The fabrication and characterization of new NiCuTiZrFe high entropy shape memory alloys with exceptional functionality

In the present study, the multicomponent Ni ₂₅Cu ₂₅Ti _35-XZr ₁₅Fe _X (X = 3, 5, 7, 10) high-entropy shape memory alloys (HESMAs) were designed. Moreover, the effect of Fe content on the microstructural features, martensitic transformation behaviors and mechanical/functional performances was investigated. The results demonstrated that the as-casted NiCuTiZrFe HESMAs exhibited the typical dendritic structures. The as-casted Ni ₂₅Cu ₂₅Ti _35-XZr ₁₅Fe _X HESMAs with the lower Fe content consisted of B2 phase and HCP phase. With Fe content increasing, the amount of FCC phase gradually increased. In proportion, the fracture strength of as-casted Ni25Cu25Ti32Zr15FeX HESMAs continuously decreased from 2019 MPa to 1364 MPa, meanwhile the microhardness was also reduced from 593.33 HV to 146 HV, as Fe content increased from 3.0 at.% to 10.0 at.%. In contrast, the as-casted Ni ₂₅Cu ₂₅Ti ₃₂Zr ₁₅Fe ₃ HESMAs exhibited a superior combination of higher compressive strength and microhardness as well as the excellent superelasticity with the recoverable strain of 7 %. Furthermore, the Ni ₂₅Cu ₂₅Ti ₃₂Zr ₁₅Fe ₃ HESMAs demonstrated the good superelasticity stability, which can be ascribed to the saturated higher density dislocations during the initial compressive cycles.