COMPONENT-INTERACTION MECHANISM IN THE QUASIBINARY HfB₂–Cr SYSTEM

Abstract

The interaction of hafnium boride and chromium in the HfB₂–Cr system is studied. At temperatures up to 1650 ± 30 °С, the process is found to occur as a solid-phase reaction to form chromium boride (Cr₂B) on the chromium side of the HfB₂–Cr system. The diffusion of boron from hafnium diboride to chromium is the control link in this process. At 1650 ± 30 °С, a liquid phase of eutectic composition with a contact angle on hafnium diboride of 20° shows up in the reaction zone. The interaction turns into the dissolution of each element of the contacting couple in the eutectic, followed by leveling their concentrations though liquid-phase diffusion. Given the eutectic nature of the quasibinary HfB₂–Cr phase diagram, a small contact angle formed by the eutectic on hafnium diboride, decreasing with higher temperature, and high chromium vapor pressure, allowing chromium to be evenly distributed over the entire charge through the vapor phase, chromium seems to be a promising material to be added to activate the sintering of hafnium diboride.