MEASURING & MODELLING THE INSTRUMENTED INDENTATION (NANOINDENTATION) RESPONSE OF COATED SYSTEMS
Résumé
We have been determining the ways in which the mechanical properties of coated systems ｡V including those with very thin (<100nm) coatings - can best be characterised, at the appropriate small spatial scales, using instrumented indentation techniques (IIT). Our approaches have been to critically assess the differing types of sample information available from load-displacement (P-χ) curves, P-χ2 analyses and P-S2 data (where S is the contact stiffness). Parallel insights into the deformation mechanics controlling the contact response have been sought using transmission electron microscopy (TEM), high resolution scanning electron microscopy (HRSEM) and scanning probe microscopy (SPM) to characterise both the detailed appearance of resultant indentations and their underlying deformation structures. Increasingly, many coatings are multilayered and thus there is a need for a modelling approach that can predict the mechanical properties of any proposed multilayer design. Since testing all possible stack sequences and combinations is impossible, we have successfully developed an energy-dissipated-per-unit-volume-of-plastic-zone model to predict the effective hardness, elastic modulus and IIT response in such cases. Such studies are furthering our understanding of the fundamental origins of the mechanical behaviour of coated systems, with particular emphasis on the scale sensitivity of responses and with the purpose of informing systems｡ｦ design. New insights have occurred such as the differing scale-sensitivities of system hardness (Hsys) and elastic modulus (Esys) resulting in there being a critical range of contact scale range over which a maximised elastic contact response can be expected. δ
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