Surface effects in crystal plasticity

This paper includes discussion of not only the phenomenology and current mechanistic understanding of manifestations of surface effects in crystal plasticity, but also the application of these phenomena to technology. At the outset, certain aspects of the surface chemistry and physics of various crystalline inorganic solids are examined in order to illustrate that the surfaces of such solids are likely to be structurally, chemically and electronically distinct from the bulk. This is followed by brief discussion of surface effects in uniaxial plastic deformation, the influence of surface films on mechanical properties, chemisorption-induced variations in the plasticity and fracture of metals and nonmetals, and surface effects in embrittlement phenomena. Throughout these discussions emphasis will be placed on areas of controversy and, likewise, an attempt will be made to invoke some of the principles of surface chemistry and physics in describing each topic. The remainder of the paper is intended to demonstrate that our understanding of surface effects in crystal plasticity, imperfect though it may be, has been applied by various investigators with remarkable success to such technological problems as metal cutting, the machining of ceramics, the rapid excavation of hard rock, improvement in the fatigue life of various alloys, and, potentially, even to the control of earthquakes!