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INTRODUCTION

IN the last decade, alloys based on the intermetallic
-TiAl phase have been developed to some maturation for application as high-temperature lightweight alloys up to around 750 °C.[1,2,3] As with other structural materials, control of texture might significantly improve the mechanical properties, in particular if the envisaged component is uniaxially loaded. In this respect, the anisotropic properties of the
-TiAl phase with a tetragonal L10 structure should be pointed out, which, e.g., are reflected in the Young’s moduli of 133 GPa in the [001] and 216 GPa in the 111 directions at room temperature.[4] Furthermore, the desired lamellar microstructures of
-TiAl alloys consist of stacks of parallel platelets with crystallographically oriented interfaces,[3,5] giving rise to strong anisotropies of textured lamellar materials.[3,6] For these reasons, the different processing routes are either aimed at obtaining strong textures, e.g., as by directional solidification,[7] or to avoid preferential orientations, both offering advantages for specific applications. The texture development in
-TiAl alloys during hot working might be characterized by some peculiarities in comparison to the behavior of solid-solution phases. These include the occurrence of perfect dislocations and superdislocations, which not only have significantly different critical resolved shear stresses but also differing core structures influencing the deformation, recovery, and recrystallization behavior.[8,9] The complexity of processes during high-temperature deformation is increased by twinning, which is a prominent deformation mode of
-TiAl alloys.[9] Moreover, recrystallization of intermetallic phases is impeded by the low mobility of H.-G. BROKMEIER, Professor, M. OEHRING, Scientist, U. LORENZ, Technician, and F. APPEL, Scientific Group Leader, are with the GKSS Research Centre, Institute for Materials Research, D-21502 Geesthacht, Germany. Contact e-mail: [email protected] H. CLEMENS, Professor, formerly with the GKSS Research Centre, Institute for Materials Research, is with the Department of Physical Metallurgy and Materials Testing, The University of Leoben, A-8700 Leoben, Austria. Manuscript submitted January 28, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A

grain boundaries and the need that the ordered state has to be restored on primary recrystallization.[10,11] As
-TiAl alloys usually are worked in temperature ranges where predominantly the
phase, the  and
phase, or only the disordered hexagonal solid solution  phase are present, not only the texture evolution of different phases, but also the phase transformations on cooling and their effect on texture have to be considered. In this work, the texture development of some current engineering alloys has been investigated on hot working. As hot-working procedures, hot extrusion and sheet rolling were applied, which are relevant from a technological point of view. By comparing different alloying compositions, working conditions, and the differing mechanical