Nanoscale amorphization of severely deformed NiTi shape memory alloys

NiTi shape memory alloys deformed by high-pressure torsion (HPT) were investigated by transmission electron microscopy. Radial sections of the HPT discs facilitate the analysis of nanoscale amorphous and crystalline phases. Ultrathin amorphous ribbons forming at grain boundaries are intersected by shear bands. At higher deformation they transform into thicker amorphous bands containing nanocrystalline debris. In the case of planar sections, the presence of amorphous phase can be obscured by overlapping nanocrystals leading to moiré contrast.