On the stress-assisted aging in NiTiHfPd single crystal shape memory alloys

The effects of aging under compressive stress of 300 MPa on the shape memory properties and microstructure of [1¯ 17]-oriented Ni45.3Ti29.7Hf20Pd5 single crystals were studied. It was revealed that stress-assisted aging resulted in 4 variants of the H-precipitates in contrast to 6 variants observed after stress-free aging. It was revealed that precipitate properties and martensite morphologies strongly depend on aging conditions. As a consequence of the aligned precipitates and generated internal stress, two-way shape memory effect (with up to 0.55-0.8% strain) and higher recoverable strains were observed in Ni45.3Ti29.7Hf20Pd5 single crystals after stress-assisted aging.