S. I. Yano, M. Matsuda, Kumamoto University, Kumamoto, Japan; Y. Yamabe-Mitarai, National Institute for Materials Science (NIMS), Tsukuba, Japan; T. Hara, National Institute for Materials Science, Tsukuba, Japan; M. Nishida, Kyushu University, Kasuga, Japan
Ti-Pt alloys of the near-equiatomic composition have been one of the promising materials for high temperature shape memory alloy since they undergo a thermoelastic martensitic transformation from B2 to a B19 type structure at about 1300 K upon cooling. In the present study, the twinning modes in the B19 (2H) martensite are systematically characterized by transmission electron microscopies and electron diffraction experiments. There are three twinning modes, i.e. {111} Type I, <121> Type II and {101) compound twins in the martensite. The {111} Type I and <121> Type II twinnings which were conjugate to each other coexisted in a same martensite variant. The {111} Type I twins are dominantly observed and the (121) Type II twins were less frequently observed. The former twinning was considered to be a lattice invariant shear. In addition to the 2H structure, we find out various long period staking layers such as 6H type martensite. The crystallographical and morphological aspects of twins in the layered martensites are also described.
Summary: In the present study, the twinning modes of the B19 (2H) martensite in the Ti-Pt alloy are systematically characterized by CTEM and electron diffraction experiments. There are three twinning modes, i.e. {111} Type I, <121> Type II and {101) compound twins in the martensite. In addition to the 2H structure, we find out various long period staking layers such as 6H type martensite. The crystallographical and morphological aspects of twins in the layered martensites are also described.
