Investigation of surface properties of monolayer and bilayer biomedical coatings applied to titanium and cobalt based alloys produced by additive manufacturing method

The production of patient-specific implants is gaining increasing significance in biomedical applications, with additive manufacturing methods emerging as a pivotal technology in this domain In this study, Ti6Al4V and CoCrWMo alloys were produced using Selective Laser Melting (SLM), a widely used additive manufacturing technique. To enhance their biocompatibility and surface characteristics, three different biomedical coating configurations were applied: single-layer Titanium (Ti), single-layer Hydroxyapatite (HA), and dual-layer Ti/HA coatings. The deposition of these coatings was performed using the flame spray method, known for its cost efficiency and ease of application. The microstructural properties of the coatings were investigated through Scanning Electron Microscopy (SEM), and their elemental composition was characterized using Energy Dispersive Spectroscopy (EDS). Phase structure and crystalline transformations were examined by X-ray Diffraction (XRD). The coating thickness and surface roughness were measured, and the adhesion strength between the coating and the substrate was determined by performing a scratch test. In vitro wear and corrosion experiments essential for assessing biomedical performance were carried out in Lactated Ringer's solution to replicate physiological conditions. As a result of the study, single-layer Ti, HA and bilayer Ti/HA coatings were successfully applied on both Ti6Al4V and CoCrWMo substrate materials. Upon examination of the coating results, the bilayer Ti/HA coatings exhibited higher surface roughness compared to the single-layer coatings. This increase is considered a favorable feature in terms of cell adhesion. In bilayer coatings, the presence of the intermediate Ti layer was found to enhance the adhesion of the HA coating to the substrate, which positively influenced both wear and corrosion resistance. Microstructural analysis also revealed that the formation of macro cracks was reduced in bilayer coatings, and the overall coating integrity was more stable.