Thermochemical modelling of the phase stability of coatings deposited from the gas phase

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(Ti1-xAlx)N coatings are widely used for e.g. cutting toolapplications on account of their wear resistance at elevatedtemperatures. In the system (Ti1-xAlx)N, the transformationfrom the metastable cubic phase, with excellent tribologicalproperties, to the metastable hexagonal phase, with inferiorcoating properties, occurs in a range of 0,4 x 0,91, asreported by different authors. The reasons for the ratherextensive variation in the critical aluminium concentration atwhich the hexagonal phase appears are not evident.The aim of the proposed project is to contribute towardsunderstanding the reasons for this rather exensive variation.We seek to expand an existing thermochemical model, based oncomparing the Gibbs energy of stoichiometric and defect freeindividual structures to include variations in stoichiometry aswell as the presence of grain boundaries.Hence, we suggest to systematically, investigate therelationship between film stoichiometry, grain size and thestructure formed (cubic and/or hexagonal). We anticipate thatthis model will contribute significantly to a better basicunderstanding of the reasons for the above discussed differentcritical aluminium concentrations reported. In addition, such amodel will enable prediction of the coating constitution. Thiswould represent significant progress significant progress forthe production of coatings from the gas phase as compared tothe usually applied trial and error methods.