Investigation of the phase state of transformation shear bands in superelastic Ni-rich NiTi shape memory alloys with synchrotron diffraction

摘要

The deformation of superelastic NiTi due to the stress-induced transition from cubic B2 to monoclinic B19′ phase is localised in a Lueders-band-like transformation shear bands (TSB). We investigate the phase state and texture in the bands in-situ using diffraction with high-energy synchrotron-radiation. Residual austenite is observed to persist up to the end of the superelastic plateau in the stress-strain curve. The deformation corresponds to a displacement of the boundary of the TSB. After a certain volume of the specimen has transformed when the boundary has passed by, there is no further change of the crystallographic state of this volume up to the end of the macroscopic stress-strain plateau. The variant orientation texture is different at the surface from that present in the bulk.