Multilayers, superlattices and nanocomposites
Multilayers and Superlattices
Improvements to the oxidation resistance, wear resistance, corrosion resistance, hardness and toughness of hard PVD ceramic thin film coatings are achieved by depositing multilayers and superlattices. These are very thin films that are formed by alternately depositing two different components to form layered structures. The coatings are referred to as superlattices when the period between the different layers is less than 100Å.
Nanocomposite ceramic coatings
A nanocomposite coating consists of at least two distinct phases: usually a nanocrystalline phase and an amorphous phase, but it can be two nanocrystalline phases. Nanocomposite theory is based on the thermodynamically driven segregation of binary, ternary and quaternary systems. The spontaneous segregation leads to a stable nanoscale structure. The use of this generic concept has led to the development of nanocomposite PVD ceramic coatings. These coatings consist of materials such as crystalline titanium, chromium and aluminium nitrides that are deposited at the same time as an amorphous material such as silicon nitride. The two materials do not mix, and result in a composite of crystalline and amorphous phases. These PVD ceramic coatings with nanometer sized grains have enhanced yield strength, hardness and toughness.