Abstract
The influence of cobalt content on the fatigue strength and fatigue phenomena in tungsten carbide-cobalt alloys were investigated. The test was done at 8000 rpm by using a rotating beam fatigue machine.The results obtained are as follows:(1) The S-N curves in WC-Co alloys do not show flat portions which are observed in the case of iron and steel materials. Taking N=108 rpm for the fatigue limit, the fatigue strength increases with cobalt contents. There is a linear relation between fatigue strength and tensile strength.(2) Enlarged pictures of the fatigue fracture surface indicate that the crack runs emissively, with the stress concentration source as the central figure. Electromicrographs of the crack source neighborhood exihibit a kind of fusional structure. This fusional part may be due to the excessive stress concentration.(3) According to the results of X-ray diffraction, the binder phase transforms from γ Co (fcc) to ε Co (hcp) by fatigue and it’s ε content increases with fatigue degree.(4) The coercive force increases with increasing fatigue and stress.
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