DEVELOPMENT OF BIOACTIVE HYDROXYAPATITE COATINGS ON TYPE 316L STAINLESS STEEL BY ELECTROPHORETIC DEPOSITION FOR ORTHOPAEDIC APPLICATIONS

摘要

Hydroxyapatite (HAP) has been deposited on type 316L SS by electrophoretic deposition method from a suspension in isopropyl alcohol. The coated samples were sintered at 800 deg C for one hour in vacuum for diffusion and adherence of the coating to the substrate. The coatings were deposited for various durations at 60 V in order to establish optimum coating parameters. The coatings obtained at 60 V for 3 minutes deposition time showed good properties. The various phases present in the coatings were analyzed using XRD, while secondary ion mass spectrometry (SIMS) was used to analyse the chemical composition across the coated substrate. XRD analysis confirmed the phase purity of HAP coatings, and SIMS analysis indicated the presence of a metal-ceramic diffusion interlayer. Open circuit potential (OCP)-time measurements, potentiodynamic cyclic polarisation and electrochemical impedance spectroscopy (EIS) were carried Out in Ringer's solution to study the corrosion behaviour of HAP coated samples in comparison with the uncoated one. The OCP and breakdown potentials shifted towards the noble direction for the HAP coated specimens. Scanning electron microscopic (SEM) observation did not show any pits developed on HAP coated surface while pits were seen on uncoated substrate. Higher polarisation resistance and lower capacitance values were obtained for HAP coated samples immersed for 240 h in Ringer's solution. indicating the stable nature of the coatings. The HAP coated materials evinced improved corrosion resistance in comparison to the uncoated type 316L SS. The results indicate that electrophoretic deposition can provide a phase-pure HAP top layer with an anticorrosive interlayer, which should show good corrosion resistance in the human body environment.