Single and multi-step phase transformation in CuZr nanowire under compressive/tensile loading

A novel stress induced martenistic phase transformation is reported in an initial B2-CuZr nanowire of cross-sectional dimensions in the range of 19.44 × 19.44-38.88 × 38.88 Å2 and temperature in the range of 10-400 K under both tensile and compressive loading. Extensive Molecular Dynamic simulations are performed using an inter-atomic potential of type Finnis and Sinclair. The nanowire shows a phase transformation from an initial B2 phase to BCT (body-centered-tetragonal) phase with failure strain of ∼40% in tension, whereas in compression, comparatively a small B2 → BCT phase transformation is observed with failure strain of ∼25%. Size and temperature dependent deformation mechanisms which control ultimately the B2 → BCT phase transformation are found to be completely different for tensile and compressive loadings. Under tensile loading, small cross-sectional nanowire shows a single step phase transformation, i.e. B2 → BCT via twinning along {100} plane, whereas nanowires with larger cross-sectional area show a two step phase transformation, i.e. B2 → R phase → BCT along with intermediate hardening. In the first step, nanowire shows phase transformation from B2 → R phase via twinning along {100} plane, afterwards the nanowire deforms via twinning along {110} plane which cause further transformation from R phase → BCT phase. Under compressive loading, the nanowire shows crushing along {100} plane after a single step phase transformation from B2 → BCT. Proper tailoring of such size and temperature dependent phase transformation can be useful in designing nanowire for high strength applications with corrosion and fatigue resistance.