Twins in the 9R-martensite of Ti50.0Pd43.0Fe7.0 shape memory alloy were investigated by means of transmission electron microscopy. It was found that there were 4 twinning modes: {11¯4}9R type-I, <¯591>9R type-II, {105}9R compound and {001}9R compound twins. The {11¯4}9R type-I and the <¯591>9R type-II twins were considered to involve lattice-invariant shear in the 9R-martensite which continuously coexisted with 2H-martensite. On the other hand, the 2 twins and the {105}9R compound twin could be regarded as being variant accommodation twins in the region consisting only of 9R-martensite. The irrational nature of the type-II twin boundary (A:B-type pair) was also observed in the edge-on state by means of high-resolution electron microscopy. The boundary was gradually and randomly curved with strain contrast.

Crystallography and Morphology of Twins in 9R Martensite in Ti-Pd-Fe Shape Memory Alloy. S.Ii, M.Nishida, T.Hara: Scripta Materialia, 2002, 46[7], 549-54