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Materialien/Werkstoffe Poster: Do., 13:00–15:30 D-P387
In-situ investigation of superelasticity of NiTi under uniaxial load with hard
x-rays
Mahamudul Hasan 1,2 , Wolfgang Schmahl 1 , Klaus Hackl 3 , Rainer Heinen 3 ,
Jan Frenzel 4 , Susanne Gollerthan 4 , Gunther Eggeler 4 , Martin Wagner 4 ,
Jafar Khalil-Allafi 5
1 Ludwig-Maximilian Universität, Department für Geo- und Umweltwissenschaften,
Sektion Kristallographie,Theresienstr. 41, 80333 München, Germany – 2 Ruhr-
Universität Bochum, Fakultät für Geowissenschaften,Universitätsstr. 150, 44780
Bochum – 3 Ruhr-Universität Bochum, Institut für Mechanik, Lehrstuhl für Allgemeine
Mechanik Universitätsstr. 150, 44780 Bochum, Germany – 4 Ruhr-Universität Bochum,
Institut für Werkstoffe, Universitätsstr. 150, 44801 Bochum, Germany – 5 Sahand University
of Technology, Faculty of Materials Engineering, Tabriz, Iran
We investigated the local textural evolution in a superelastic Ni50.7Ti49.3 alloy under
an 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 original textures
of the cold rolled B2 austenite and that of the stress-induced B19’ martensite
are quantitatively related to the features of the superelastic plateau in the stress-strain
curve. The {110}A austenite plane normals are aligned in the rolling direction and
{200}A is in the transverse direction. Due to the B2-B19’ lattice correspondence, the
{110}A peak splits into four martensite peaks {020}M , {-111}M , {002}M and {111}M
[1]. The stress-induced martensite is strongly textured due to twin variant selection
in the stress field with {020}M aligned in the loading direction while the {002}M and
{111}M maxima are at 67 o and 75 o from the loading direction. (B19’ unit cell settings:
a = 2.87 ˚A, b = 4.59 ˚A, c = 4.1 ˚A, γ = 96.2 o ). 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 [2] and we find again reasonable
agreement.
[1] W.W. Schmahl et al., Mat. Sci. Eng. A 378, (2004), 81.
[2] K. Hackl, M. Schmidt-Baldassari, W. Zhang, Mat. Sci. Eng. A 378, (2004),503.
Keywords: Texture evolution, superelasticity, stress-induced martensite, cold rolled B2
austenite, NiTi.