Sputter deposition of NiTi to investigate the Ti loss rate as a function of composition from cast melted targets

Off-stoichiometric NiTi sputtering targets were manufactured by cast melting in order to sputter Ni-rich NiTi thin films. Crystalline samples, which reveal a martensitic transformation, were fabricated by magnetron sputtering and subsequent thermal treatment. A systematic investigation to determine the deviation between target and substrate composition was carried out by means of microprobe analysis. Typical loss rates in sputtering targets with Ti content higher than 49.5 at.% were in the order of 4.3 at.%, whereas more Ni-rich targets revealed a Ti loss rate of only 0.5–1.5 at.%. Sacrificial layer technique was applied to obtain free-standing NiTi films. Transformation temperatures and hysteresis properties of the martensitic transformation were characterised by differential scanning calorimetry (DSC) but showed only minor differences concerning composition. Free-standing films obtained from the Ti–53.1 Ni–46.9 at.% sputtering target revealed superelastic properties at 40 °C as demonstrated by tensile testing.