Synthesis and characterization of single-phase B2 structured RuAl intermetallic compound by powder metallurgy

The unusual combination of high temperature strength and room-temperature ductility in addition to excellent oxidation resistance makes RuAl intermetallic compound attractive for high-temperature applications. Difficulties inherent in the manufacture of RuAI by melt processing can be circumvented by powder metallurgy. In this study, Single-phase RuAI was synthesized from elemental powders by reactive sintering and reactive hot pressing. Both processes involve a self-propagating exothermic reaction between the constituent powders to form an intermetallic compound. It was shown that particle size ratio, initial composition, and pressure strongly affect the reaction rnechanism, structure, and density of the final material. Without pressure, reactive sintered products had a relative density up to 81% of the theoretical value and were mainly composed of RuAI with uniformly distributed large pores. Green density has also an effect on densification. An initial excess of aluminum of 1.5 at.% over the stoichiometric composition is necessary in order to compensate for aluminum loss during reactive sintering in vacuum. The application of pressure before the self-ignition of the green compact leads to the formation of a multiphase structure. Molar volume effect between reactants and products, and heat transfer from the specimen after the reaction are assumed to be the main reasons for the formation of the multi phase structure. An extended homogenization treatment was necessary to drive the reaction to completion and to obtain single-phase RuAI. In addition, homogenization resulted in a relatively high-densified product (relative density as much as 94.4%).