Friction, or the resistance to motion of two bodies in sliding contact, is one of the foremost problems facing the Navy today. For instance, for mechanical components in sliding contact, such as those present inside an engine, low friction is usually desired because friction is ordinarily accompanied by wear that can lead to catastrophic failure of the device.
Traditional ways to reduce friction include judicious selection of materials and liquid lubrication. More recently, solids with good friction and wear characteristics, that can be deposited as coatings, e.g., diamond, are being pressed into service as lubricants. These solids coatings are invaluable in environments where liquid lubrication is not feasible, e.g., at extreme temperatures or in outer space.
Efforts to design low friction coatings a priori have been hampered by the lack of understanding of the atomic-scale mechanisms which govern friction. Recently, new scientific instrumentation, such as the atomic force microscope, has been developed that allows for the study of friction at the atomic scale. Due to recent advances in computer technology, these atomic-scale experiments can also be simulated on computers. These molecular dynamics simulations provide information of unprecedented detail into the processes under investigation because the position of each simulation atom is known as a function of time.
Professor Harrison uses molecular dynamics simulations to investigate the factors which affect the friction between two diamond surfaces in sliding contact. Some variables which are known to affect friction are normal load between the surfaces, environmental conditions, the presence of surface imperfections, adhesion between the surfaces, the formation of debris and transfer films, and hydrocarbon lubrication. Ultimately, knowledge of the way in which all these variables affect friction might play an integral role in the design of coatings with specific friction and wear properties.
"Material contained herein is made available for the purpose of peer review and discussion and does not necessarily reflect the views of the Department of the Navy or the Department of Defense."