Scale effect in mechanical characterization of WC-Co composites

The study of mechanical response of materials at small length scales has gained importance due to the recent advances in micro- and nano-fabrication as well as testing systems. However, most of the reported work has been dedicated to investigate single-crystals or boundary-containing metallic systems, while much less attention has been paid to composite materials, and in particular those combining soft and hard phases. In this work, a systematic procedure is followed for machining micropillars of diameters ranging from 1 to 4 pm in a WC-Co composite with a WC mean grain size around 1 pm, by means of focused ion beam milling. In-situ uniaxial compression of the micropillars and subsequent field emission scanning electron microscopy inspection were conducted. Clear size effects are evidenced. Smaller test specimens (probe size approaching the mean WC size) exhibit deformation/failure mechanisms observed for WC crystals; while for bigger sample sizes, the mechanical response involves several mechanisms directly linked with the microstructural characteristics of the bulk-like cemented carbide material. On the other hand, independent of micropillar size, carbide-carbide or carbide binder interfaces are found to be preferential sites for nucleation of critical damage events.