Microstructural evolution and hardening behaviour of cast and heat-treated Ru−Al and Ru−Al−Ni alloys

Ru−Al alloys with compositions of Ru59Al41, Ru46Al35Ni19, and Ru39Al13Ni48 were prepared via an arc melting technique and subsequent heat treatment at 1450°C for 24 h. Microstructures of the alloys in the as-cast and heat-treated conditions were studied. After heat treatment, cast Ru59Al41 and Ru46Al35Ni19 alloys revealed the presence of needle shaped precipitates with a simultaneous increase in hardness, exhibiting precipitation-hardening behaviour. A morphological instability resulting in the formation of lamellar structures was evident in the heat-treated Ru39Al13Ni48 alloy. Examination indicated that prolonged heat treatment is required to obtain equilibrium phase compositions resulting in a single lamellar structure in this alloy.