The Bureau of Mines has studied hafnium-iridium phase relations by metallography, thermal analysis, electron-beam microprobe, and x-ray diffraction. Four intermediate phases were identified. Eutectic and eutectoid reactions occur between hafnium and Hf2Ir at 1425 °C and 1375 °C, respectively. Also, eutectics occur between HfIr and HfIr3 at 2085 °C, and between HfIr3 and iridium at 2250 °C. Each of the phases occurs over a range of compositions, except Hf5Ir3 which is nearly stoichiometric.