PHASE DIAGRAMS HAFNIUM-VANADIUM AND HAFNIUM-CHROMIUM

The binary systems hafnium-vanadium and hafnium-chromium were determined by means of X-ray, melting point, DTA, and metallographic techniques. In the hafnium-vanadium system, β-Hf dissolves up to 23.5 at.% V (1456 °C), whereas the solid-solubility in α-Hf is less than 2 at.%. Vanadium dissolves up to 4 at.% hafnium. The β-Hf solid solution disproportionates in a rapid eutectic reaction at 1190 ° ± 25 °C and 19 at.% into the α-modification and HfV2. The only intermediate compound, HfV2, has a f.c.c., c15 type structure (a = 7·398 A ̊ at the hafnium-rich, a = 7·386 A ̊ at the vanadium-rich homogeneity limit at 1450 °C), and melts congruently at 1550 ° ± 10 °C at the stoichiometric composition. Eutectic equilibria are formed between HfV2 and β-Hf at 43 at.% V and 1456 °C, and between HfV2 and V at 69 at.% V and 1520 °C. The hafnium-chromium system contains one intermediate phase, HfCr2, with a hexagonal, c14-type of structure. The phase extends from approximately 64 at.% Cr (a = 5.090 A ̊; c = 8.25 A ̊), to ~ 67 at.% Cr (a = 5.056 A ̊; c = 8.21 A ̊) at 1500 °C and melts congruently at 1870 ° ± 15 ° at the stoichiometric composition. β-hafnium takes a maximum of 13 at.% Cr into solid solution (1170 °C), and the β-solid solution containing 11.5 at.% Cr decomposes in a rapid eutectoid reaction at 1355 ° ± 15 °C into α-hafnium and HfCr2. The maximum solubilities in α-Hf and in Cr are less than 2 at.%. Eutectic equilibria are formed between the β-Hf phase and HfCr2 at 41 at.% Cr and 1510 ° ± 8 °C, and between HfCr2 and Cr at 87 at.% and 1690 ° ± 15 °C. © 1968.