Friction in the Presence of Molecular Lubricants and Solid/Hard Coatings

Abstract

Two of the most widely employed approaches for enhancing the lifetime and tribological performance of mechanical devices involve the introduction of lubricants and solid/hard coatings to the interface between two contacting surfaces. These approaches have been employed for centuries, and their design has been widely accomplished through empirical methods. In the last 20 years however, the general trend of device miniaturization and the development of advanced technology applications have placed more stringent demands on the performance of many tribological interfaces. For example, many of the hard-disk storage products now shipped in computers rely upon a single layer of lubricant molecules adsorbed on a submicron-thick layer of amorphous carbon to control the static friction and wear between the read/write head and the disk surface. In other advanced technologies, hard-coating materials are introduced into tribological interfaces that will operate in remote or harsh environments to improve the durability and lifetime of the devices. In the previous examples, the introduction of a thin coating or a change in surface composition dramatically influences the tribological properties and indicates that many tribological interfaces can be understood and described on a molecular scale. This article will review recent progress made in understanding the molecular events associated with tribological phenomena from both experimental and theoretical approaches.In general, advances in experimental studies have been realized through developing a greater sensitivity to the relatively few number of species found within a tribological contact.