High-temperature stability of polycrystalline cubic boron nitride cutting tool materials in air

Thermal stability of cubic boron nitride (cBN)–TiC cutting tool material in air was analyzed using TGA and oxidation tests in a muffle furnace within the temperature range 550–1100 °C for a holding time of 60 min. A scanning electron microscope equipped with an energy dispersive X-ray spectroscopy analysis system was particularly used for the characterization of the oxidation scales obtained thereafter.The significance of the results obtained was discussed in terms of oxidation kinetics law, oxidation mechanisms as well as variation of constitution and morphology of the oxidation scale with temperature, keeping focus on the machining context.

► Oxidation of cBN–TiC composites is not passive within 550–1100 °C, obeying a linear rate law.
► Outward diffusion of Ti, Al and C, and inward diffusion of O2 controlled this oxidation.
► Ultimately, the oxidation scale is made of a porous outer layer (TiO2 and Al2O3 sub-layers) and an inner layer.
► Constitution and morphology of the inner layer vary with temperature.
► Formation and evaporation of B2O3 keeps the porosity within the oxidation scale.