Study On The Plastic Deformation Of Single-Crystal Nanoscale Titanium With Molecular Dynamics Method

The metal titanium which is one of the most important structural materials in 21st century has been widely used in various fields owing to its excellent performance such as high strength,low density and superior corrosion resistance.The plastic deformation mechanism of titanium has been a focus for researchers.With the development of nanotechnology,it is found that the mechanical behavior of metallic materials with dimensions down to the nanometer scale is very different from that of corresponding bulk materials.It is of great significance to understand the mechanical properties and deformation mechanisms of materials at the nanometer scale from the microscopic point of view,which is investigated with the molecular dynamics simulation method in this paper.When titanium single crystal nano-pillars are uniaxially compressed along the[0001]at 300K and 1×10⁸s^-1,pyramidal partial dislocations are preferentially nucleated on the surface of common boundary between the fixed layer and the zone which can be moved since the stress concentrates at the edges of the nano-pillars.Then the<c+a>pyramidal slip system are activated and its Burgers vector is 1/3[1213],which effectively coordinates the horizontal and vertical deformation,and there are stacking fault in the part of model,forming some fee structure to reduce the overall stress.Additionally,no twinning is found and the plastic deformation is dominated by the pyramidal dislocation movement during the entire deformation process,which is related to the size effect of the deformation twin.The plastic deformation mode of prism nano-pillars is consistent with that of cylinder nano-pillars,however,both the yield stress and the stress local maximum of prism nano-pillars are smaller than that of cylinder nano-pillars.When titanium single crystal nano-pillars are uniaxially tensed along the[0001]at 300K and 1×10⁸s^-1,the {1012} twin preferentially nucleates at the interface between the（1100）surface and the（1120）surface to dominate the plastic deformation,followed by the necking in the secondary twinning zone,and then the crack that crosses the midsection of the sample is formed by hole,indicating that macroscopic fracture has taken place.Besides the conventional {1012} plane,semi-coherent basal-prismatic interfaces between parent and reoriented crystal are also observed under tensile loading.While at 450K,1x10⁸s^-1 and 300K,5x10⁸s^-1,there are two twin embryo that indicate the number of equivalent surface nucleation sites increases with the temperature and strain rate.The yield stress of the nano-pillars under tension is much larger than that under compression,that is mainly caused by the different initial deformation mechanisms under the two loading conditions.The compressive flow stress of the nano-pillars is also larger than the tensile flow stress,since the new c-axis direction and the loading direction are no longer parallel to each other in the reoriented crystal after the twin deformation,making base slip to be actived during the tensile deformation.