Zr₅₀Cu₂₅Ni_7.5Co_17.5 high-temperature shape memory alloy with excellent thermal stability and large recovery strain, and the associated microstructural deformation mechanism

In this study, we produced a novel Zr₅₀Cu₂₅Ni_7.5Co_17.5 high-temperature shape memory alloy with the aim of achieving high thermal stability and a good shape memory effect. Differential scanning calorimetry and the compression cycle were utilized to determine the phase transformation temperature and shape memory effect of the alloy, and transmission electron microscopy (TEM) was employed to investigate the microstructure and clarify the corresponding deformation mechanism. We found that the Zr₅₀Cu₂₅Ni_7.5Co_17.5 alloy exhibited excellent thermal stability and achieved the best maximum recovery strain of 6.87% (8% pre-strain) observed to date, making it a promising high temperature shape memory alloy. The TEM results indicated that, during the primary stage of the compression cycle, a small number of the (001) compound twins were de-twinning and numerous contraction twins formed. As the stress increased, increasing numbers of nanoscale (021) and (111) type-I deformation twins formed, and the shift displacement of the type-B planar defect expanded from 3d ~ (001) to 8d ~ (001). Furthermore, the newly found (111) type-I deformation twin and the extension of the type-B planar defect that contributes to the large recovery strain in the Zr₅₀Cu₂₅Ni_7.5Co_17.5 alloy were observed.