Effects of ageing on microstructure and superelastic behavior of [110]-oriented Ni45.3Ti29.7Hf20Pd5 single crystals

The effects of ageing at 773 K for 3 h on microstructure and superelastic behavior in B2-B19' thermoelastic martensitic transformations of Ni45.3Ti29.7Hf20Pd5 (аt%) single crystals were investigated in this study. Ageing introduced nanoscale H and H′ phase precipitates, which resulted in a decrease of B2-B19' transformation temperatures, a dispersion hardening of the B2 phase and a twofold increase in the superelasticity range (up to ΔТSE=200 K) as compared with quenched crystals. In aged single crystals, reversible thermoelastic transformations with an extremely high critical stress level (σcr=1500 MPa) and reversible strain up to 1.8% were obtained at elevated temperatures (450 K).