Transformation behavior and superelasticity of TiZrHfNiCoCu multi-component high-temperature shape memory alloys

Highlights: • The area fraction of second phase increased with the increased in the amount of (TiZrHf). • The martensitic transformation start temperature increased with the increase in (TiZrHf). • Solution treated 50(TiZrHf) and 50.5(TiZrHf) HTSMAs showed clear superelasticity. -- Abstract: Multi-component (TiZrHf)₁Ni_1.50Co_0.60Cu_0.90, (TiZrHf)₁Ni_1.48Co_0.58Cu_0.88, (TiZrHf)₁Ni_1.45Co_0.57Cu_0.86, and (TiZrHf)₁Ni_1.40Co_0.54Cu_0.82 high-temperature shape memory alloys (HTSMAs) were prepared by arc-melting and then microstructures, transformation temperatures, phase constituents and superelasticity were investigated by scanning electron microscope observation, differential scanning calorimetery, X-ray diffraction and dynamic mechanical analysis in tensile mode, respectively. The microstructure of solution treated TiZrHfNiCoCu HTSMAs specimens consisted of (TiZrHf)(NiCoCu)-type matrix and (TiZrHf)₂(NiCoCu)-type second phase. The area fraction of the second phase increased from 1.7% to 17.2% with the increased in (TiZrHf) content from 50 at% to 52 at%. Martensitic transformation start temperature of the solution treated specimens increased from 53.5 °C to 188.7 °C with the increase in (TiZrHf) content from 50 at% to 52 at%. TiZrHfNiCoCu HTSMAs showed clear superelasticity in the solution treated state. The superelastic recovery strain of solution treated TiZrHfNiCoCu HTSMAs was in the range of 4.2–4.6% depending on the alloy composition.