Processing of ZrC-Mo cermets for high-temperature applications, Part I: Chemical interactions in the ZrC-Mo system

The chemical compatibility of ZrC and Mo was investigated in carburizing and carbon-free environments at temperatures from 1700 degrees to 2200 degrees C. Heating in the carburizing atmosphere resulted in the complete reaction of Mo with C, while the carbon-free atmosphere resulted in retained metallic phase with a maximum of 13.8 mol% Mo2C formed. The presence of Mo2C was not detected at 2100 degrees C in the carbon-free atmosphere, confirming the existing phase equilibria in the Zr-Mo-C system. Heat treatments in the carbon-free atmosphere also showed liquid formation at 2200 degrees C, as evident from microstructure analysis. Liquid formation was consistent with the interaction between Mo and Mo2C. The liquid was found to comprise at least 7 vol% of the total component, based on a phase diagram for the Mo-C system. The formation of a liquid should allow for the processing of ZrC-Mo cermets by liquid-phase pressureless sintering.