The Ir-Rh (Iridium-Rhodium) system

The assessed Rh--Ir equilibrium diagram is shown. The equilibrium phases are liquid, L, and a continuous series of solid solutions (fcc Cu-type) at high temperatures. Below 1335 deg C, two phases--the Rh-rich phase and the Ir-rich phase--separate out, both phases being fcc Cu-type solids. In the review of Pt metal alloys, it was concluded that Ir forms a continuous series of solid solutions with Rh at high temperatures. The possibility of a discontinuity in solid solubility at lower temperatures exists. A recent thermodynamic study indicated a miscibility gap at relatively high temperature. There was an indication of such a phase separation in the hardness measurements. The results of Vickers hardness measurements of "as-cast" Rh--Ir alloys were presented. The hardness of the Rh increased almost continuously (except for a small reduction at approx 11 at.% Ir) up to approx 26.3 at.% Ir and remained almost constant to approx 68.2 at.% Ir. After 68.2 at.% Ir, it again increased linearly. Phase diagrams, Graphs.