THE HF-OS PHASE-DIAGRAM

Phase ratios in Hf-Os alloys and phase transformations occurring in th em were studied. The Hf-Os phase diagram throughout the concentration limits and in the 1000-2800 degrees C range was plotted. The system fo rms three intermediate phases based on HfOs2 compounds, Laves phases w ith MgZn2(lambda) type structure, HfOs with CsCl(delta) type structure and HfOs17 with complex rhombic structure (gamma). Hf2Os and Hf71Os29 compounds which availability is reported in literature were not ident ified. The lambda- and delta-phases are melted congruently and the gam ma-phase is melted incongruently (gamma-->L+delta at 1620 degrees C), L-->lambda+Os> (2525 degrees C), L-->lambda+delta(2550 degrees C), L-- >lozenge beta-Hf+gamma (1600 degrees C), <beta-Hf> + <alpha-Hf> = gamm a(1220 degrees C) reactions take place in the system.