TEM INVESTIGATIONS OF WC-Co ALLOYS AFTER CREEP EXPERIMENTS

Carbide tungsten cobalt alloys were deformed in compression or in three point bending in a temperature range 1000-1350°C and in a stress domain 30-1000MPa. In these conditions, the stress exponent n of WC-CO alloys is a function of only the cobalt volurnic ratio and tends tow rds n = 1 for pure B carbide. The apparent activation energy is 550 kj mole. T.E.M. investigations on pure carbide deformed at 1450°C show an extensive intragranular deformation. Analysis of these defects have been performed. Moreover an accurate study has shown a different behaviour between coincidence grain boundaries (1 = 2, 4, 13a) and general grain boundaries. These data and macroscopic results allow to propose a model for the deformation of carbide tungsten cobalt composites.