Shape Memory Effect and Superelasticity of [001]-Oriented FeNiCoAlNb Single Crystals Aged under and without Stress

The two-step ageing of Fe-28Ni-17Co-11.5Al-2.5Nb (at.%) single crystals under and without stress, leads to the precipitation of the gamma '- and beta-phase particles. Research has shown that gamma-alpha ' thermoelastic martensitic transformation (MT), with shape memory effect (SME) and superelasticity (SE), develops in the [001]-oriented crystals under tension. SE was observed within the range from the temperature of the start of MT upon cooling M-s, to the temperature of the end of the reverse MT upon heating A(f), and at temperatures from A(f) to 323-373 K. It was found that at gamma-alpha ' MT in the [001]-oriented crystals, with gamma '- and beta-phase particles, a high level of elastic energy, Delta G(el), is generated, which significantly exceeds the energy dissipation, Delta G(dis). As a result, the temperature of the start of the reverse MT, while heating A(s), became lower than the temperature M-s. The development of gamma-alpha ' MT under stress occurs with high values of the transformation hardening coefficient, Theta = d sigma/d epsilon from 2 to 8 GPa and low values of mechanical Delta sigma and thermal Delta T-h hysteresis. The reasons for an increase in Delta G(el) during the development of gamma-alpha ' MT under stress are discussed.

Automated summary

Research has shown that the two-step ageing of Fe-Ni-Co-Al-Nb alloy single crystals under stress leads to the development of the gamma-alpha ' thermoelastic martensitic transformation (MT) with superelasticity (SE).