New Hard Nanocomposite Coatings with Addition of Cr or Reactive Elements: Tribofilm Formation and Effect of Added Elements on Spinodal Mechanism - SPITRICOAT

Institution CRP Gabriel Lippmann
Partenaire(s) : Cératizit S.A. , University of Leoben (Austria)
Du : 01/05/2010
Au : 31/03/2013
Budget : 484 000,00€
Contact(s) : Migeon Henri-Noël , Valle Nathalie

Summary

Although Ti-Al-N coatings are widely used in industry, their good wear resistance at high temperature is not sufficient for specific applications like dry high speed machining of composite materials. Different alloying elements were then added to improve wear and oxidation resistance at high temperature of such coatings. Among the alloying elements, Si and Ta are particularly interesting for high temperature applications.

They lead to nanocristalline structure which consists of 3–10 nm small nanocrystals of a hard transition metal nitride such as TiAlN surrounded by an amorphous monolayer Si3N4 phase which give the cohesion strength to the system. In order to get better wear and oxidation properties at high temperature (>900°C), we propose an original approach consisting in the addition of one reactive element (Y, La..) or Cr in Al-Ti-Ta-N nanocomposite coatings. The idea is to use doping to improve the chemical de-mixing energy of nanocristalline (e.g. (Ti,Al)N) phase and amorphous phase (e.g. TaN), to increase the coherence of the interface between amorphous and crystalline phase and thus to improve the coating chemical stability and tribological properties at high temperature.

This study will be focalized on the elaboration of such new Al-Ti-Ta-N- based nanocomposite coatings (PVD) and their characterization in their initial, oxidized and worn states (TEM, XPS, XRD, SIMS, Atom Probe,...). By studying microstructure, composition, high temperature oxidation and wear resistance of the deposited coatings, the nanostructure, which generated the best-performing coatings will be identified. Moreover, this study will give us a deeper knowledge for the growth of nanocomposite coatings, the mechanisms of oxidation and the tribofilm formation.