Structure of martensite in sputter-deposited Ti–Ni thin films containing Guinier–Preston zones Original Research Article

It was found that Guinier–Preston (GP) zones (coherent plate precipitates with a thickness of a few atomic layers) have an influence on the twinning modes of martensite in sputter-deposited Ti–48.9at%Ni thin films. In an equiatomic Ti–Ni thin film (without GP zone) or a thin film with limited GP zone, 〈011〉 type II twins were predominantly observed as a lattice invariant shear. With increasing annealing temperature and/or annealing time, GP zones grow in amount and in size. These GP zones influence the martensitic transformation. They change the twin band width ratio as a lattice invariant shear during martensitic transformation and increase the probability of appearance of (111̄) twinning. When GP zones are sufficient in amount and size, (001) compound twinning was observed as internal defects in the thin film martensite. In general the (001) fine twinning plates are arranged in three orientations with an angle of about 120° between each other. Though there is only one kind of relationship, i.e., (111) twinning, between these (001) twinning regions, three kinds of boundaries exist, i.e., a (111) twinning plane, an averagely approximate (1̄1̄3) plane, or a (111̄) plane. It is believed that these morphologies are also self-accommodated.