Observations of self-accommodated R-phase morphologies in a Ti50.3Ni48.2Fe1.5 shape memory alloy

The self-accommodation morphologies of trigonal R-phase variants exhibited in a Ti50.3Ni48.2Fe1.5 shape memory alloy are observed with orientation contrast (OC) images by a forward scatter detector (FSD). The advantages of studying the self-accommodation morphologies of R-phase variants inside a SEM include easy determination of crystal orientation, higher image resolution, and enabling the study of morphologies on differently orientated grains and at the grain boundary. The twinning planes of a morphology are identified from calculated plane traces by using Euler angles. Analysis on the twinning relationship of a typical herring-bone morphology by this method shows good agreement with previous reports. Observations also include vertical stripe-type morphologies, which were not clearly interpreted previously, and the newfound river-like and large-angle herring-bone morphologies. The newly-formed variants in herring-bone morphology and the intersection between stripe-type and large-angle herring-bone morphologies are also studied. In addition, the self-accommodated R-phase variants are found able to extend across a special high-angle Σ39a boundary.