Preparation and Characterization of Al–Al2O3 Composite Coatings by Cold Spray

This study investigates the effect of the mass ratio of aluminum to aluminum oxide on the structure and properties of Al–Al2O3 composite coatings deposited by cold spray deposition onto AISI 316L stainless steel substrates. Powder mixtures containing 70, 35, 30, and 20 wt.% Al2O3 were used to form the coatings, and the phase composition, microstructure, porosity, hardness, surface roughness, and tribological characteristics were studied using XRD, SEM/EDS, instrumental indentation, profilometry, and ball-on-disk testing. X-ray phase analysis confirmed the presence of metallic Al and α-Al2O3 without the formation of additional phases, while SEM analysis revealed continuous coatings with mean thicknesses ranging from 68.08 ± 1.16 to 103.39 ± 5.64 μm and an apparent porosity not exceeding 2%. The best structural and mechanical properties were observed for coating B3, prepared from a mixture of 30 wt.% Al2O3 and 70 wt.% Al: the porosity was 0.48%, the Martens hardness (HM) was 1757.6±155.8 N/mm2, and the Vickers hardness was 211.8 ± 20.7 HV. Coating B3 was also characterized by a minimum surface roughness of Ra = 0.955 μm and a relatively stable coefficient of friction in the range of 0.55–0.60. The results obtained show that the composition of 30 wt.% Al2O3-70 wt.% Al provides the favorable combination of low apparent porosity, high mean hardness, and relatively stable friction behaviour among the specimens tested.