3R and 14M martensitic transformations in as-rolled and annealed Ni64Al34.5Re1.5 shape memory alloy

Martensitic transformation of as-rolled and 1323 K × 1 h annealed Ni64Al34.5Re1.5 (NiAl–1.5Re) shape memory alloy (SMA) is investigated. For as-rolled NiAl–1.5Re alloy, TEM and EPMA results indicate both 14M and 3R martensites are observed at the room temperature. 14M is formed in the precipitate-free zone which is a Ni-depletion region and 3R is formed in the matrix which is a Ni-enrichment region. XRD and partial-cycle DSC testing results show that the higher temperature peak of the DSC cooling curve is B2 → 14M and the lower one is B2 → 3R. Hardness tests show that 14M hardness is higher than that of 3R. For annealed NiAl–1.5Re alloy, only B2 ↔ 3R can be observed. The critical value for the formation of 14M martensite in NiAl–1.5Re alloy is about 63.6 at.% Ni, as compared to 63.0 at.% Ni for Ni–Al binary SMAs.

Research highlights▶ For as-rolled Ni64Al34.5Re1.5 (NiAl–1.5Re) shape memory alloy (SMA), both B2 → 14M and B2 → 3R transformations are identified with the former one appearing at higher temperature. ▶ For annealed NiAl–1.5Re SMA, only B2 ↔ 3R transformation can be observed. ▶ The critical value for the formation of 14M martensite in NiAl–1.5Re SMA is about 63.6 at.% Ni, as compared to 63.0 at.% Ni for Ni–Al binary SMAs.