Optimization of Deposition Parameters for α-Al2O3 Coatings by Double Glow Plasma Technique

The parameters to prepare α-Al2O3 coatings by double glow plasma technique were optimized to obtain dense and thick α-Al2O3 coatings on 316 L stainless steel at low temperature of 580 °C. The parallel distance between the source electrode and the substrate, working pressure, source electrode voltage, and workpiece electrode voltage were designed by L9 Orthogonal array design. The thickness, microstructure, chemical composition and phase components of the sputter-deposited Al/α-Al2O3 coatings were analysed by means of 3-D non-contact surface profiler analysis, scanning electron microscopy equipped with energy dispersive X-ray spectrometry and glancing-angle X-ray diffraction, respectively. The results indicated that the parallel distance between the source electrode and the substrate played a dominant role in determining the thickness of the films. The coatings prepared at the optimum parameters exhibited a very dense, uniform, and compact microstructure without any cracks and defects. It was found that iron aluminide formed at the interface between the coatings and the substrates. The thickness of the coatings reached about 11.6 μm at the deposition rate of ~64.4 nm min–1. The oxidized coatings with the lowest porosity about 0.13 % had relative content of α-Al2O3 as high as 66.5 % when oxygen flow was 2 sccm.