CRYSTALLIZATION AND MARTENSITIC-TRANSFORM ATION OF SPUTTER-DEPOSITED TI-NI THIN-FILMS

Ti-Ni alloy films were deposited on quartz substrates by sputtering in argon atmosphere, using a sputtering target of an equiatomic TiNi all oy. The composition of the films were determined by electron probe mic ro-analysis using a calibration line prepared from bulk samples of wel l-established compositions. Since it was found that the Ti content in a deposited film was less than that of the target material, the film c omposition was controlled by placing Ti pieces on the target and chang ing their sizes. In this way it was successful in obtaining films with various compositions. Transmission electron microscope observation sh owed that the as-deposited films are amorphous when the substrate temp erature is kept below 423 K during sputtering, and that they are cryst allized when the specimens are heated above 708 K. By the heat treatme nt at temperatures above 708 K, Ti2Ni precipitated in the Ti-46.8 at.% Ni and Ti-48.4 at.%Ni films, and Ti3Ni4 precipitated in the Ti-51.4 at .%Ni film, but no precipitation occurred in the Ti-50.0 at.%Ni film. T he martensitic transformation in these films were investigated by diff erential scanning calorimetry and electron microscopy. The R-phase tra nsformation occurred reversibly on cooling and heating the films in th e electron microscope. It was confirmed by constant load thermal cycli ng tests that the films show very good shape memory.