KINETICS OF WC-CO OXIDATION ACCOMPANIED BY SWELLING

The oxidation behaviour of WC-Co sintered carbides with 3-5 mu m grain size of WC and 6-15 vol.% of cobalt have been studied in air in the temperature range 650-800 degrees C. The intensive swelling of up to 350% of initial specimen size and linear kinetics of the growth of the porous WO3 layer were observed during the oxidation. The final shape of the specimen after oxidation was dependent on its initial shape. The apparent activation energy of the dimension and weight gain kinetics were within the range 32-67 kJ mol(-1) and the process was proposed to be controlled by the reaction at the interface. The oxidation rates and swelling coefficients increased when the mean size of WC grains was decreased and cobalt content increased. The possible model of WC-Co alloys' oxidation and swelling was proposed for the observed shape development and kinetics of oxidation.