Solidus Surface of the Hf–Rh–Ir System

Phase equilibria in the Hf–Rh–Ir system at subsolidus temperatures (about 20-50 °C below solidus temperatures) were studied using optical microscopy, scanning electron microscopy, electron probe microanalysis, differential thermal analysis, x-ray diffraction and solidus temperature measurements (Pirani-Althertum technique). For the first time it was established that the solid solution based on βHf, continuous series of solid solutions between isostructural (Cu-type) components iridium and rhodium, isostructural compounds Hf₂Rh and Hf₂Ir (Ti₂Ni-type), high-temperature modifications of HfRh and HfIr (CsCl-type), HfRh₃ and HfIr₃ (AuCu₃-type), as well as solid solutions based on the compounds Hf₅Ir₃ and Hf₃Rh₅ take part in phase equilibria. Solidus surface of this system is formed by seven single-phase surfaces corresponding to solid solutions based on components and above-mentioned compounds, eight tie-line surfaces limiting the two-phase volumes, and two isothermal planes corresponding to invariant four-phase equilibria with participation of the liquid phase (at 1958 and 1655 °C).