The effect of ω-phase precipitation on thermal- and stress-induced martensitic transformations in Ni47.5Fe15Ga27.5Co10 single crystals

The key role of ω-phase nanoparticles in determining the properties of [001]-oriented Ni47.5Fe15Ga27.5Co10 single crystals under compression has been established. The ω-phase particles strongly affect the martensitic transformation temperature, as well as their thermal stability, martensite yield strength, and superelasticity temperature range. Dissolution of the ω-phase after annealing at 1448 K for 1 h followed by quenching led to a low martensite yield strength (1025 MPa at 302 K) and high-temperature martensitic transformations (Ms = 400 K) with low thermal stability of Ms during overheating to 523 K. Precipitation of ω-phase nanoparticles during aging at 523 K for 15 min increased the martensite yield strength (up to 1550 MPa) and decreased the martensitic transformation temperatures (up to 350 K), but improved the thermal stability of Ms during overheating. The Ni47.5Fe15Ga27.5Co10 single crystals (as-grown and aged at 573 K for 15 min) containing ω-phase nanoparticles demonstrated a wide range of high-temperature superelasticity, from 373 to 573 K.