Shape Memory Effect and Superelasticity in [001] Single Crystals of Fe-Ni-Co-Al-Nb(B) Ferromagnetic Alloy

Shape memory effect (SME) and superelasticity (SE) during thermoelastic martensitic transformation (MT) from the FCC high-temperature gamma-phase to the BCT alpha'-martensite are investigated in Fe - 28% Ni - 17% Co - 11.5% Al - 2.5% Nb (Nb) and Fe - 28% Ni - 17% Co - 11.5% Al - 2.5% Nb - 0.05% B (NbB) (at.%) single crystals oriented for tension along the [001] direction after aging at 973 K for 10 h. Non-equiaxial (NiAl) beta-phase particles with thickness d and length l equal to 60-80 and 340-500 nm, respectively, and volume fraction f a parts per thousand yen 3-5% are precipitated in Nb crystals during aging simultaneously with the (FeNiCo)(3)(AlNb) gamma A '-phase with sizes d = 12.5-16.5 nm. It is shown that precipitation of the beta-phase with f a parts per thousand currency sign 3-5% in the crystal volume does not reduce the crystal plasticity, and SME of 4.2% and SE up to 6.5% under loading are observed during thermoelastic gamma-I +/- aEuro(2) MT in single crystals in a wide range of temperatures from 77 to 293 K. The beta-phase is not detected in NbB crystals during aging. It is established that boron in NbB crystals slows down the aging processes: the gamma'-phase particles have sizes 6.5-8 nm. The SME of 4.2% and SE up to 4.0% are observed in NbB crystals at temperatures from 77 to 243 K.