Influence of Stress Ratio and WC Grain Size on Fatigue Crack Growth Characteristics of WC-Co Cemented Carbides.

In order to study the influence of stress ratio and WC grain size, the characteristics of fatigue crack growth were investigated in WC-22wt.% Co cemented carbides with two different grain sizes of 3 and 6μm. Fatigue crack growth tests were carried out over a wide range of fatigue crack growth rate covering the threshold stress intensity factor range ΔKth. The fatigue tests were conducted at 10Hz and two stress ratios R=0.1 and 0.5 in laboratory air at room temperature using the 3-point bending specimens. It was found that the crack growth rate da/dN against the stress intensity factor range ΔK depended on stress ratio R. The crack growth rate plotted in terms of the effective stress intensity factor range ΔKeff (after allowing for crack closure) still exhibited the effect of microstructure. Fractographic examination revealed brittle fracture at R=0.1 and ductile fracture at R=0.5 in Co binder phase. The amount of Co phase transformation was closely related to the fatigue crack growth characteristics.