Phase fraction, texture and strain evolution in superelastic NiTi and NiTi ±TiC composite investigated by neutron diffraction, Acta Materialia 47

Abstract—Samples of superelastic NiTi and superelastic NiTi reinforced with 10 vol. % TiC particles were deformed under uniaxial compression to 975 MPa while neutron diraction spectra were simultaneously collected. Despite the presence of sti TiC particles, a macroscopic strain of 3 % was obtained in the com-posite on loading and was fully recovered on unloading. The diraction spectra were analyzed by Rietveld refinement that included a spherical harmonic description of the texture and a lattice plane (hkl) dependent formulation of the elastic strain. The experiments provided bulk, phase-specific measurements of the evol-ution of phase fractions, texture and strains during the reversible stress-induced austenite to martensite transformation responsible for the large recoverable strains. For the composite, Eshelby elastic theory is used to predict the discrete phase strains measured by neutron diraction. The observed behavior suggests that the martensite accommodates the mismatch with the transforming austenite (while they co-exist) and the TiC particles (in the case of the composite). # 1999 Acta Metallurgica Inc. Published by Elsevie