Micromechanical characterization of hard phases by means of instrumented indentation and scratch testing

Several hard phases were examined by indentation testing and scratch testing to provide a consistently evaluated database on the mechanical properties and deformation characteristics of hard phases. The analysis of indentations was conducted carefully so that the same method is applicable for hard phases with differing properties. To check whether an influence by the indentation size effect (ISE) is present or not, the Nix-Gao method was used to compute a macroscopic, corrected hardness. Additionally, the possible influence of the surrounding matrix material on the measurements was evaluated. The topography of scratch grooves during scratch tests was determined using a confocal laser scanning microscope. Quantitative information for clearer insights on the deformation characteristics can be acquired with this technique. An indentation size effect was verified to some extent for metallically bonded hard phases. Although the ISE does not have the same magnitude as in metals, it has to be considered if instrumented indentation is used to obtain accurate parameters from hard phases. Matrix effects were also observed and were accounted for. The deformation during indentation and scratch testing showed good correlation between the mechanical parameters and the deformation behavior during scratching. With increasing hardness, the hard phases generally showed more microchipping and deformed elastically to a higher degree. Covalently bonded hard phases yielded the highest hardnesses, and thus the smallest groove areas during scratching, while exhibiting much elastic deformation. Microcracking was observed in scratch grooves of some noncovalent hard phases that could not withstand the stresses underneath the indenter and thus fractured.