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A novel hydroxyapatite niobium (HA–Nb) composite coating was deposited on 316L SS substrate to improve the corrosion properties and functional compatibility of 316L SS alloy. HA–Nb coatings were applied by air plasma spray under electrical current intensities of 400, 600 and 800 A. X-ray diffraction and scanning electron microscopy techniques were utilised to investigate the characteristics of coatings. Corrosion properties were evaluated by electrochemical polarisation test in Ringer solution. Results indicated that optimum electrical current intensity for deposition of the HA–Nb composite coating on 316L SS substrate was 600 A. The composite coating improved corrosion resistance and exhibited good structural properties which in turn increased biocompatibility of 316L SS substrate. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAP) was synthesised by a precipitation method, using naturally available chicken eggshell (Ca source) and phosphoric acid (P source). The synthesised powder was electrophoretically deposited on 316L stainless steel (316L SS). The chemical composition of the synthesised powder was analysed. Ca was estimated by conventional EDTA titration and P by a gravimetric method. The Ca/P ratio was found to be 1·67, which resembles the stoichiometric HAP ratio. Fourier transform infrared (FT-IR) and powder X-ray diffraction (XRD) techniques were employed to confirm HAP formation. FT-IR spectra showed the characteristic peaks for phosphate and hydroxyl groups. The XRD results revealed that the major characteristic peaks of HAP appear in the regions of approximately 26°, 28°, 29°, 30–35°, 39°, 46°, 49° and 50° (2θ) and also indicated that no impurities are formed during HAP formation. The in vitro evaluation of HAP coated 316L SS was performed in simulated body fluid (Ringer's solution) of pH 7·4 at 37°C in a thermostatic water bath through cyclic polarisation, and the results indicated that the HAP coated 316L SS has better corrosion resistance than uncoated 316L SS. [ABSTRACT FROM AUTHOR]