Martensitic transformation of cold-rolled and annealed Ti 50Ni40Cu10 shape memory alloy

Abstract

This study investigates the cold-rolling effect on the formation of Ti(Ni, Cu)2 precipitates and on the change of transformation temperatures for hot-rolled (HR)/annealed (HRA) and HR/cold-rolled/annealed (CRA) Ti 50Ni40Cu10 specimens. Particle-like Ti(Ni, Cu)2 precipitates formed in CRA are more numerous and smaller than plate-like Ti(Ni, Cu)2 precipitates formed in HRA and thus the hardness and storage modulus of the former are higher. The broader transformation peaks exhibited in CRA compared to HRA can be explained by the assistance of the tensile stress field around the plate-like Ti(Ni, Cu) 2 precipitates. The different transformation peak temperatures of B2→B19 and B19→B19′ in between HRA and CRA result from the different Cu content in the matrix. A relaxation peak appears in CRA with the activation energy of 64.4 kJ/mol. The cold-rolling process may be an important factor in enhancing the appearance of the relaxation peak. © 2009 The Japan Institute of Metals.