The ternary system: hafnium-silicon-uranium

Phase equilibria in the system Hf-Si-U were established at 1000 °C by optical microscopy, EMPA and X-ray diffraction. No ternary compound was observed; however, at 1000 °C, a rather wide solid solution extends from binary Hf5Si4 into the ternary system, UxHf5−xSi4, 0 ≤ x ≤ 1.3. In as-cast alloys, the solid solution extends up to x = 1.6. The crystal structure of the solid solution was characterised by X-ray powder-data refinement and found to be isotypic with the Zr5Si4-type for the entire homogeneity region. X-ray intensity data were consistent with a random substitution, Hf/U, in one of the Hf-atom sites of Hf5Si4. Mutual solubility of U-silicides and Hf-silicides was found to be below about 0.6 at.% except for about 1.6 at.% Hf in U3Si2 in alloys annealed at 1000 °C. The Hf-U-rich part of the diagram was also investigated at 850 °C establishing the tie-lines to the low temperature compounds U3Si and Hf2Si.