Surface and orientation effects on stress-induced hcp-fcc phase transformation in Ti nanopillars

Abstract

An unconventional phase transformation from the hexagonal close-packed (hcp) to the face-centered cubic (fcc) phase in Ti has been reported by previous experimental studies, particularly in micro- and nano-crystals. Here we perform molecular dynamics simulations to investigate the stress-induced hcp-fcc phase transformation with the orientation relationship of <0 0 0 1>hcp||〈0 0 1〉fcc and {101¯0}hcp||{1 1 0}fcc in Ti nanopillars. Our simulation results reveal that the fcc phase prefers to nucleate on a specific side surface {112¯2} of nanopillars under uniaxial tension. The nucleation and growth of fcc-Ti occur via a glide-shuffle mechanism, which involves the 1/6<12¯10> glide of every other two atomic layers along with atomic shuffling. Three different phase interfaces of {101¯1}hcp||{1 1 1}fcc, {101¯2}hcp||{1 1 2}fcc and {101¯0}hcp||{1 1 0}fcc are observed and switched. The surface and orientation effects are further analyzed and indicated to be the dominant factors governing the unconventional phase transformation from hcp to fcc structure at the nanoscale.