The effect of Mo2C additions on the oxidation resistance of (Ti,W)CN cermets as base material for the production of cutting tools

Abstract

The effect of Mo2C secondary carbide on the oxidation resistance of (Ti0.93W0.07)CN0.3-20%Ni cermet was investigated using DSC-TG, isothermal oxidation, XRD, and SEM/EDS characterisations. Adding Mo2C secondary carbides to (Ti, W)CN cermets is one of the methods used for improving their mechanical properties. However, Mo2C secondary carbides bring a detrimental effect to oxidation resistance. The isothermal oxidation results of the samples at 750 °C possessing 0% and 2% MO2C follow the parabolic law, while in the samples containing 5% and 8% Mo2C, the rate of oxidation and the spallation of the oxide scale increased significantly. The thickness of the oxide layer in the cermet containing 5% of Mo2C increased three times, whereas the mass per unit area of the detached oxides in the 8% Mo2C specimen dramatically increased up to 100 times. The investigations revealed that the increase in the amount of W and Mo on the cermet material, as well as the formation of a multi-zone oxide layer, are the main reasons for oxide phase propagation.