WC–Co cemented carbides build one of the important classes of metal matrix composites. We show in this paper that the use of machine vision methods makes it possible to obtain sufficiently informative statistical data on the topology of the interfaces between tungsten carbide grains (WC) and a cobalt matrix (Co). For the first time, the outlines of the regions of the cobalt binder were chosen as a tool for describing the structure of cemented carbides. Numerical processing of micrographs of cross sections of three WC–Co alloys, which differ in the average grain size, was carried out. The distribution density of the angles in the contours of cobalt “lakes” is bimodal. The peaks close to 110° (so-called outcoming angles) correspond to the contacts between the cobalt binder and the WC/WC grain boundaries. The peaks close to 240° (or incoming angles) correspond to the WC “capes” contacting the cobalt “lakes” and are determined by the angles between facets of WC crystallites. The distribution density of the linear dimensions of the regions of the cobalt binder, approximated with ellipses, were also obtained. The distribution density exponentially decreases with the lengths of the semi-axes of the ellipsoid, approximating the area of the cobalt binder. The possible connection between the obtained data on the shape of cobalt areas and the crack trajectories in cemented carbides is discussed.
Cemented carbides have been known for about a hundred years and are now widely used in mining, civil and road construction, and mechanical engineering. Their improvement requires the development of novel technologies based on fundamentally new approaches. Here the method for microstructure analysis using computer processing with elements of machine learning and artificial intelligence is proposed. It has been applied to the analysis of micrographs obtained by the scanning electron microscopy of the WC-Co cemented carbides. The geometric parameters of the WC / Co interphase boundaries are extracted using mathematical methods for processing digital pictures. This method is applied to the micrographs of three samples with different WC mean grain sizes. It has been found that the distribution of the contact angles of WC / Co interphase boundaries has a pronounced bimodal structure, and the values of the peak angles are practically the same for the samples of the fine-, medium-, and coarse-grain cemented carbide grades. The distributions of the semiaxes for the isolated areas of the cobalt binder are also obtained. The probability of finding a particular value of long and short semiaxis decreases exponentially with increasing semiaxis length. Contrary to the contact angles, the exponents are different for samples with different WC grains sizes. The obtained results are discussed using the ideas of wetting of grain boundaries and faceting-roughening of interphase boundaries.
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