Deposition and characterization of TiNi-base thin films by sputtering

Chemical compositions, crystallography, microstructure and phase transformation behavior of TiNi-base alloy films grown by R.F. magnetron sputtering have been investigated. Effects of alloying elements such as Cu and Fe on film crystallography and properties are studied. Due to the non-equilibrium characteristic of sputter deposition, as-deposited TiNi-base films prepared are in a non-equilibrium, amorphous state. To yield crystalline structures and desirable phase transformation behaviors, post-deposition annealing in vacuum at 600 degrees C for 1 h is needed. Phase transformation behavior is evaluated by a differential scanning calorimeter and results indicate a typical single-stage transformation in annealed binary films (Ti-48.9 at.%Ni and Ti-41.8Ni). For the Ti-36.6Ni-10.4Cu film, a two-stage transformation is revealed. The single-stage transformation takes place between the B2 parent phase and M (monoclinic) martensite or R (rhombohedral) phase, while the two-stage transformation occurs in a sequence of B2 phase to O (orthorhombic) phase to M phase on cooling and vice versa on heating. Yet, an imperfect phase transformation is found in the Ti-45.4Ni-6.3Fe film for the temperature range examined. Transformation temperatures as well as energies involved in the transformations are in general relatively lower than those of the target. Transformation peak-temperature hystereses of the film are also smaller than that of the target, implying a beneficial characteristic of fast response for shape memory effect. (C) 2000 Elsevier Science S.A. All rights reserved.