Superelasticity in high-strength heterophase single crystals of Ni$_{51.0}$Ti$_{36.5}$Hf$_{12.5}$ alloy

The effect of precipitated disperse H-phase particles on the thermoelastic B2–B19' martensitic transformation (MT) under compressive load has been studied on [001]-, [236]-, and [223]-oriented single crystals of Ni$_{51.0}$Ti$_{36.5}$Hf$_{12.5}$ (at%) alloy in the initial (as-grown) state. It is established that, in Ni$_{51.0}$Ti$_{36.5}$Hf$_{12.5}$ single crystals containing disperse H-phase particles with dimensions within 125–150 nm at a volume fraction of $\sim$ 30%, neither the critical stresses of martensite formation nor superelasticity strain depend on the orientation. Fully reversible B2–B19' MTs in Ni$_{51.0}$Ti$_{36.5}$Hf$_{12.5}$ single crystals have been observed in tests at external axial stresses up to 1700 MPa and temperatures up to $T_t\sim$ 373 K.