错密度对纳米多晶Al的微观结构演变和逆Hall-Petch关系产生了重要影响。变形受晶粒大小限制，在细晶中可形成层错四面体和复杂层错结构，从而激活了晶界的辅助变形。当孪晶界间距（TBS）较大时，Shockley分位错在晶界处形核并增殖。然而，随着TBS的减小，孪晶界成为Shockley分位错的来源。孪晶界上大量的分位错形核会导致孪晶界迁移甚至消失。在塑性变形过程中还观察到形变纳米孪晶。研究结果为开发具有可调节力学性能的先进纳米多晶Al提供了理论基础。

Effect of Grain Size and Twin Boundary Spacing on Plastic Deformation of Nano-polycrystalline Al Alloy by Molecular Dynamics Study

The molecular dynamics simulations were used to study the effect of grain size and twin density on the plastic deformation of nano-polycrystalline aluminum alloy. The results show that the dislocation density after relaxation is crucial to the microstructure evolution and the inverse Hall-Petch relation of the nano-polycrystalline Al. The staggered tetrahedrons and complex staggered structures are formed in the fine grains, which is attributed to the restriction of grain size. Thus, the auxiliary deformation of grain boundary is activated. The Shockley partial dislocations nucleate and multiply at the grain boundaries when the twin boundary spacing (TBS) is relatively large. However, with decreasing the TBS, the twin boundary becomes the source of the Shockley partial dislocations. A large number of partial dislocation nucleations at the twin boundary will cause the twin boundary to migrate or even disappear. The deformed nano-twins can also be observed during the plastic deformation process. This research provides theoretical basis for the development of advanced nano-polycrystalline Al alloy with adjustable mechanical properties.