Corrosion-induced changes on Hertzian contact damage in cemented carbides

Abstract

In this study, the influence of corrosion on the mechanical response and damage induced under Hertzian indentation is assessed for three cemented carbides with metallic binders of different chemical nature. Corrosion degradation is introduced in a controlled way, before subsequent spherical indentation testing, by immersing specimens in a stirred acidic medium. Results reveal quite strong corrosion effects on indentation stress-strain response and contact damage scenario. Such detrimental influence is found to be dependent on both the ratio between indentation depth and thickness of the corroded layer as well as chemical nature of the binder. In this regard, critical loads for emergence and evolution of specific damage events (i.e. ring and radial cracks, and even specimen failure) are proposed as figures of merit for material selection under the combined action of corrosion and contact loads. Within this context, the hardmetal grade with Co-base binder and addition of Cr is found to be the best option, among the three cemented carbides studied in this investigation. It points out the consideration of the synergic interaction between corrosion resistance and hardness/toughness correlation for microstructural design optimization of hardmetals under service-like conditions. These statements are supported by the relevant corrosion-induced changes also observed, by means of advanced characterization techniques, in terms of deformation/failure micromechanisms at both surface and subsurface levels.