Measurements of strain, texture and phase fraction in aged Ni-rich NiTi shape memory alloys by neutron powder diffraction technique under in situ torsional loading

A hollow shaft of superelastic Ti-50.8 atomic percent nickel shape memory alloy has been investigated under torsional load by neutron diffraction. To optimize superelasticity the material was solutionannealed at 850$^{\circ}$C for 15 minutes, water quenched, and subsequently aged at 500$^{\circ}$C for 15 minutes. The torsional load was applied in strain-controlled mode and both torque and torsion angle were measured. The neutron diffraction data were analyzed by the Rietveld refinement program GSAS with a generalized spherical harmonic model for preferred orientation (or texture) to determine phase fractions and crystallographic properties for B2 and B19' during the forward and reverse transformation which are associated with the acquired mechanical hysteresis curve