Abstract

The talk begins with a brief perspective on the historical background to the subject of Tribology. In regard specifically to the development of wear theories, for many years it was widely believed that the best way to reduce the wear of a surface was to make it harder. This idea was implicit in one of the guiding ‘laws’ of wear (Archard’s Wear Law) which states that wear rate is directly proportional to load and inversely proportional to hardness. In practice, this ‘law’ doesn’t always hold true. What we now know is that (particularly for coated surfaces) both the elastic modulus (E) and the hardness (H) must be considered together when seeking to provide protection. In fact it is the ratio H/E which gives us the best indicator of wear resistance, especially for coatings. In this talk, the reasons for this are discussed and the implications for the development of improved wear-resistant surfaces are outlined, with examples of surfaces which take the optimisation of the H/E ratio as the goal. Examples of coatings which achieve this are discussed, including nanocomposite and nanolayered coatings. Mention is also made of so-called ‘duplex’ coating systems, which combine surface treatments with coatings to gain maximum tribological benefits.