The effects of stress-free and stress-assisted ageing at 873 K for 3 h on the crystal microstructure, the B2-B19' martensitic transformation (MT), the critical stress level for the stress-induced martensite formation, and the superelasticity (SE) in Ni-rich Ni51.0Ti37.3Hf12.5 (at.%) single crystals, oriented along the B2 direction, were investigated. For the first time, it is experimentally demonstrated that ageing, under a compressive stress of 150 MPa along the B2 direction, leads to the oriented growth of H-phase particles. The temperature range of SE and the critical stress level for martensite formation are determined by variation in the size (40-150 nm) and the number of crystallographic variants of the H-phase particles. Reversible stress-induced B2-B19' MTs at high levels of applied compressive stress up to 1750-1970 MPa, with the reversible strain of 1.1%, are observed in all investigated Ni51.0Ti37.3Hf12.5 single crystals.
- High-strength single crystals
- Martensitic transformations
- Ni-rich TiNiHf alloys
ASJC Scopus subject areas
- Materials Science(all)