Orientation dependence of the shape memory properties in aged Ni _45.3Ti_29.7Hf₂₀Pd₅ single crystals

The shape memory properties of Ni_45.3Ti_29.7Hf ₂₀Pd₅ single crystals aged at 550 °C for 3 h and at 600 °C for 48 h were investigated along the [111], [011] and [-117] orientations in compression. The material was stronger along the [-117] orientation compared to the [111] and [011] orientations based on load-biased thermal cycling experiments. The shape memory properties such as reversible strain, temperature hysteresis, critical stress for stress-induced martensite transformation and Clausius-Clapeyron relations were also strong functions of orientation and aging condition (precipitate characteristics). Shape memory effect with no or negligible irrecoverable strain was observed under stress levels as high as 1000 MPa. After aging at 550 °C for 3 h, the maximum reversible strains were 2.2%, 2.7% and 0.7% along the [111], [011] and [-117] orientations, respectively. Aging at 600 °C for 48 h resulted in maximum reversible strains of 2.3%, 3.2% and 0.9% along the [111], [011] and [-117] orientations, respectively. In both cases, similar levels of transformation strain, as a function of orientation, were observed during superelastic testing. The maximum work output reached 27 J/cm³ in the [011] orientation after aging at 550 °C for 3 h.