In situ neutron diffraction studies of martensitic transformations in NiTi polycrystals under tension and compression stress

Transformation processes in polycrystalline NiTi alloys were studied using two different in situ neutron diffraction techniques. The B2↔B19′ martensitic transformation was investigated in: (i) pseudoelastic test, (ii) cooling under constant compressive stress, and (iii) recovery stress test. Experimental evidence on the martensite variant selection under stress and partitioning of the load and phase fractions among polycrystal grains during the transformation process is discussed and interpreted in terms of the mechanics of the transforming SMA polycrystal with the help of a micromechanical model presented in a companion paper (V. Novak, P. Šittner, in this volume).