The effects of process-induced stress on the microstructures and the phasetransformation characteristics of sputtered titanium-nickel thin-film shape-memory alloys

The microstructures and the phase transformation temperatures of sputtered titanium-nickel (TiNi) thin films, both free-standing and attached on diffe rent underlying multi-layer substrates, have been studied. Differences in t he microstructures, such as the lattice constants and relative concentratio ns of TiNi, Ti2Ni and TiNi3 phases, have been observed among the free-stand ing and the attached films, among the films attached on different underlyin g multi-layers and among the films with different relative orders of ageing and release. Not surprisingly, the corresponding phase transformation temp eratures are also different. It is proposed that both process- and substrat e-induced stresses affect the microstructures, hence the phase transformati on characteristics, of the resulting shape-memory thin films.