Alloy composition and equilibrium phase diagram for the Sc–Ru–Rh system. V. 930°C isothermal section of the Sc–ScRu–ScRh partial system

Abstract

Microstructure, x-ray diffraction, and electron-microprobe methods have been applied to study an isothermal section at 930°C of the Sc–ScRu–ScRh partial system. As no ternary compounds are formed in the system, the phase equilibria involve intermediate phases based on binary compounds that exist in the bounding Sc–Ru and Sc–Rh systems: Sc₅Ru₃, Sc₂Ru, Sc₁₁Ru₄, Sc₄₄Ru₇, Sc₃Rh, and the δ and η phases (continuous series of solid solutions between the isostructural phases, respectively, ScRu and ScRh (with the CsCl structure type), together with Sc₅₇Ru₁₃ and Sc₅₇Rh₁₃ (Sc₅₇Rh₁₃ structure type)), and a solid solution based on α-scandium. The components of the isothermal section are eight single-phase regions, five three-phase fields (δ+<Sc₅Ru₃>+<Sc₂Ru>, <Sc₂Ru>+<Sc₁₁Ru₄> + η. <Sc₂Ru> + δ+η, >Sc₃Rh> + δ+η, >Sc₄₄Ru₇+<α-Sc>+η, and twelve two-phase regions. There is a difference from the phase equilibria at subsolidus temperatures in that at 930°C there are no equilibria related to the decomposition of the phase based on the compound Sc₂Rh (γ′), and they are replaced by new ones due to the formation of phases based on the compound Sc₄₄Ru₇ (θ) in the solid state.