Experimental investigation and thermodynamic modeling of Hf–Si–B system

Microstructure and phase equilibria of selected alloys of Hf–Si–B system have been studied in annealed conditions mainly by means of X-ray powder diffraction with aid of scanning electron microscope analysis. Compound Hf5Si3B0.2 taking hexagonal structure (space group P63/mcm), was confirmed with each unit cell containing two formulas and having lattice parameters a = 7.8557(1) Å and c = 5.52622(1) Å. Its crystal structure is made up of regular BHf6 and HfSi6 octahedra connected each other along <0 0 1 −1> direction by sharing common faces. This features a three-dimensional framework which is similar to that of analogue Mn5Si3 structure. Besides, a thermodynamic description of Hf–Si–B system was developed based on its constituent binary systems and ternary experimental data from literatures and this work. Isothermal sections at 1273 K and 1573 K were calculated from our newly assessed thermodynamic description with comparison of experimental data.