New insights on improving the strain recovery characteristics of the Cu-Al-Ni high-temperature shape memory alloy

This study introduces a novel approach to enhance the strain recovery characteristics of Cu-Al-Ni high-temperature shape memory alloys by introducing Sr elements to optimize the proportion of martensitic variants. First-principles calculations show that adding Sr can effectively reduce the stacking fault energy, which facilitates the transformation from the 2 H to the 18 R phase. Subsequently, the proportion of the 18 R phase significantly increases to 83.7 % in the Cu-Al-Ni-Sr alloys. Meanwhile, we identified a unique alternating structure with the co-existence of two different martensite phases, strongly supporting that Sr addition promotes extensive 2H-to-18R phase transformation and enhances the shape memory effect. Compression tests revealed that the Sr doping improved the shape memory effect recovery strain from 2.6 % to 5.0 % with 8 % pre-strain, while reducing irreversible strain. These findings demonstrate that tailoring martensite variant ratios through specific alloying can significantly enhance the strain recovery properties of Cu-Al-Ni alloys, offering a new strategy for developing high-performance shape memory alloys.