J. Phys. IV France 112 (2003) 639
Neutron scattering study on equi-atomic TiNi alloyT. Ohba1, T. Fukuda2, T. Tabata2 and T. Kakeshita2
1 Department of Materials Science, Shimane University, Nishikawatsu, Matsue 690-8504, Japan
2 Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
In TiNi alloy systems, there are three transformation paths. Fe added alloy, TiNi(Fe), transforms into the R phase whose crystal structure is similar to AuCd phase. Cu added alloy, TiNi(Cu), transforms into the orthorhombic phase which is called B19. They transform into monoclinic martensite called BI9' when temperature is further lowered. Without third element addition, quenched Ti 50Ni 50 transforms into Bl9' direct. The crystal structure of the monoclinic phase can be described with a combination of alternative [ 01 ] movements on the (011) plane and [ 00] movements on the (0 l) plane. Phonon behavior in martensite materials is attractive for the transformation mechanism. Alternative motion of [ 01 ] on (011) in TiNi corresponds to TA 2 phonon softening at the Brillouin zone boundary. Phonon dispersion behavior of  TA 2 in equi-atomic Ti 50Ni 50 was measured and softening around q ~ 1/3 is reported rather than at the zone boundary.
© EDP Sciences 2003