LOW-CYCLE FATIGUE OF WC-CO SINTERED CARBI DES

Cyclic stress-strain response, fatigue life and fatigue fracture were studied under symmetrical push-pull loading in WC-9wt.%Co hardmetal. T he microstructure of the two-phase material was analysed. Specimens ha d cylindrical central part with a gauge length of 12 mm and diameter o f 6 mm and flat ends for hydraulic gripping. A constant load amplitude and a constant load rate of 56.5 kN s-1 were maintained. The Young's tensile modulus and the effective moduli in compression and in tension unloading were evaluated. Plastic strain amplitude represents only 1 to 2% of the total strain amplitude. After early rapid hardening sinte red carbides exhibit saturation during the whole life. The basic cycli c stress-strain curve (CSSC) is in good agreement with the CSSC determ ined by the multiple step test procedure. Within the stress amplitude interval of 500 to 1250 MPa the CSSC was fitted by a power law. Fatigu e life curves are presented in the form of stress amplitude versus lif e and saturated plastic strain amplitude vs. life. Defects in the stru cture are responsible for the appreciable scatter of the experimental data. The macroscopic defects are the sites of fatigue crack initiatio n.