Investigation of coated 316L steel surface: Surface morphology, composition, corrosion, and biocompatibility using hydroxyapatite mixed-EDM process

Abstract

316L stainless steel belongs to insufficient biological responses and corrosion resistance. Although hydroxyapatite powder (HAp)-based coating improves biological responses and corrosion resistance of the 316L stainless steel, these coatings have resulted in inferior adhesion strength and cracked surface. This study aims to synthesize a highly biocompatible and corrosion resistant coating on the 316L stainless steel with a high adhesion strength and surface integrity using the electro discharge machining (EDM) method. The study also aims to explore the impacts of process parameters on the surface features. To reach the set objectives, several characterisation methods including atomic force microscopy (AFM), scanning electronic microscopy (SEM), X-ray powder diffraction (XRD), Potentiostat (electrochemical cell), MTT assay and X-ray photoelectron spectroscopy (XPS) were adopted. The HAp-mixed EDM method synthesized a biocompatible and corrosion resistant coating with an average thickness of 14.6 μm and 20.8 MPa adhesion strength comprising of Ca-P based oxides and carbides. The modified surface showed nano surface roughness of 18.5 nm. The oxides and carbides formed in the coating improved the cell viability of 316L stainless steel surface to 87 % and corrosion resistance to 0.00123 mm per year. This study is trying to gain the attention of 316L stainless steel-based bioimplant manufacturers to launch the hydroxyapatite mixed-EDM method for concurrent machining and coating.