Influence of the suspension characteristics and spraying parameters on the properties of dense suspension-HVOF sprayed Al2O3 coatings

In this work suspension-HVOF spraying (S-HVOF) was used to prepare dense and mechanical stable Al2O3 sprayed coatings with high contents of α-Al2O3 phase. Aqueous suspensions with various contents of powder (from 25 wt-% up to 50 wt-%) have been developed starting from two commercial α-Al2O3 powders, characterized by different purity and particle sizes. The suspensions have been internally injected in a modified combustion chamber of a HVOF TopGun-torch. Coating microstructures, phase compositions and mechanical properties resulting from the interaction between suspension characteristics and spray parameters are presented. Use of suspensions with high solid contents allowed the production of thick, dense and mechanically stable coatings. The α-Al2O3 was the main phase in the coatings produced through the injection of suspensions containing powders with very high purity.