Formation of eutectic RuAl/Ru nanocomposite by mechanical alloying and subsequent annealing
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Formation of eutectic RuAl/Ru nanocomposite by mechanical alloying and subsequent annealing K.W. Liua) and F. Mu¨cklich Department of Materials Science, Functional Materials, Building 22, Saarland University, P.O. Box 151150, Saarbru¨cken, D-66041, Germany
R. Birringer Department of Physics, Building 43, Saarland University, P.O. Box 151150, Saarbru¨cken, D-66041, Germany (Received 16 October 2000; accepted 25 May 2001)
No abrupt reaction was observed during mechanical alloying (MA) of Ru and Al powder mixtures with an eutectic composition (Ru70 Al30). As-milled powders constitute mainly a Ru(Al) solid solution and/or mixture (matrix), and a very small quantity of RuAl. The complete reaction between Ru and Al during MA was speculated to be hampered by excess Ru in Ru70 Al30. No exothermic heat release was detected in differential scanning calorimetry for as-milled powders. Precipitation of RuAl from as-milled Ru(Al) matrix was observed after annealing at various temperatures. The phase fraction of Ru and RuAl reaches an approximately equilibrium value after annealing at 1173 K.
The B2-structured intermetallic compound RuAl is characterized by a high melting point (about 2323 K), good room-temperature toughness, high temperature strength, and high oxidation and corrosion resistance.1,2 RuAl-based alloys have been considered as potential materials for high-temperature applications in aggressive environments.3 Eutectic systems provide some potential tailoring routes for high-temperature intermetallics because they are, in general, thermodynamically stable and possess inherent interphase compatibility at elevated temperatures. In addition, the potential capacity for combining a ductile phase in a brittle matrix in certain eutectic systems makes it more meaningful to improve the toughness of the materials.4 The high eutectic point (2173 K) in the binary Ru–Al system with a composition of Ru70 Al30 (at.%) provides a basis for the application of such a material at elevated temperatures.5 The notorious brittle nature of the element Ru6 and the exceptionally ductile nature of RuAl1,2 constitute a suitable combination of brittle and ductile alloy systems.7 The RuAl/Ru eutectic alloy has been found to possess a tolerable ductility and to exhibit a much higher strength than RuAl-based
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 9, Sep 2001
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alloys.7 Due to the high melting point and the great difference in melting points of the component elements, RuAl-based materials are difficult to manufacture by conventional processes.3 Eutectic Ru/RuAl alloys prepared by the casting route, for instance, result unavoidably in a coarse primary phase and fine eutectic phases. The great difference in the colony size of both coarse and fine phases would somehow deteriorate the properties of the material by inhomogeneous deformations between the two regions.7 This problem could be diminished by refining the primary phas
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