Microstructure and mechanical properties of alumina coatings prepared by double glow plasma technique

Abstract Low-temperature growth (600 °C) of α-Al 2 O 3 coatings on the stainless steel substrate by double glow plasma technique was achieved. The compositions and microstructures of the coatings prepared at different oxygen flow rates were characterized, respectively, by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometry. A phenomenological mechanism for the formation of the Al 2 O 3 ceramic coatings during the oxidation process was proposed on the basis of the experimental results. It was obvious that the oxygen flow rates had a great effect on the surface structure of the prepared Al 2 O 3 coatings. The dense and smooth Al 2 O 3 coatings were prepared at the oxygen flow rate of 15 sccm. In addition, the correlations between the mechanical properties of Al 2 O 3 coating and oxygen flow rates were also discussed. The coating prepared at 15 sccm oxygen flow rate exhibited the best mechanical properties with a maximum hardness of 31 GPa and elastic modulus of 321 GPa. The corresponding critical load of scratch adherence for this sample was 47 N.