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Kapfenberg, Austria

Todt J.,University of Leoben | Todt J.,Austrian Academy of Sciences | Pitonak R.,Bohlerit GmbH and Co. KG | Kopf A.,Bohlerit GmbH and Co. KG | And 7 more authors.
Surface and Coatings Technology | Year: 2014

The influence of microstructure on thermal and oxidation properties of Ti1-xAlxN hard coatings is not fully understood. In this work, an Al-rich Ti0.05Al0.95N coating with a unique self-organized microstructure of alternating soft hexagonal (w) AlN and hard cubic (fcc) TiN nanolamellae synthesized by a low-pressure chemical vapor deposition (CVD) process is analyzed in terms of oxidation resistance, microstructure and phase stability, hardness as well as residual stresses. Multiple coating samples on hard metal substrates were oxidized in ambient air for 1h at temperatures in the range of 700-1200°C. Exceptionally good oxidation resistance up to 1050°C was found, whereas above 1100°C a localized surface degradation caused by the substrate-air interaction with very characteristic oxide blisters was observed. A coating hardness of about 29GPa remained in all unaffected surface areas for temperatures up to 1050°C. This is interpreted by the specific lamellae microstructure that retained a nanocomposite character even after lamellae partly decomposed during annealing. Depth-resolved stress and phase characterization performed by cross-sectional X-ray nanodiffraction in the as-deposited Ti0.05Al0.95N revealed a strong compressive residual stress gradient of up to -2GPa at the coating surface which homogenized but remained still compressive after annealing at 1050°C. Finally, it is demonstrated that the unique dense nanocomposite microstructure is responsible for the superior oxidation behavior as well as high compressive stresses in the Ti0.05Al0.95N coating. © 2014 Elsevier B.V.


Todt J.,University of Leoben | Todt J.,AUTn Academy of science | Zalesak J.,University of Leoben | Daniel R.,University of Leoben | And 7 more authors.
Surface and Coatings Technology | Year: 2016

The synthesis of Al-rich cubic AlTiN coatings represents a challenging task. Recent advances achieved using chemical vapour deposition (CVD) demonstrated the possibilities to produce (i) cubic monophase coatings with Al ratio up to x=90% and (ii) self-organized nano-lamellar AlxTi1 - xN coatings consisting of alternating wurtzite and cubic lamellae. In this work, a further development of the self-organized nano-lamellar CVD coating type is presented, namely the synthesis and physical properties of a purely cubic Al0.8Ti0.2N coating. The effect of the reduced Al content was investigated with respect to the coating's nano-lamellar microstructure, oxidation resistance, phase stability and nanoindentation hardness. Although the newly developed Al0.8Ti0.2N coating exhibited a slightly decreased oxidation resistance in comparison with the prior wurtzite-cubic nano-lamellar Al0.95Ti0.05N coating, the phase stability remained the same, while simultaneously a hardness increase of more than 30% was observed. This hardness of 36 GPa was stable up to 1050 °C, exhibiting a maximum value of 38 GPa around 950 °C. Furthermore, investigations by transmission electron microscopy revealed a modified arrangement of coherent nano-lamellae within columnar grains, forming an irregularly faceted layered coating morphology. In summary, the novel coating material grown with the rate of 5 μm per hour not only possesses a unique microstructure but attracts also by remarkable physical properties. © 2016 Elsevier B.V.


Keckes J.,Austrian Academy of Sciences | Keckes J.,Materials Center Leoben Forschung | Daniel R.,University of Leoben | Mitterer C.,University of Leoben | And 5 more authors.
Thin Solid Films | Year: 2013

We report on the spontaneous formation of periodically alternating cubic TiN and hexagonal AlN nanolamellae confined in grains of polycrystalline Ti 0.05Al0.95N thin films produced by chemical vapour deposition.The characterization was performed using X-ray diffraction and transmission electron microscopy techniques.We discuss the lamellar microstructure with the periodicity of about 13 nm and potential mechanisms responsible for the lamella formation.The finding opens the possibility to synthetize self-organized nanostructured thin films based on alternating soft and hard materials.© 2013 Elsevier B.V.All rights reserved.

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