Influence of the thermal treatment of a hydroxyapatite powder on the characteristics of coatings deposited by cold gas spraying

Abstract

Usually deposited by air plasma spraying, hydroxyapatite (HAP) is widely employed as coatings for biomedical applications thanks to its biocompatibility. Over the past decades, cold gas spraying (CS) technology is of growing interest because it allows avoidance of oxidation or phase transition of materials due to lower deposition temperatures. However, spraying ceramics by CS is highly challenging and the mechanisms responsible for the deposition are not clearly described in the literature even if HAP has already been successfully sprayed by CS. In this article, the approach consists both in developing suitable HAP coatings devoted to functionalizing medical prostheses and in explaining the different steps of the deposit buildup by CS. The properties of the starting powder such as its morphology influence the quality of the final coating without any real chemical reaction with the substrate. Here it is shown how a simple preliminary thermal pre-treatment of the powder significantly affects the deposit formation and quality. The conclusions drawn in this paper demonstrate that the obtaining of a HAP coating compatible with the targeted biomedical applications requires compromises especially between the powder crystallinity and deposition efficiency.