Formation of a Surface Carbide Layer During Sintering of Titanium Diboride

Titanium diboride, vacuum sintered in a graphite furnace, can develop a thin TiC surface layer. A mechanism for carbide formation is proposed which takes into account the changing p(CO2)/p(CO) ratio as a function of temperature. At low temperature, TiB2 is oxidized by CO2 to give a surface oxide layer. As the temperature is increased, the reduced p(CO2)/p(CO) ratio allows formation of TiC via a reaction between the oxide layer and CO. The proposed mechanism is supported by thermochemical calculation and microstructural analysis.