Thermal-Induced Wear Mechanisms of Sheet Nacre in Dry Friction

Sheet nacre is a natural biocomposite with a multiscale structure including a mineral phase of calcium carbonate (97 wt.%) and two organic matrices (3 wt.%). The mineral phase is constituted by an arrangement of CaCO3 biocrystal nanograins (ca 40 nm in size) drowned in an "intracrystalline" organic matrix (4 nm thick) in order to form a microsized flat organomineral aragonite platelet. These platelets are themselves surrounded by an "intercrystalline" organic matrix (40 nm thick) building up a very tough materials. This microarchitecture referred to as "bricks and mortar" nacre structure, is mainly studied for the creation of new organic/inorganic hybrid materials. Currently, only little is known about the nacre mechanical behaviour under dynamical loading and more particularly under tribological conditions which involve shocks and thermal effects simultaneously. This paper brings out the thermal-induced damage mechanisms effect on the wear of sheet nacre by the assessment of the thermal component of the friction with a scanning thermal microscope. Results reveal that the mean contact pressure is the main driving force involved in the degradation of the organic constituents. For the lowest mean contact pressure (