Modelling plastic deformation of nano/submicron-sized tungsten pillars under compression: A coarse-grained atomistic approach

http://dx.doi.org/10.1615/IntJMultCompEng.2018026027

Abstract

In this work, coarse-grained atomistic simulations via the concurrent atomistic-continuum (CAC) method are performed to investigate compressive deformation of nano/submicron-sized pillars in body-centered cubic (BCC) tungsten. Two models with different surface roughness are considered. All pillars have the same height-to-diameter aspect ratio of 3, with diameter ranging from 27.35 to 165.34 nm; as a result, the largest simulation cell contains 291,488 finite elements, compared with otherwise approximately 687.82 million atoms in an equivalent full atomistic model. Results show that (i) a larger surface roughness leads to a lower yield stress and (ii) the yield stress of pillars with a large surface roughness scales nearly linearly with diameter while that of pillars with smooth surfaces scales exponentially with diameter, the latter of which agrees with experiments. The differences in the yield stress between the two models are attributed to their different plastic deformation mechanisms: in the case of large surface roughness, dislocation nucleation is largely localized near the ends of the pillars; in pillars with smooth surfaces, dislocation avalanches in a more homogeneous manner are observed. This work, which is the first attempt to simulate BCC systems using the CAC method, highlights the significance of the surface roughness in uniaxial deformation of nano/submicropillars.