Deformation mechanisms in nanotwinned nanopillars/nanotubes in body-centered cubic tungsten

Coherent twin boundaries (CTBs) are known to play a significant role in deformation mechanisms of metallic nanopillars/nanotubes. While numerous molecular dynamics (MD) studies have been devoted to investigating nanotwinned face-centered cubic (FCC) nanopillars, very few MD work in the literature concern the body-centered cubic (BCC) metallic nanopillars containing CTBs. On the other hand, recent studies confirmed that nanotwinned nanopillars/nanotubes in BCC systems have mechanical properties distinct from those in FCC lattices. Here, using MD simulations, we explore the uniaxial deformation mechanisms of nanopillars/nanotubes in BCC tungsten, as a function of cross-sectional area/shape and CTB spacing. Results show a strong tension-compression asymmetric deformation in nanotwinned BCC nanopillars, with the smallest CTB spacing (= 1 nm) leading to unusual mechanical responses than those with larger CTB spacing. Particularly under tensile loading, the detwinning process on {112} planes results in the formation of incoherent twin boundaries on {111} planes. This process hasn’t been observed in any FCC metal, nor in BCC metals such as Fe.