Shape memory effect in sputtered Ti-Ni thin films

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 (similar to 50 at% Ni) were grown by RF magnetron sputtering on a heated sample holder. These films comprised Ti2Ni, TiNi3 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 degrees, 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. (c) 2004 Elsevier B.V. All rights reserved.