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Dependence of Damage Evolution on Submicro-Micro Characteristics in Co/WC/Diamond Composites

Commercial Co/WC/diamond composites are hard metals and very useful as tool materials. This work studies their damage evolution in dependence of microstructural features. With 90vol.% Co, our material is also a kind of tool material, which is much less studied than the same type of composites with more than 50vol.% WC. The mean size ratio of diamond:WC particles is no less than 10:1. Another special characteristic is that the material behavior can be both ductile and quasi-brittle depending on the portion and local morphology of the diamond. Measurements are performed to achieve real microstructures, the local hardness, the local strain field, the local damage propagation, as well as the macro stress flow behavior. For the finite element (FE) simulations, different methods and techniques are applied. Both real and Poisson Voronoi microstructures are used in 2D and 3D, where residual stresses are taken into account before loading. For submicro-sized WC particles, which are too fine distributed to be meshed with an acceptable number of elements, their strengthening and size effect are taken into consideration through a homogenized matrix (Co-WC). FE results show that the WC phase has a higher mean stress value than the diamond phase, which is proved by the hardness test. The experimental and numerical results are compared on micro and macro scales. For the local strain distribution and the damage development, FE models well predict the reality, even in morphological details. An optimized microstructure should avoid diamond clusters and its local volume concentrations, which easily provoke fatal fracture.