The Interaction of Titanium Boride with Chromium

Abstract

The interaction of titanium diboride with chromium was studied in the temperature range 1200–1950 ºC in vacuum. A solid-phase reaction was established to occur with two-hour holding at the contact boundary up to 1580 ± 20 ºС to form a chromium diboride (Cr₂B) layer 40 µm thick on the chromium side. Above 1580 °C, the interaction process proceeds according to the contact melting mechanism, which is characteristic of eutectic systems. Chromium, a solid solution of titanium in chromium, chromium diboride Cr₂B, and a phase of composition close to ternary boride Cr₂TiB₂ are predominant in the hypoeutectic region of the quasibinary phase diagram. The eutectic forms in the region of 1580 ºC at 14% titanium diboride. The liquid phase formed at 1600 °C wets the diboride surface with a contact angle of ~75º. When temperature increases to 1950 °C, the contact angle decreases to ~10º. The liquid phase interacting with TiB₂ disappears as higher-temperature reaction products are formed. Double (Сr₂B, TiB) and ternary (Cr₂TiB₂) compounds based titanium diboride and chromium lattices show up. The phase composition depends on the ratio of components in the alloy: the amount of reaction products increases with higher titanium diboride content. Considering the eutectic nature of the Cr–TiB₂ quasibinary phase diagram, the small contact angle formed in interaction of titanium boride with the eutectic and the capability of chromium to be uniformly distributed over the charge volume through the vapor phase, chromium is a promising element for activating the sintering process. Based on the studies conducted, a technique for the activated sintering of titanium diboride was developed and allowed its bending strength to be increased by 1.5 to 2 times.