Stress-induced martensitic transformation of Cu50Zr50 shape memory alloy optimized through microalloying and co-microalloying

The stress-induced martensitic transformation of Cu50Zr50 at. % shape memory alloy was tuned through microalloying and co-microalloying. The effect of microalloying elements Co or Ni individually or combined (i.e., co-microalloying) was investigated and compared at the macro- and nanoscale. From nanoindentation experiments, change in the slopes of (P/h)-h curves, plastic index and recovery ratio after annealing were investigated: partial replacement of Cu by 1 at. % Ni was observed to promote twinning while for 1 at. % Co the twinning propensity decreased and co-microalloying using 0.5 at. % Co and Ni had an intermediate effect. The recovery ratio of the Cu50Zr50 alloy, calculated from the volume change of a residual indent after annealing at 400 °C for 5 min after annealing at 400 °C for 5 min increased from 15.6% to 19.5% when substituting Cu by 1 at. % Ni. These results, obtained at the nanoscale, are in agreement with macroscale test observation, namely, differential scanning calorimetry and x-ray diffraction. Therefore, microalloying opens up possibilities for the development of more cost-effective CuZr alloys, with a view to develop commercial actuators that could replace costly NiTi alloys in the near future