| The present study utilizes contact mechanics techniques to address several critical aspects of micro/nanotribology. An emphasis is placed on scale, structure and environmental effects. Scale effects refer to the earliest stages of plastic deformation where continuum laws are no longer applicable. Structure effects involve complex relationships between microstructure and mechanical behavior. Environmental effects are manifested in changes of deformation and fracture under exposure to aggressive environments.; Scale effect studies involved evaluation of the plasticity initiation in MgO and W single crystal materials utilizing AE monitored nanoindentation. Newly developed AE sensors incorporated into indenter tips (Hysitron, Inc.) provided greatly enhanced resolution and sensitivity to localized plasticity and fracture events at submicron indentation depths. Based on the analysis of indentation curves and AE waveforms associated with the yield initiation events, new insights into yield point phenomenon were gained.; Microstructure effects were addressed with a newly developed mechanical property evaluation method. With this method, mechanical properties of brittle porous nanocrystalline SiC film on Mo substrate were derived from the complex indentation response involving densification and fracture.; Evaluation of environmental effects involved deformation and fracture of bulk materials and interfaces. Indentation curve analysis combined with the AFM imaging of tested areas provided quantitative measures of hydrogen induced hardening and plastic strain localization in 316 stainless steel. A newly developed indentation based experimental procedure allowed quantitative evaluation of hydrogen effects for Cu/SiO2 interfaces with and without several nm thick Ti interlayers. Up to 50% reduction of the apparent practical work of adhesion was observed in Cu/Ti/SiO 2 films as revealed by indentation testing immediately after hydrogen charging. Finally, a novel approach for the in-situ evaluation of passive film stresses and growth kinetics was developed. It was demonstrated that the evolution of passive films and the stress acting in these films can be followed using a depth sensing continuous indentation into surfaces under potentiostatic control. Based on the recorded indenter tip displacement, time-dependent passive film thickness and stress can be determined with the proposed theoretical model. |
