Measuring the fracture toughness of single WC grains of cemented carbides by means of microcantilever bending and micropillar splitting

Abstract

The main goal of this work is to obtain a reliable value of the fracture toughness of single grains of tungsten carbide (WC). It is attempted by testing microcantilever and micropillar samples shaped out, by means of focused ion beam milling, of individual WC particles embedded within a WC-Co cemented carbide grade. Experimental testing included the use of a nanoindenter for inducing microcantilever bending and micropillar splitting, as well as sampling WC grains with basal and prismatic orientations. Experimental results are compared with those previously assessed through implementation of the indentation microfracture technique. Bending of notched microcantilevers yielded more consistent results than those measured out of micropillar splitting tests. In this regard, the average value of fracture toughness for single WC grains, within the two-phase interpenetrated network existing in cemented carbides, is found to be 5.6 ± 0.8 MPa·m1/2. Such a relatively high value – coherent with local plastic features evidenced in nanoindentation imprints - is in satisfactory agreement with results indirectly estimated from other macromechanical tests.