Cold-Deformation and Annealing of equiaxed L1o-ordered FePd Intermetallics
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0980-II03-06
Cold-Deformation and Annealing of Equiaxed L1o-Ordered FePd Intermetallics Anirudha Desphande1 and Jorg Wiezorek2 1 Dept. of Materials Science and Engineering, University of Pittsburgh, GE-lighting technology, Willoughby, OH, 44094 2 Dept. of Materials Science and Engineering, University of Pittsburgh, 848 Benedum Hall, Pittsburgh, PA, 15261 ABSTRACT The L10 ordering equiatomic intermetallic FePd has been used as a model system for the investigation of the evolution of microstructure and properties during annealing at temperatures below the ordering temperature after cold deformation. The two different routes for the preparation of equiaxed L10 FePd polycrystals, annealing after cold deformation in the disordered FCC state or after cold deformation in the ordered state, produce similar grain size distributions, differ in the transformation kinetics and in the sequence of texture evolution during the post-cold-deformation annealing. Cold deformed L10 FePd progresses through the classic stages of annealing known from studies of disordered elemental metals and alloys based on them. The reduced long range order parameter of the ‘mechanically disordered’ FePd is recovered in the early stages of annealing and both the recrystallization and the grain growth stages are quite sluggish, presumably because of the slow diffusion processes in the L10 lattice. INTRODUCTION Annealing of cold-deformed ordered intermetallics is of technological importance and basic scientific interest, especially for systems that undergo an order-disorder transition in the solidstate [1-4]. While the ordered state has little effect on the recrystallization behavior during annealing of B2-ordering intermetallics relative to that of the disordered concentrated solidsolution, apparent retardation or complete suppression of recrystallization has been reported for L10- and L12-ordering intermetallics [1,2]. Most previous reports used cold-deformation in the disordered state followed by isothermal annealing at temperature below and above the critical ordering temperature and were limited due to the lack of ductility of polycrystals in the ordered state [3-6]. The mechanistic origins for the reported apparent retardation of the recrystallization kinetics for polycrystalline L10- and L12-ordering intermetallics remain to be elucidated [1-6]. The FePd system offers model alloys to investigate systematically the annealing behavior of both L10- and L12-ordering intermetallics [7]. For compositions of about 50 atomic % Pd and 75atomic % Pd concentrated FCC solid solutions exist, which upon cooling below composition dependent temperatures, T0, form an L10-phase FePd (T0≈923K for Fe50Pd50) and an L12-phase FePd3 (T0≈990K for Fe25Pd75). Conveniently, the ordered phases exhibit considerable ductility, at least under compressive and rolling constraint [7]. Here we focus on the study of the L10ordering intermetallic. Two different thermo-mechanical routes exist to establish polycrystalline microstructures with equiaxed morphology in the L10 ordering FeP
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