R-phase formation in Ti39Ni45Cu16 shape memory thin films and bulk alloys discovered by combinatorial methods
R. Zarnetta, D. König, C. Zamponi, A. Aghajani, J. Frenzel, G. Eggeler, A. Ludwig.
Acta Materialia, 57, 4169-4177, (2009)
The combinatorial fabrication and high-throughput characterization of a Ti–Ni–Cu shape memory thin film composition spread led to the discovery of the shape memory alloy Ti39Ni45Cu16, which exhibits a single B2 → R-phase transformation above 25 °C with a thermal hysteresis width <1 K. Here we show that the thin film results correctly predict the phase transformation behavior of bulk material upon cooling from the high temperature phase. For both thin film and bulk, a two-step B2 → R-phase → B19′ transformation was found. The B2 → R-phase transformation can be exploited independently, due to a significant temperature separation of the two transformation steps. The shape memory effect in both thin film and bulk samples is limited due to the two-phase microstructure. Transmission electron microscopy investigations revealed the existence of Ti(Ni,Cu)2 precipitates within the TiNi(Cu) matrix, which are concluded to be responsible for the R-phase formation and separation of the transformation steps.