TRIBOLOGICAL PROPERTIES OF THIN HARD COATINGS - DEMANDS AND EVALUATION

Thin hard coatings are currently being used in a large number of tribo logical applications. Some important examples are tools for metal cutt ing and forming, and machine elements like sliding bearings, seals, va lves, etc. The present paper deals with the problems of identifying th e limiting factors in given tribological applications of coating compo sites, and how to experimentally determine their tribological response , with special attention given to wear. As a means for coating develop ment, the intricate relations between coating deposition parameters an d the tribological response of the coated composite are indicated by a flow chart of relevant coating and substrate properties. It is demons trated how the general characteristics (topography, composition, micro structure, etc.) and fundamental properties (chemical, thermal, mechan ical, etc.) of coating and substrate combine to generate the tribologi cal properties (resistance against abrasion, erosion, sliding wear, et c.), which, given the tribological loading, determines the tribologica l response in terms of friction and wear. A number of different test m ethods for tribological evaluation of coating composites are presented together with illustrative examples. The tests range from four-point bending for evaluating coating fracture strength, to designated tribol ogical tests to determine the resistance against abrasion, particle er osion, and sliding wear. (C) 1997 Elsevier Science S.A.