Recent advances in the study of high-temperature behaviour of non-stoichiometric TaC _x , HfC _x and ZrC _x carbides in the domain of their congruent melting point

The parameters of the solidus and liquidus phase transitions for TaCx, HfCx and ZrCx are studied using a laser heating technique. A special emphasis is given to the accurate measurement of temperature and determination of spectral emissivity in course of the laser heating using advanced multichannel pyrometry. The phase transitions corresponding to the solidus and the liquidus are determined by means of the laser-probe reflectometry and by the peculiarities in the behaviour of spectral emissivity in the vicinity of the phase transitions and by the high-speed video recording of the melt formation and freezing. New data on solidus and liquidus parameters for the Zr–C system in the homogeneity domain (solid solution) are presented. The temperatures of congruent melting of super-refractory carbides TaC and HfC are determined along with the data on their solidus and liquidus lines close to the composition of congruent melting.