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This study investigates the tribolayer properties at the interface of ceramic/metal (i.e., WC/W) sliding contacts using various experimental approaches and classical atomistic simulations. Experimentally, nanoindentation and micropillar compression tests, as well as adhesion mapping by means of atomic force microscopy, are used to evaluate the strength of tungsten-carbon tribolayers. To capture the influence of environmental conditions, a detailed chemical and structural analysis is performed on the worn surfaces by means of XPS mapping and depth profiling along with transmission electron microscopy of the debris particles. Experimentally, the results indicate a decrease in hardness and modulus of the worn surface compared to the unworn one. Atomistic simulations of nanoindentation on deformed and undeformed specimens are used to probe the strength of the WC tribolayer and despite the fact that the simulations do not include oxygen, the simulations correlate well with the experiments on deformed and undeformed surfaces, where the difference in behavior is attributed to the bonding and structural differences of amorphous and crystalline W-C. Adhesion mapping indicates a decrease in surface adhesion, which based on chemical analysis is attributed to surface passivation.

In this study, polyetheretherketone composites were compounded using a two-screw extruder followed by injection moulding. The effects of multi-fillers on the mechanical properties and crystallization performances were investigated. Differential scanning calorimetry results indicate that the addition of fillers slightly increases the crystallization temperature and crystallinity. Compared to neat polyetheretherketone, the incorporation of inorganic filler leads to a significant improvement in matrix hardness, matrix stiffness and a slight increase in tensile strength. However, the material ductility, the impact strength and the fracture toughness of polyetheretherketone composites decrease. Fractography analyses show that the addition of fillers restraints the ductile deformation of polymers, which is responsible for the reduction of material ductility, impact strength as well as fracture toughness of polyetheretherketone composites.

Time-dependent indentation plasticity experiments have been conducted with single-dislocation resolution on KBr(100) surfaces using atomic force microscopy (AFM) in ultrahigh vacuum. Discontinuous displacements of the the tip (pop-ins) with a typical distance on the order of 1Å or less indicate the nucleation and glide of single dislocations within the sample. Pop-in events were observed to occur repeatedly for as long as 4 min while holding the indentation at constant load. These observations indicate that nucleation of dislocations below the indenting AFM tip is stress assisted and thermally activated. The rate of pop-in events decays with time in a power-law dependence with an exponent of −0.8. The characteristic decay of indentation creep in AFM indentation is much slower than in instrumented nanoindentation for comparable experimental conditions. Closed-loop load controlled and open-loop indentations result in the same pop-in displacement and rate, proving that in AFM-based indentation the influence of instrumental inertia is small compared to most instrumented nanoindentation experiments. A comparison between indentation with sharp silicon tips and with blunter diamond tips demonstrates the importance of the tip radius even at the nanometer length scale; sharper tips activate additional glide systems.