Effect of number of coatings on structure, mechanical properties and corrosion behaviour of HA coating on 316L stainless steel

Deepak Narang and Uma Batra

Abstract

In this study, hydroxyapatite coatings were deposited on AISI 316L stainless steel using sol–gel dip coating method. The three coatings were developed by subjecting the substrate to three; four and five times dip in the sol. The surface morphology and elemental analysis of coatings were studied using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The porosity in coating was determined using inverted metallurgical optical microscope (Zeiss Axiovert 200 MAT) fitted with imaging software (Dexel, version 1.3.4). The surface roughness was determined using surface testing machine (Surftest, Mitutoyo, model SJ-400) for a cut-off of 0.8 mm. The micro hardness test on coated samples was conducted using a Vicker’s micro hardness tester (model HV-1000 V, Huayin). The adhesion strength of the coatings was calculated using Hertz equation. The coating developed by four times dip demonstrated the minimum surface roughness; maximum micro hardness and adhesion strength. In order to investigate the corrosion behavior of uncoated and hydroxyapatite coated 316L stainless steel, electrochemical potentiodynamic polarization tests were performed in physiological solutions at 37±1◦C. The coating developed by exposing substrate for four times dip in sol. offered a better corrosion protection of the substrate compared to coatings developed by exposing for three or five times dip in sol.