A constituional diagram of the system VCsub(0.88)-HfCsub(0.98)-(MoC)

The system VCsub(0.88-HfCsub(0.98)-''MoC'' was investigated by means of melting point, differential-themoanalytical, x-ray diffraction and metallographic techniques on hot pressed and heat treated as well as melted alloy specimens and a constitutional diagram from 1500 deg C through the melting range established. The small miscibility gap within the HfC-''MoC'' system (Tsub(c) =1630 deg C) interacts at lower temperatures with the solvus in a monotectoid-like reaction at approximately 1575 deg C. Additions of VC to the HfC-''MoC'' solid solution gradually increase its critical temperature. Solid state phase behavior and melting behavior was established within the isopleths VCsub(0.88)-''MoC'' as well as within (Vsub(0.5)Hfsub(0.5))C-''MoC'' and (Vsub(0.75)Hfsub(0.25))C-(Hfsub(0.75)Mosub(0.25))C. Phase equilibria within VCsub(0.88)-HfC-''MoC'' are characterized by an extremely large miscibility gap at 1500 deg C connecting the VC-HfC and HfC-MoC systems. Originating at the VC-HfC binary an eutectic through proceeds into the VC-HfC-Mo ternary with rising temperatures, connecting the maximum critical point of the disappearing miscibility gap [(Vsub(0.31)Hfsub(0.49)Mosub(0.20)C] by a limiting tie line (2750 +- 20 deg C). Isothermal sections have been calculated assuming regular solutions. (author)