Effect of Grain Size of Parent Phase on Twinning Modes of B19' Martensite in an Equiatomic Ti-Ni Shape Memory Alloy
Kumamoto University, Department of Materials Science and Resource Engineering, 2-39-1 Kurokami, Kumamoto 860, Japan
2 Tokin Corporation, 6-7-1 Kohriyama, Taihaku, Sendai 980, Japan
The effect of grain size of B2 parent phase on the twinning modes of B19' martensite in a Ti-50.0 at% Ni shape memory alloy has been studied. The grain size of parent phase was controlled from submicrons to several ten microns by cold-rolling and subsequent annealing. (001) compound twins were dominantly observed in the grain less than 4 μm in diameter, although the (001) compound twinning did not give a solution to the phenomenological crystallographic theory. The triangular self-accommodating morphology of the martensite variants consisting of <011> Type II twins which were theoretically and experimentally recognized as a lattice invariant shear of the present transformation appeared in the whole grain more than 4 μm in diameter. The formation mechanism of the (001) compound twinning in the fine grain is also discussed.
© EDP Sciences