Legierungsverhalten von HfB 2 mit uran- und übergangsmetalldiboriden

Abstract

Phase boundaries in the ternary hafnium-uranium-boron system are delineated for the 1100°C section on the basis of X-ray examination in the temperature range 1100–1700°C. The ternary equilibria are: HfB 2UB 12UB 4; HfB 2UB 4UB 2; HfB 2UB 2(U, Hf) and HfB 2HfB(U, Hf), where the brackets represent saturated solid solutions. The mutual solubility of the diborides of the transition metals titanium, zirconium and hafnium, and uranium diboride is slight because of the considerable disparity in c a . The formation of mixed crystals between hafnium diboride and the other transition metal diborides, and the mutual solubility of all these diborides, can be understood in terms of the size differences of the transition metal atoms. All binary systems with radius differences <14% have complete mutual solubility. The systems HfB 2MoB 2 and ZrB 2MoB 2, for which the radius difference = 14%, have partial and complete mutual solubility, respectively. All systems with a greater radius difference have a solubility gap.