ABSTRACT
Alumina, as a bulk material, exhibits high oxidation resistance, high chemical stability, high hardness, and good wear resistance, which makes it desirable for use in applications where these properties are indispensable for a successful performance in service. However, in a large number of applications, the use of this material is strongly but its low toughness and poor machinability. This has led to the production of alumina coatings where the 'good' properties can be exploited whilst the 'poor ones' can be avoided by the use of tougher substrate materials to be coated, for example steel. Using different deposition techniques and/or different deposition conditions, it is possible to adapt the alumina-coated component to a large spectrum of applications. Nevertheless, the production of these coatings, as in the case of other coatings, has faced a serious problem, namely poor adhesion or at least not sufficiently good adhesion to show a satisfactory behaviour in service conditions. Thus, the use of an intermediate layer which is chemically more reactive than AI2O3 could potentially improve the adhesion between the alumina coating and the substrate.
