1982 Volume 48 Issue 7 Pages 899-905
Surface integrity, which is defined by the overall qualities of solid surface from topological, mechanical, physical, chemical and metallurgical standpoints, is generally influenced by the surface processings. In this study, the effect of the surface properties of WC-Co cemented carbide tools, which are determined by the grain size of the tool grinding diamond wheel, on their brittle fracture is investigated experimentally, and the fractographical analysis is done in order to clarify the mechanism of fatigue type of brittle fracture of cemented carbide subjected to the cyclic impact tests and the cutting tests. It is found by the intermittent turning test and the cyclic impact test that the tool life due to brittle fracture decreases with a decrease in the diamond grain size of the grinding wheel. The X-ray diffraction analysis shows that compressive residual stress is produced within the WC grains of the surface layer by grinding and the binder phase is plastically deformed or work-hardened. Both the absolute values of residual stress and the degree of work-hardening in the surface layer increase with an increase in the diamond grain size. The successive microscopic observation of cemented carbides with the progress of the cyclic impact tests reveals that plastic deformation in the binder phase is likely to initiate microcracks mostly in the grain boundaries. The initiation of microcracks is suppressed by work-hardening, and the propagation of microcracks is decelerated by compressive residual stress.
