Coherent Subnanometric Plate Precipitates Formed during Crystallization of As-Sputtered Ti-Ni films

Abstract
It is shown by high resolution electron microscopy that coherent plate precipitates with 0.5-1 nm thickness are formed in Ti-rich Ti-Ni thin films when heat treated directly from the sputter-deposited amorphous state near the crystallization temperature. The precipitates are Ti-rich and formed on {100} planes of the B2 matrix phase with perfect coherency. The crystal structure of the precipitate is a body centered tetragonal with the c-axis normal to the habit plane. Owing to the existence of these coherent subnanometric precipitates, the parent phase is greatly strengthened, resulting in very excellent shape memory properties such as 6 % recoverable shape memory strain at the stress level of 300 MPa without any appreciable plastic deformation.