Shape memory effect in sputtered Ti–Ni thin films

Abstract The microstructure and electrical transport properties of Ti–Ni granular films have been investigated with X-ray diffraction and DC resistivity measurements, respectively. Samples with the eutectoid composition ( ∼ 50 at % Ni ) were grown by RF magnetron sputtering on a heated sample holder. These films comprised Ti 2 Ni , TiNi 3 and TiNi granular phases, their relative proportions and microstructures critically depending on the substrate temperature. A majoritary metastable TiNi phase was obtained in samples grown at temperatures above 600°, as inferred from the discussion of the X-ray diffraction plots. These crystalline films showed the hysteretic behaviour of the electrical resistance which is attributed to the characteristic shape memory effect of such a binary alloy. Besides, the DC resistivity measurements are accomplished in Joule-heated samples by which efficiently modify their microgranular structure from amorphous to crystalline, or even stabilize the TiNi phase after a flash annealing.