Influence of stress ratio and WC grain size on fatigue crack growth characteristics of WC-Co cemented carbides
Hirose Yukio; Boo Myung Hwan; Matsuoka Hideaki; Park Young Chul
Abstract: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 6 mm. Fatigue crack growth tests were carried out over a wide range of fatigue crack growth rate covering the threshold stress intensity factor range DK sub t sub h. The fatigue tests were conducted at 10 Hz 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 DK depended on stress ratio R. The crack growth rate plotted in terms of the effective stress intensity factor range DKeff (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. Key Words:fatigue crack growth, WC-Co cemented carbide, stress intensity factor, stress ratio, mean free path, phase transition