High Temperature FeB-type Phases in the Systems Ta-{Ti, Zr, Hf}-B

Novel FeB-type phases have been evaluated in the systems Ta-{Ti, Zr, Hf}-B either from as cast or arc treated samples by x-ray powder and single crystal diffraction as well as electron probe microanalysis. In each of the three systems the formation of the FeB-type phase suggests a high temperature stabilization of a binary group IV metal monoboride with FeB-type. This holds true for Ti and Hf, while for Zr the single crystal study of (Ta,Zr)B proves that it is a true ternary phase, as no stable monoboride exists in the binary Zr-B system. EPMA analyses reveal that the FeB-type phases Ta{Ti, Zr, Hf} B are formed by substitution of Ta in TaB by rather small amounts of group IV elements (similar to 3 at.% of Zr, similar to 7 at.% Hf, and similar to 10 at.% Ti).