Thick Ti/TiN multilayered coatings for abrasive and erosive wear resistance

Plasma-assisted physical vapour deposition (PAPVD) of hard coatings such as TiN is widely employed on cutting and forming tools where a thin coating (i.e. 1–5 μm) is sufficient to control the primary (usually “adhesive”) wear mechanism. Diversification into other application areas, such as components for which abrasive wear resistance is the main requirement, has however been constrained by coating thickness limitations (typically to below 10 μm)—due to debonding caused by the build-up of internal stresses. The hardness and “load-support” mismatch between such coatings and the more widely used metallic (i.e. non-tool steel) substrate materials (both ferrous and non-ferrous) also leads to a requirement to modify coating-substrate interfacial properties and decouple substrate mechanical (and-to some extent-electrochemical) effects from the important coating surface or “near-surface” requirements.

Here we report a technique for interlayering of TiN with titanium to produce a “toughened” composite coating which can be greater than 60 μm thick. By control of layer thickness and interfacial properties, the brittle-fracture failure regime normally associated with TiN on relatively soft substrates can be replaced with a ductile “tearing” mechanism which provides improved performance in three-body abrasive wear tests and airborne-particulate erosion simulation trials. The implications of multilayered and multitreatment coatings in widening the applicability of PAPVD treatments are also discussed.