The Metal-to-Metal Interface and Its Effect on Adhesion and Friction

Abstract

The interface established by two metal surfaces brought into solid state contact is much more rigidly predetermined than is the interface for the other states of matter contacting themselves or solids. Thus, solid state structural factors at the surface such as orientation, lattice registry, crystal lattice defects, and structure are shown to have an effect on the character of the resulting interface established for two metals in contact. The interfacial structural character affects the adhesion or bonding forces of one solid to another. This in turn influences the forces necessary for tangential displacements of one solid surface relative to the other. Because the nature of the metal-to-metal interface is determined to an extent by the solid surficial layers' surface tools such as LEED, Auger emission spectroscopy and field ion microscopy are used to characterize the solid surfaces prior to contacts and after the establishment of an interface. In addition to the foregoing structural considerations, many of the properties of matter which influence the nature of the interface of the various states of matter with metals are shown to effect the metal-to-metal interface. These include metal surface chemistry and the influence of alloying on surface chemistry and bulk chemical behavior. The nature of the interface, adhesion and friction properties of noble metals, platinum metals, Group IVB metals, and transition metals are considered. Surface chemical activity of the noble and platinum metals are shown to effect metal-to-metal interfaces as does valence bonding in the transition metals. With the Group IVB metals the degree of metallic nature of the elements is shown to effect interfacial behavior. The effect of surface segregation of alloy constituents such as silicon in iron and its influence on the metal-to-metal interface is discussed. In addition, the effect of alloy constituents on changes in bulk properties such as transformations in tin is shown to effect interfacial adhesion and friction behavior.