R. Vaidyanathan et al., Texture, strain, and phase-fraction measurements during mechanical cyclingin superelastic NiTi, MET MAT T A, 32(3A), 2001, pp. 777-786
Superelastic NiTi was subjected to simultaneous neutron diffraction and uni
axial compressive cycling between 10 and 980 MPa. The objective was an in-s
itu investigation of the evolution of the stress-induced, reversible transf
ormation between austenite and martensite, to determine the cause of the ch
anges in the macroscopic stress-strain response with cycling. Rietveld refi
nement was used to analyze the neutron spectra and quantify the phase fract
ion, texture, and elastic strain. The average phase strain in the mechanica
lly loaded austenite (at a given stress) remained unaltered during the 100
load-unload cycles. However, differences in both the volume fraction and te
xture of austenite and martensite were noted as cycling progressed, suggest
ing that these factors are responsible for the changes in the macroscopic s
tress-strain response of NiTi with mechanical cycling.