Effects of dispersed α-Al2O3 particles into a cold-sprayed aluminium coating on its subsequent oxidation by the PEO process

Abstract

The present study focused on the use of a duplex surface treatment combining cold-spray deposition and plasma electrolytic oxidation (PEO) to produce an aluminium metal matrix composite coating, including dispersed α-Al2O3 particles, with improved tribological properties. Al/α-Al2O3 composite coatings were first deposited by cold-spray, with various thickness and proportion in α-Al2O3 particles, and, then partially oxidized by PEO under various processing durations and sparking regimes (arcs or soft regime). The feasibility of cold-spraying thick, compact and adherent aluminium coatings containing well-dispersed α-Al2O3 particles (up to 14 vol%) was demonstrated in this work. It was also pointed out that the addition of hard α-Al2O3 particles into the spray composition tends to densify the deposited aluminium coating. This was related to a stronger peening effect which, in turn, decreases the growth kinetic of the subsequent PEO oxide layer. The presence of dispersed α-Al2O3 particles was found to promote the formation of the corundum alumina phase in the PEO oxide layer by triggering the transition to the soft sparking regime earlier. It was also observed that dispersed α-Al2O3 particles remain unaffected throughout the PEO oxide layers formed within the conventional arcs sparking regime while they undergo a morphological transformation within the specific soft sparking regime. This was explained by considering the different type of micro-discharges that initiate during each regime. Finally, sliding wear tests revealed that the incorporation of α-Al2O3 particles into the cold-sprayed coating resulted in a slight decrease in the friction coefficient and the wear rate of the produced PEO layers.