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.