The tribology of surface coatings, particularly ceramics

The development of the chemical vapour deposition and plasma-assisted vapour deposition processes has produced major improvements in the performance of tribological coatings. Such processes produce thin, of the order of a few micrometres, highly adhered coatings for engineering components for improved wear and corrosion resistance. The paper shows the effect of substrate and film materials on trihological performance. With such thinfilms it is shown that surfacefinish is of major importance and particular emphasis is given to the behaviour of ceramic films. The paper concentrates on the general physical principles governing the tribological behaviour of thin solid j lms. It is hoped that this presentation will stimulate interest in further extensions of knowledge and encourage a wider application of coatings in industrial service. NOTATION Hertzian radius of contact Hertzian radius of contact of bulk coating material non-dimensional limit of asperity heights separation of surfaces depth wear elastic modulus equivalent elastic modulus non-dimensional separation = d/o hardness effective hardness distance of sliding nominal pressure non-dimensional pressure = P/H fatigue law exponent radius non-dimensional asperity height = z / o coating thickness volume wear load asperity height asperity radius normal approach of asperities hysteresis loss coefficient strain asperity density coefficient of rolling resistance coefficient of sliding friction Poisson ratio standard deviation of asperity height probability distribution asperity height probability distribution non-dimensional asperity height probability dis-tribution plasticity index = (E ’ /H)J(a /P)