Shape Memory Effect and Superelasticity in High-Strength FeNiCoAlTiNb Single Crystals

The effect of two-stage ageing in a stress-free state and under tensile stress on the precipitation processes of dispersed particles, temperature range of gamma-alpha' martensitic transformations (MT), superelasticity and shape memory effect was investigated on [001]-oriented single crystals of the Fe-28% Ni-17% Co-11.5% Al-2.5% TiNb (at %) alloy. It was shown that two-stage ageing leads to simultaneous precipitation of gamma'- and beta-phase particles. beta-phase particles were not found to inhibit the gamma-alpha' MT and led to the appearance of a tensile two-way shape memory effect (TWSME), which was 3.8% in stress-assisted aged crystals. The reasons for the appearance of a TWSME were discussed.