Hard X-ray studies of stress-induced phase transformations of superelastic NiTi shape memory alloys under uniaxial load

M. HASAN; W. W. SCHMAHL; K. HACKL; R. HEINEN; J. FRENZEL; S. GOLLERTHAN; G. EGGELER; M. WAGNER; J. KHALIL-ALLAFI; A. BARUJ

Bochum, Alemania

Congreso; European Symposium on Martensitic Transformations ESOMAT 2006; 2006

Ruhr Universitaet Bochum, Alemania

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 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 0A 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 0M aligned in the loading direction while the maxima corresponding to [-1 1 1]M, [0 0 2]M and [1 1 1]M are at 60 deg., 67 deg. and 75 deg. from the loading direction. (B19’ unit cell setting: a = 2.87 Angstrom, b = 4.59 Angstrom, c = 4.1 Angstrom, gamma = 96.2 deg.). 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.