Hydroxyapatite and YSZ Reinforced Hydroxyapatite Coatings by Gas Tunnel Type Plasma Spraying

Abstract

Chemical structure of hydroxyapatite (HA) is very close to human bone which makes it compatible with the tissue of the human body. Its good biocompatibility makes it to be used extensively in many prosthetic applications, especially as a porous material for optimal bone in growth. Currently, this material is being deposited on bio-inert metallic implants and used as recovery parts in human body. In this present study a high-power plasma jet known as gas tunnel type plasma torch (GTTP), was used to produce HA and YSZ reinforced HA coatings on stainless steel substrate. In this study, microstructure, tribological properties and bioactivity of the GTTP sprayed HA and YSZ reinforced HA coatings was investigated. The XRD spectra of the as-sprayed coatings showed that the as-sprayed pure HA coating retained its crystalline HA phase similar to the initial feed stock HA powder, even though there existed a possibility for occurrence of decomposition during its in-flight in high temperature plasma zone. In the present case the decomposition processes of in-flight HA could be well controlled by means of selective operating parameters and unique nature of GTTP jet. The presence of un-melted particles and pores inside the coating microstructure play a vital role in the bonding strength of the coating.