Thermomechanical Treatment of a Fe 3 Al alloy
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Thermomechanical Treatment of a Fe3Al alloy Joachim Konrad1,2, Stefan Zaefferer2, André Schneider1, Georg Frommeyer1, Dierk Raabe2 1 Materials Technology, 2Microstructure Physics and Metal Forming Max-Planck-Institut fuer Eisenforschung GmbH Max-Planck-Str.1 40237 Duesseldorf ABSTRACT A binary Fe3Al alloy is investigated with respect to hot and warm rolling behavior and microstructural as well as microtextural modifications. Rolling has been performed in the A2 and B2 order regimes. The differences in microstructure are investigated. The performed texture analysis reveals the differences in hot and warm rolling textures depending on the hot rolling temperature. On the basis of microtexture investigations by means of electron backscatter diffraction (EBSD) differences concerning orientation gradients and sub-grain structures are found. A model of combined order-related and non-order related effects is proposed explaining the observed material behavior. The results are used for process modification. INTRODUCTION Fe3Al-based alloys are regarded as promising for high temperature applications in corrosive atmospheres. Generally Fe3Al shows higher strength compared to disordered Fe-Al alloys and good corrosion resistance in oxidizing and sulphidising atmospheres. At room temperature the material has D03 crystal structure, at temperatures of 546 °C (for the binary alloy Fe 26at.%Al, [1]) it transforms into a B2 structure and at 829 °C into a disordered A2 structure. The longrange order at low temperatures leads to a lack of room temperature ductility which is attributed to the low mobility of superdislocations present in the D03-ordered state and the difficulty of cross-slip due to the generation of anti-phase boundaries [2]. Thermomechanical treatment of Fe3Al-based alloys is regarded as important method to overcome their intrinsic brittleness. Sun et al [3] introduced a concept of thermomechanical treatment in the temperature range of the B2ordered phase. The process, consisting of hot and warm rolling steps and heat treatments below the recrystallization temperature, leads to an improvement of room temperature ductility [4]. This increased ductility is considered to be based on residual single fold dislocations created during hot deformation [4] and on strain induced disordering [5]. McKamey[6], in contrast, attributed the increased ductility of recovered (but not recrystallized) material to the reduction of environmental embrittlement - an extrinsic effect attributed to reactions of the environmental water vapor with the aluminum atoms - due to the elongated grain structure. Finally, the crystallographic texture of the recovered material may also have an influence on the ductility [4]. In the project on which we report here it is investigated whether a thermomechanical treatment in the A2 region (i.e. above 829 °C [1]) where the material is completely disordered [7] could further improve the warm rolling behavior as well as the mechanical properties at room temperature. At these temperatures thermally activate
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