Texture after ECAP of a cube oriented Ni single crystal W. Skrotzki and B. Klöden Institut für Strukturphysik, Technische Universität Dresden, D-01062 Dresden, Germany To model the plastic behaviour of polycrystals it is necessary to understand the plastic response of each crystallite with respect to its neighbourhood characterized by the local orientation, grain size, grain shape and grain shape preferred orientation. This is a complex problem to solve and only recently a tomographic technique based on high-energy synchrotron radiation has been developed to in-situ monitor orientational changes grain resolved [1, 2]. However, so far this highly promising technique is limited to grain sizes larger than several μm and, due to fragmentation during deformation, to low strains. Hence, to study high deformations leading to ultrafine microstructures with grain sizes smaller than 1 μm, single crystal deformations under differently constrained conditions are very helpful, although the grain neighbourhood is not correctly accounted for. Nethertheless, valuable informations on the orientation dependent development of macro- to microscale inhomogeneities and their effect on texture formation can be obtained. Compared to a polycrystal, it is an important advantage that the starting orientation is clearly defined. Impressive examples are given for example for plane strain compression [3] of Al single crystals. In the case of ECAP such a basic study will be extended here to the cube orientation which is of particular kind because it is metastable during ECAP deformation of fcc metals [4] but preferably forms during recrystallization [5]. The study will focus on the heterogeneity of orientation spreading taking place from the top to the bottom of the ECAP billet. Preliminary results on the inhomogeneity of microstructure and texture have been given elsewhere [6, 7], an extended version with focus on the heterogeneity of microstructure is in preparation. A cube oriented bar of (10 x 10 x 100) mm 3 was cut by spark erosion from a Ni single crystal (4N purity) grown by the Bridgman technique. Measurements by electron back scatter diffraction (EBSD) were carried out to verify the single crystal quality. Punctual orientations measurements at 18 locations on the polished {100} surfaces reveal non-systematic deviations from the perfect cube orientation. The maximum deviation was 4.5° with a mean value of 2° suggesting the existence of very low angle boundaries. One pass ECAP was carried out with a Zwick 200 kN screw driven machine. The channels of the ECAP die had a square cross section of (10 x 10) mm 2 meeting at an angle Φ = 90°. All corners and edges of the die were sharp. The ECAP was done at room temperature with a crosshead speed of 1 mms -1 using MoS 2 as lubricant. To examine the texture heterogeneity after ECAP deformation, the local texture was analyzed by diffraction of high-energy synchrotron radiation using beam line BW5 (100 keV) at DESY-HASYLAB. The sample for local texture measurements with synchrotron radiation was a pin of (1 x 1 x 10) mm³ taken from the centre of the billet with the long sample axis parallel to the Y-axis (normal to the top of the billet). The texture was measured at 5 positions along the Y-axis. Details about the synchrotron texture measurements are given in [8]. Three pole figures, namely (200), (220) and (111), were used to calculate the orientation distribution function (ODF) with the harmonic method. The sample coordinate system to calculate the ODFs was chosen with X, Y, Z parallel to the extrusion direction, normal and transverse direction, respectively. In ECAP, a billet is deformed in a narrow deformation zone at the plane of intersection of two die channels of equal area cross-section and the strain mode approximates closely to simple shear [9]. However, mainly because of friction at the die walls the deformation mode operative in the ECAP process is more complex. Consequently, microstructure and texture formation is non-uniform across the billet mainly resulting in a gradient from the top to the bottom part. This has been clearly demonstrated by the present authors, e.g. [4]. Fig. 1 shows that this also holds for the Ni single crystal deformed by ECAP. In the upper part the texture is characterized by a rotated cube component with +ϕ 1 rotation about the transverse direction corresponding to a sinestral shear in the intersection plane. Moreover, a weaker split C E exists with one of the partial components predominating. The central part of the billet (3 to 7 mm from the top) only consists of the split C E with the partial components being of different intensity. At 7 mm the partial components are displaced asymmetrically with respect to the ideal C E component. In the bottom part the texture consists of an almost unrotated cube component plus the split C E with unequal partial components. 753