High temperature oxidation and wear properties of magnetron sputtered AlTiTaN based hard coatings

Hard nanostructured TiAlN coatings have gained high importance in the field of protective tribological coatings. Nevertheless, their use regarding high temperature (>800°C) applications such as dry high speed machining still remains a challenge. Addition of elements such as Ta or Y has shown a beneficial impact on these properties. But for a better performance of these coatings, an in-depth understanding of their oxidation and wear mechanisms over a wider range of temperatures is needed which is currently unavailable in the literature. This work investigated the wear and oxidation properties of AlTiTaN hard coatings deposited by reactive magnetron sputtering at a substrate temperature of 250°C. Depending on process conditions, coatings with a preferential crystallographic orientation of cubic {111} or {200} with a columnar microstructure were observed. The oxidation and wear mechanisms for these coatings were investigated between 700°C and 950°C in air for various test durations. Further, the influence of Y doping in AlTiTaN coating was also studied.By combining Dynamic-Secondary Ion Mass Spectrometry ,X-ray diffraction (XRD) and Transmission Electron Microscopy measurements, it was demonstrated that a single amorphous oxide layer comprising of Ti, Al and Ta oxides formed at 700°C became a bilayer composed of a crystalline Al rich layer (protective Al2O3) and a Ti/Ta rich oxide layer at 900°C. The oxidation mechanism was governed primarily by inward diffusion of O at 700°C while from 800°C onwards outward diffusion of Al and inward diffusion of O controlled the reaction rate. A correlation between the oxidation kinetics and wear mechanism of AlTiTaN coatings, investigated at 700°, 800° and 900°C, was established.Doctorat en Sciences de l'ingénieur et technologieinfo:eu-repo/semantics/nonPublishe

Magnetronn sputtered hard nanostructured TiAlN coatings: Strategic approach toward potential improvement

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An uncommon cause of rapidly progressive renal failure in a lupus patient: Pauci-immune crescentic glomerulonephritis

We report a case of systemic lupus erythematosus (SLE) who presented with rapidly progressive renal failure (RPRF) with positive antinuclear antibody (ANA) and anti-double-stranded DNA (dsDNA) antibody and active urinary sediment in the form of microscopic hematuria and proteinuria. Provisional clinical diagnosis of lupus nephritis was made. Renal biopsy showed pauci-immune crescentic glomerulonephritis, the diagnosis of which was supported by positive serum anti-MPO antibody. Renal biopsy in SLE patients can sometimes reveal varied pathological entities such as antinuclear cytoplasmic antibodies (ANCAs) positive vasculitis, as in our case, which modified our treatment protocol. Thus, in a patient with SLE presenting with RPRF with active urinary sediments, ANCA serology, and renal biopsy with immunofluorescence examination should be performed always

Influence of temperature on oxidation mechanisms of fiber-textured AlTiTaN coatings

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. © 2014 American Chemical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Temperature-dependent wear mechanisms for magnetron-sputtered AlTiTaN hard coatings

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