Corrosion behaviour of plasma sprayed graphene nanoplatelets reinforced hydroxyapatite composite coatings in simulated body fluid

Abstract

Hydroxyapatite (HA) coatings, reinforced with varied concentration (0–2 wt%) of Graphene nanoplatelets (GNPs) have been deposited on titanium alloys (Ti–6Al–4V) substrate using atmospheric plasma spraying. Present work studies the effect of GNP concentration on the electrochemical behaviour of the HA coatings in simulated body fluid (SBF). The HA coating exhibited 15% porosity, whereas reinforcement of 1 wt% GNPs in HA (HA-1G) shows 13% porosity, further addition of 2 wt% GNPs in HA reduced the porosity to 10%. Reduction in porosity was achieved as GNPs easily accessed the inter-lamellae to fill the gaps at inter splat region and minimized the occurrence of post-plasma spray defects such as porosity, voids, microcracks etc. These consequences nextward resulted in the significant enhancement in corrosion resistance of the matrix. HA-1G displayed a significant reduction by 67% in the corrosion rate in SBF solution, while this reduction came to 87% for HA-2G coatings. Randomly oriented wrinkles in the GNPs after corrosion process and their hydrophobic nature effectively hindered the SBF infiltration into the coating and resisted their movement towards the underlying substrate. This in turn improved the overall corrosion resistance of the system.