High resolution electron microscopy studies on the interface structure of deformed stress induced martensite variants in a Ti–Ni–Nb shape memory alloy

The interfacial structure of deformed stress induced martensite variants in the Ti-44.7 at.% Ni-9 at.% Nb alloy have been investigated by high resolution electron microscopy. Bands conversions were revealed to happen inside the martensite variants to accommodate the macroscopic strain. The evolution of twinning modes from (111̄) Type I to (001) compound Type, <011> Type II and (111) Type I were found. These newly formed (001) deformation twins nucleate and grow inside the substructural bands to perform the coalescence of substructural bands. It also causes the rearrangement of the unfavorably oriented bands. The appearance of the <011> Type II twinning plate seems to eliminate the stress concentration during the coalescence of martensite bands. The (111) Type I twinning plate is also introduced to accommodate the shape deformation in different directions.