P. J. S. Buenconsejo, R. Zarnetta, D. Koenig, A. Savan, S. Thienhaus, A. Ludwig, Ruhr-University Bochum, Bochum, Germany
The effects of elements with limited solubility in the Ti-Ni (B2) phase, such as W and Ag, was investigated by combinatorial sputter-deposition methods and high throughput characterization techniques. The addition of Ag is attractive due to its antibacterial function, whereas W is attractive as a heavy element that can give high radio-opacity for Ti-Ni based medical devices. Continuous composition spread materials libraries were deposited on SiO2/Si substrates for both ternary systems using a wedge-type multilayer approach, sputtered from elemental targets and subsequent annealing at 500°C for 1 hour. XRD measurements revealed that for both systems the amount of Ag and W dissolved in the B2-phase was less than 2 at.%, above which they formed secondary phases. For Ti-Ni-Ag the Ag combined with excess Ti forms Ti2Ag and TiAg precipitates, whereas for Ti-Ni-W the excess W precipitated as β-W. For this reason both systems behaved as a pseudo-binary Ti-Ni system where the transforming region was mainly limited by the presence of large amount of Ti2Ni and TiNi3 precipitates in the Ti-rich and Ni-rich regions, respectively. Furthermore it was revealed that the transformation pathway measured using temperature-dependent resistivity measurements (R(T)) in a temperature range of -20 °C to 120 °C was dominated by B2-R-phase transformations for both ternary systems, when the solubility limit for Ag and W were exceeded. It is suggested that introducing elements with limited solubility in the Ti-Ni (B2) phase is an effective method to induce B2-R transformation.
Summary: The effects of elements with limited solubility in the Ti-Ni (B2) phase, such as W and Ag, was investigated by combinatorial sputter-deposition methods and high throughput characterization techniques. Results showed that the addition of W and Ag to Ti-Ni was effective to induce the B2 to R phase transformations.
