Substructure characteristics of TiNi shape memory alloys

The substructure of several TiNi shape memory alloys has been analysed by using of TEM in the annealed, work hardened and trained condition. The self-accomodation triangular morphology of B19' martensite is typical for the annealed alloys. After training processes and after cyclic thermal loading of TiNi elements, the substructure changes markedly. After this treatment a very high dislocation density has been detected and the martensitic variants preferentially have the same orientation relationship to the B2 high-temperature phase as in the annealed specimens. Furthermore ghost martensite has been observed in specimens cycled for more than 10 4 times. This phenomenon is connected with the two way shape memory effect.