Structural properties and high temperature oxidation behaviour of Al-Ti-Ta-N and Al-Ti-Ta-Y-N coatings

• Increasing Y contents affect the as-deposited texture and lattice parameter.
• Y affects relative growth rates of Al2O3 and TiO2 in oxidationexperiments.
• Y leads to slower forming, more protective Al2O3 top layer.
• Isotopic oxidation shows outward Al/inward O2 oxidation mechanisms as in Al-Ti-N.
• SIMS shows an Al-depleted region near the unoxidized nitride.

The as-deposited structural properties and the high temperature oxidation mechanisms occurring in Al-Ti-Ta-N and Al-Ti-Ta-Y-N are studied. Yttrium causes structural changes (lattice parameter, texture) depending on the deposition temperature. In oxidised Al-Ti-Ta-Y-N some alumina crystallises in the Ti-rich oxide, because of Y. SIMS shows a transition layer between Al-rich and Ti-rich oxides and a shallow unoxidized Ti-rich region at the interface with the nitride in both materials, not reported before, explained with SIMS of isotopically oxidised samples. The main effect of Y on Al-Ti-Ta-N is decreasing the kinetics of formation of alumina, making it more uniformly spread and protective.

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