In-Situ Observation and Modelling of Friction and Wear Processes at the Nanoscale

Northwestern University, Evanston IL

Investigators

Abstract

Friction is a pervasive phenomenon; by some estimates it represents between 2 and 6 percent of the GDP of developed countries, and in passenger cars, one-third of the fuel energy is used to overcome friction in the engine, transmission, tires, and brakes. Beyond energy, friction and wear are important for orthopedic devices. A variety of conditions, most notably osteoarthritis, may result in need of a patient for prosthetic joint implants of the hips and knees. Every year, as the baby boom generation ages and patients live longer and more active lives the demand for hip replacements rises and in the US is expected to grow 174 percent from 2005 to 572,000 by 2030. This project targets understanding some of the basic processes in friction and wear of materials used in both technological and biomedical applications. An improved understanding of these processes may be pivotal to design of better performing systems in commercial applications as well as longer lasting implant devices. This project will also assist in the exposure of underrepresented groups to research, outreach activities to high-schools and enhance the Infrastructure for Research and Education through workshops and science outreach. This project is a joint experimental and theoretical approach to establish some of the basic materials science of weak interfaces and selvedge layer deformation important in tribology. The experimental component exploits an in-situ holder which allows the observation of samples during tribologically relevant experiments in a transmission electron microscope, monitoring nanoscale structural and chemical changes in real time. In-situ observations of tribological processes provide unique information about the fundamental processes taking place which can at best only be inferred from other experiments. There already have been cases where what takes place has led to revision of accepted views of tribological processes at the nanoscale, and there almost certainly will be more from the work. The theoretical component will be to apply some of the existing materials science models which are known to work well for strong interfaces to the case of weak interfaces, and from this attempt to extract general models, synergistic with the experiments. The global strategy of this project is to look at the nanoscale processes taking place during sliding as a materials science problem in a bottom-up approach. Some of the specific targets of the work involve in-situ observations of the formation of tribolayers, understanding the deformation in the selvedge layer for ductile and non-ductile materials, in-situ observations of tribochemical changes coupled primarily with dislocation-based continuum modelling.