Investigation on tensile properties of nanocrystalline titanium with ultra-small grain size

Molecular dynamics was used to simulate tensile behavior of nanocrystalline titanium with ultra-small grain size ranging from 2.8 nm to 10.2 nm at the strain rate ranging from 10(8) s(-1) to 10(10) s(-1). Three dimensional samples with random oriented grains containing no textures were developed by Voronoi tessellation. For all the samples, the yielding is solely controlled by GB mediated process. The inverse Hall-Petch relation between grain size and flow stress was found. The strain rate sensitivity shows increase with the decrease of grain size due to the enhancement of grain boundary (GB) mediated process. Meanwhile, it increases with the applied strain rate due to the local disorder around GBs. Remakeable grain coarsening observed in the 2.8 nm sample causes the slight increase of flow stress. Both GB mediated process and partial dislocation slips play an important role in the plastic deformation of nanocrystalline Ti. With the increase of grain size, rare twins initiated from GBs can be observed. From the size dependent dislocation density analysis, it is concluded that with the increase of grain size, dislocation related deformation contributes more to the plastic strain. (C) 2017 Elsevier B.V. All rights reserved.