Bio-ceramic Composite Coatings by Cold Spray Technology

Bioceramics such as hydroxyapatite (HAP) have been conventionally deposited by plasma spray technique. However, due to the inherent high temperature in the plasma, deleterious effects such as evaporation, phase alteration, residual stress, debonding, and gas release etc., commonly occur in these coatings. This paper presents a novel approach to deposit bioceramic coatings at temperatures well below their melting point by cold spray, using composite powders of titanium and HAP. The influence of the process parameters, powder type as well as HAP to titanium ratio has been investigated. It was observed that dense composite coatings, containing up to 30% HAP can be deposited by this technique. Due to widely differing physical characteristics between the powders, as well as the adhesion mechanism, the HAP content in the deposit was a few percent lower than the powder mixture. XRD analysis indicated that the phase composition of the HAP in the deposit was identical to that of the powder. Further, the bond strength of the deposit was comparable/better to that of the plasma sprayed HAP. Coatings deposited using this process hold tremendous potential for improving bone integration of a wide range of dental and orthopedic implants.