Hasan, M.; Schmahl, Wolfgang W.; Hackl, K.; Heinen, R.; Frenzel, J.; Gollerthan, S.; Eggeler, Gunther; Wagner, M.; Khalil-Allafi, Jafar; Baruj, A.
Hard X-ray studies of stress-induced phase transformations of superelastic NiTi shape memory alloys under uniaxial load.
In: Materials Science and Engineering A, Vol. 481-482, No. 1-2 C: pp. 414-419
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We examined the texture evolution in a superelastic Ni50.7Ti49.3 (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 0A austenite plane normals are aligned in the rolling direction and 2 0 0A is in the transverse direction. Due to the B2-B19′ lattice correspondence, the 1 1 0A peak splits into four martensite peaks 0 2 0M, over(1, ̄) 1 1M, 0 0 2M and 1 1 1M. The stress-induced martensite is strongly textured from twin variant selection in the stress field with 0 2 0M aligned in the loading direction while the maxima corresponding to over(1, ̄) 1 1M, 0 0 2M and 1 1 1M are at 60°, 67° and 75° from the loading direction. (B19′ unit cell setting: a = 2.87 Å, b = 4.59 Å, c = 4.1 Å, γ = 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.