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We examined the texture evolution in a superelastic Ni 50.7 Ti 49.3 (numbers indicate at.%) alloy under applied uniaxial stress using high-energy synchrotron X-ray diffraction in transmission geometry. Texture information is identified from the intensity variations along Debye-Scherrer rings recorded on area detector diffraction images. The 1 1 0 A austenite plane normals are aligned in the rolling direction and 2 0 0 A is in the transverse direction. Due to the B2-B19 lattice correspondence, the 1 1 0 A peak splits into four martensite peaks 0 2 0 M ,1 1 1 M , 0 0 2 M and 1 1 1 M . The stress-induced martensite is strongly textured from twin variant selection in the stress field with 0 2 0 M aligned in the loading direction while the maxima corresponding to1 1 1 M , 0 0 2 M and 1 1 1 M are at 60 • , 67 • and 75 • from the loading direction. (B19 unit cell setting: a = 2.87Å, b = 4.59Å, c = 4.1Å, ␥ = 96.2 • ). A comparison between the experimental and recalculated distribution densities for the polycrystalline NiTi shows a reasonable agreement. In addition, we compare our experimental results with a micromechanical model which is based on total energy minimization. In this case, we also observe an overall agreement.

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We make use of a micromechanical model for polycrystalline shape memory alloys, whose main focus is the orientation distribution of the martensitic low symmetry variant. By energy minimization, the internal reorientation of martensite can be predicted. Hysteresis effects are included via the hypothesis that changes in the orientation distribution are connected to energy dissipation. From these considerations, we obtain evolution equations for the orientation distribution in terms of the thermomechanical driving forces. Comparing our model to results from synchrotron diffraction experiments, good agreement is found between experimentally observed and analytically predicted orientations of austenite and stressinduced martensite.

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