THE ROLE OF THE MARTENSITE TRANSFORMATION FOR THE MECHANICAL AMORPHISATION OF NiTi

摘要

Mechanical amorphisation by cold rolling and uniaxial deformation of the intermetallic compound NiTi was studied by TEM and DSC. In cold rolled samples it could be clearly shown that amorphisation occurs and that the amorphous regions recrystallise at T≈350 deg C. In uniaxially deformed material a microstructure similar to that of cold rolled samples and a DSC-peak at the same temperature was found. In the TEM, extended amorphous regions could only be identified after a moderate heat treatment at 250 deg C. After deformation at temperatures above room temperature, a considerably lower degree of amorphisation was found, and the fraction of amorphous volume was found to depend on the martensite transition temperature of the material.