NiTi shape memory marformed alloy studied by electron beam precession TEM orientation mapping method

Abstract

Severe plastic deformation by cold-rolling in martensitic state was applied to Ni50.4Ti49.6shape memory alloy. Received materials with 17, 20, 25, and 35% deformation were further annealed at 450 °C for 15 min. After such treatment hardness of this alloy increased significantly reaching 365 HV0.5 for highest deformation degree. Calorimetric studies revealed two-stage and two-step character of martensitic transformation occurring in all specimens. Nanocrystalline structure with average grain size 53, 34, 28, and 24 nm was obtained. In material with 35% of deformation amorphous regions containing a nuclei of B2 parental phase with average size of 5 nm were observed. To determine the crystallographic orientation of observed nanograins and for better phase analysis, electron beam precession transmission electron microscopy orientation mapping was performed.