Developments in PVD tribological coatings

Progress in the development and industrial adoption of PVD tribological coa tings over the past two or three decades has been considerable, In particul ar, TIN coatings are in widespread usage in metal-cutting and other tooling applications. However the practical uptake of PVD coatings for components in high-volume industrial sectors (such as automotive) has been relatively slow. There have been many reasons for this. One was that the coatings bein g developed proved to be unsuitable for the low-cost (and relatively soft) substrates which are often used in high-volume applications. The emphasis o n coating development often seemed to be the pursuit of hardness at the exp ense of other useful characteristics. With developments in the understanding of tribological contacts has come th e realisation that hardness (H) may not be the only defining property for w ear resistance. Here we discuss the importance of the elastic modulus (E) a nd the ratio HIE in determining the endurance capability of a surface coati ng, especially its ability to accommodate substrate deflections under load. This is set in the context of new multi-layered and nano-composite coating s which can provide a relatively low E value whilst retaining an adequate l evel of hardness. Furthermore the benefits of pre-treatments and interlayer s to enhance the load support available to the coating from the underlying substrate are described. Overall, the paper presents an insight into how PV D tribological coatings have now been developed to satisfy the requirement of friction and wear contact conditions in many practical applications.