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- Alumina (1)
- Coating (1)
- Film analysis (1)
- Oxide film formation (1)
- Residual stress (1)
- Sol-gel (1)
- Wear protection (1)
- Wear resistance (1)
Aluminium oxide films were prepared by a dip-coating procedure from solutions of hydrolysed aluminium-tri-sec-butoxide in methoxyethanol on austenitic steel as well as hard metal tools. The heat treatment was performed in an argon atmosphere or vacuum at temperatures up to 1100 °C. Characterisation of the coatings by SEM, showed nearly crack free coatings with a dense morphology which completely cover the substrate. The chemical composition of the coatings was investigated by ESCA, GD-OES and XRD measurements. This analysis detected a multi-layered arrangement of spinel phases, ?- and ?-alumina in the coatings. The scratch test showed sufficient adhesion of the coatings comparable to CVD layers. Pin-on-disc and oscillating sliding tests were carried out on solgel coated samples and also on uncovered reference samples. The determined wear rates and friction coefficients showed significant improvement in wear resistance of solgel coatings containing a corundum phase. The strong adhesion to the substrates is due to a layered assembly formation and gradient composition of the coating caused by an interdiffusion of metal cations and oxygen in the metal/oxide interface during heat treatment.
The aluminium oxide films on austenitic steel are prepared from sols of re-dispersed boehmite nano powders in water. After dip-coating of the sol, a heat treatment including drying, calcination and annealing in vacuum at temperatures up to 1100°C is performed to obtain crack-free coatings of a thickness up to 6 µm. XRD measurements detect α- and γ-alumina, a TiOx-phase at the metal/coating interface and a gradient of phase formation in the coating. The strong adhesion on the substrates is due to the layered assembly and gradient composition of the coating caused by an inter-diffusion of metal cations and oxygen in the metal/oxide interface during heat treatment. Residual stress measurements by X-rays result in compressive stresses of 24 GPa in the alumina coatings. The pin-on-disc test shows a remarkable improvement of wear resistance obtained by sol-gel coatings. The α-alumina content and the compressive stress of the coatings correlate with wear resistance of the coatings.