Liquidus Surface and Melting Diagram of the Hf-Rh-Ir System

The liquidus surface, melting diagram (superposition of the liquidus and solidus surfaces) and Scheil diagram of the Hf-Rh-Ir system are presented for the first time based on results of the study of as-cast alloys using optical microscopy, scanning electron microscopy, electron probe microanalysis, differential thermal analysis and x-ray diffraction techniques taking into account the constitution of the solidus surface. In the Hf-Rh-Ir system a continuous series of solid solutions between isostructural compounds Hf₂Rh and Hf₂Ir (with the Ti₂Ni-type structure), high-temperature modifications of compounds HfRh and HfIr (CsCl-type), HfRh₃ and HfIr₃ (AuCu₃-type), iridium and rhodium (Cu-type), as well as solid solutions based on βHf, compounds Hf₅Ir₃ and Hf₃Rh₅ take part in phase equilibria. Two invariant four-phase reactions (peritectic at 1958 °C and transition at 1655 °C) involving liquid and corresponding three-phase equilibria take place in this system.