title: Influence of temperature on oxidation mechanisms of fiber-textured AlTiTaN coatings.
abstract: The oxidation kinetics of AlTiTaN hard coatings deposited at 265 °C by DC magnetron sputtering were investigated between 700 and 950 °C for various durations. By combining dynamic secondary ion mass spectrometry (D-SIMS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) investigations of the different oxidized coatings, we were able to highlight the oxidation mechanisms involved. The TEM cross-section observations combined with XRD analysis show that a single amorphous oxide layer comprising Ti, Al, and Ta formed at 700 °C. Above 750 °C, the oxide scale transforms into a bilayer oxide comprising an Al-rich upper oxide layer and a Ti/Ta-rich oxide layer at the interface with the coated nitride layer. From the D-SIMS analysis, it could be proposed that the oxidation mechanism was governed primarily by inward diffusion of O for temperatures of ≤700 °C, while at ≥750 °C, it is controlled by outward diffusion of Al and inward diffusion of O. Via a combination of structural and chemical analysis, it is possible to propose that crystallization of rutile lattice favors the outward diffusion of Al within the AlTiTa mixed oxide layer with an increase in the temperature of oxidation. The difference in the mechanisms of oxidation at 700 and 900 °C also influences the oxidation kinetics with respect to oxidation time. Formation of a protective alumina layer decreases the rate of oxidation at 900 °C for long durations of oxidation compared to 700 °C. Along with the oxidation behavior, the enhanced thermal stability of AlTiTaN compared to that of the TiAlN coating is illustrated.
authors.affiliation: Centre de Recherche Public-Gabriel Lippmann , Science and Analysis of Materials Department, Belvaux L-4422, Luxembourg.
authors.forename: Vishal
authors.initials: V
authors.lastname: Khetan
authors.forename: Nathalie
authors.initials: N
authors.lastname: Valle
authors.forename: David
authors.initials: D
authors.lastname: Duday
authors.forename: Claude
authors.initials: C
authors.lastname: Michotte
authors.forename: Marie-Paule
authors.initials: MP
authors.lastname: Delplancke-Ogletree
authors.forename: Patrick
authors.initials: P
authors.lastname: Choquet