College Park, Maryland      June 6 - 10 , 2004

WP17: Influence of Plastic Deformation on the Stress-Induced Transformation in Superelastic NiTi

C.R. Rathod (AMPAC/MMAE, University of Central Florida), B. Clausen, M.A.M. Bourke (Los Alamos National Laboratory), R. Vaidyanathan (AMPAC/MMAE, University of Central Florida)

The superelastic effect in NiTi occurs due to a reversible stress-induced phase transformation from a cubic B2 austenite phase to a monoclinic B19 martensite phase. There is usually a hysteresis associated with the forward and reverse transformations which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear, a phenomenon called linear superelasticity. Here we report on in situ neutron diffraction measurements during loading and unloading in plastically deformed (up to 11%) NiTi. The experiments relate the macroscopic stress-strain behavior (from an extensometer) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra) in linear superelastic NiTi. The roles of starting texture and cyclic loading following plastic deformation are also investigated. This work is supported by NSF (CAREER DMR-0239512).

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