Grain orientation dependence of ω phase precipitation in ordered body-centered cubic NiTi based alloys

The grain orientation dependence of stress-induced ω phase transformation during tensile deformation was investigated in the ordered body-centered cubic (B2) NiTi based single crystal alloys fabricated by directional solidification. The results show that the alloy with [102] orientation plastically deforms via {112}<111> mechanical twinning and stress-induced ω phase transformation at the twin boundary, while the same alloy with [001] orientation only generates brittle fracture without plastic deformation. The [102] oriented alloy has a much higher Young's modulus and better ductility compared with the [001] oriented alloy. Orientation plays a significant role in {112}<111> mechanical twinning and stress-induced ω phase transformation at the twin boundary, which governs the mechanical properties of the B2 NiTi based single crystal alloys.