Original paper(Vol.46 No.7 pp.726)

Evaluation of fatigue crack growth characteristics of WC-Co cemented carbides

Hirose Yukio; Boo Myung Hwan; Kishi Yoichi; Park Young Chul

Abstract:The fatigue crack growth tests of WC-Co Cemented Carbides were carried out in a wide range of fatigue crack growth rate covering the threshold stress intensity factor range DKth. The effects of the stress ratio, Co volume fraction and the phase transformation of Co on the fatigue crack growth characteristics were investigated on the basis of fracture mechanics and fractography. The crack growth rate was measured using 3 point bending specimens. Crack growth tests were carried out at 10 Hz and the stress ratio R = 0. And 0.5. The main results obtained are as follows;
(1) The Paris rule can be applied between da/dN and DK and it is shown to be da/dN = C (DK)m.
(2) The fractography of the fracture surface, shows that brittle fracture occurs in the Co binder phase at the stress rate R = 0. But ductile fracture occurs in the Co binder phase at R = 0.5.
(3) The relation of da/dN -DKeff/E of WC-Co cemented carbides shows the characteristic in the middle of the other metals and the alumina ceramics.
(4) The Co binder phase undergoes phase transformation by repeated deformation and so it affects the characteristics delicately

Key Words:fatigue crack growth, WC-Co cemented craboed, stress intensity factor, stress ratio, phase transformation