Deformation characteristics of the intermetallic alloy 60NiTi

The deformation behavior of a Ni-rich Ni55Ti45 (at.%) alloy, commonly known as 60NiTi (as designated inwt.%), was analyzed using neutron and synchrotron x-ray diffraction during in situ isothermal tensionand compression loading, and pre and post-test electron microscopy. The alloy was shown to exhibitremarkable strength and high hardness resulting from a high density of fine Ni4Ti3 precipitates (size~67 nm), which were uniformly dispersed throughout the matrix after a solution treatment and oilquench. The precipitate volume fraction was 55 ± 3%, determined from both the neutron Rietveldrefinement and conventional x-ray measurements. Non-linear stress-strain behavior was observed intension (but not in compression) and was attributed to reversible stress-induced martensite (SIM) thatforms to accommodate the stress as revealed by neutron diffraction measurements. The tensile andcompressive neutron data also showed peak broadening and residual lattice strains. Transmission andscanning electron microscopy revealed stress-induced coarsening of Ni4Ti3 precipitates in both tensionand compression tested samples, but precipitation and growth of the stable Ni3Ti phase was observedonly after tensile testing. Finally, the potential ramifications of these microstructural changes arediscussed