Control of the twinning propensity of Cu50Zr50 shape memory alloy optimized through microalloying and co-microalloying

Control of the twinning propensity Cu50Zr50 shape memory alloy optimized through microalloying and co-microalloying
F. De Luca1, P. Nnamchi2, A. Younes2, A.T. Fry1, S. González2
1 National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK
2 Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK

Abstract:
The effect of microalloying with Co or Ni individually or co-microalloying on the twinning propensity for stress-induced martensitic transformation of Cu50Zr50 at. % was investigated at different levels (i.e., nano and macro). Investigation at nano level will be performed from nanoindentation experiments by analysing the change in the slopes of (P/h)-h curves, plastic index and recovery ratio after annealing. Partial replacement of Cu by 1 at. % Ni promotes twinning but for 1 at. % Co the twinning propensity decreased. Co-microalloying using 0.5 at. % Co and Ni had an intermediate effect. Partial replacement of Cu by 1 at. % Ni from the parent Cu50Zr50 alloy, enabled to improve the recovery ratio after annealing at 400C for 5 min, from 15.6 % to 19.5 %. The results, obtained at the nanoscale, agree with those at macroscale (i.e., 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.