Coatings tribology - contact mechanisms and surface design

The fundamentals of coating tribology are presented by using a generalised holistic approach to the friction and wear mechanisms of coated surfaces in dry sliding contacts. It is based on a classification of the tribological contact process into macromechanical, micromechanical, nanomechanical and tribochemical contact mechanisms, and material transfer. The important influence of thin tribo- and transfer layers formed during the sliding action is shown. Optimal surface design regarding both friction and wear can be achieved by new multilayer techniques which can provide properties such as reduced stresses, improved adhesion to the substrate, more flexible coatings and harder and smoother surfaces. The differences between contact mechanisms in dry, water- and oil-lubricated contacts with coated surfaces is illustrated by experimental results from diamond-like coatings sliding against a steel and an alumina ball. The mechanisms of the formation of dry transfer layers, tribolayers and lubricated boundary and reaction films are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.