Chapter 17: Thermodynamic Prediction of the Formation and Composition Ranges of Metastable Coating Structures in PVD Processes

1 Introduction

A large amount of systematic development work on new high-performance mixed carbide, nitride, boride and oxide coating materials produced by physical vapour deposition (PVD) techniques is being carried out, because the mixed coatings often display significantly improved properties ( e.g. wear-, corrosion-, oxidation-resistance or certain physical property behaviour) compared to the properties of the individual constituents.

Experiments with the deposition of metastable, multicomponent coatings using PVD methods have shown that the required coating compositions can be achieved relatively easily. Furthermore, variation of the substrate temperature as well as the coating composition sometimes allows the structure and hence the properties of the deposited coating to be changed.

By carrying out thermodynamic calculations, it is possible to predict the conditions for the appearance of different metastable phases during PVD coating processes and thereby assist in the selection of coating parameters required to produce coatings with optimum desired properties.

The general principle relating to thermodynamic calculation of the metastable phase ranges resulting from PVD of multicomponent coatings on a low-temperature substrate has been propounded by Saunders and Miodownik ^[1] as follows:

If an alloy, that in equilibrium contains a multiphase structure, is co-deposited at low enough temperatures, the surface mobility is insufficient for the breakdown of the initially fully intermixed depositing atoms, and the film is therefore constrained to be a single-phase structure Nucleation and subsequent growth processes are controlled by the substrate temperature, and therefore, if the film is constrained to be...