Investigation of the effects of sintered silver-hydroxyapatite powder-added electrodes on biological compatibility in electrical discharge machining

Electrical discharge machining is based on the principle of removing material with the use of consecutive electrical discharges between a work-piece and an electrode placed on a distance in a dielectric liquid. Extremely high-temperature values are achieved during the process ( ̴ 20000K). Surface topographical features generated during the process are depended on the operational parameters such as the electrode type, dielectric liquid, pulse duration, pulse current, and open gap voltage. Electrical discharge machining is widely used in processing hard materials with complex geometries as well as heat-resistant materials. Ti-6Al-4V alloy is a preferable material for biomedical implant applications due to its low Young's modulus, high mechanical features, and corrosion resistance. It has been noted that Al and V alloying elements release ions when interacted with body liquid for a long period and cause several diseases such as Alzheimer's, neuropathy, or osteomalacia despite the good biocompatibility properties of Ti. Therefore, various studies have been conducted in the literature to enhance the bonding and biocompatibility properties of implant surfaces by applying different physical, chemical, and mechanical methods that change the surface roughness, topography, and chemical composition of titanium alloys surfaces. In this thesis study, a porous surface coated with silver calcium phosphate similar to the structure of bone has been tried to be obtained by using the high mechanical properties of Ti-6Al-4V material, the biocompatibility of hydroxyapatite, conductivity, and antibacterial properties of silver. Micronized silver and hydroxyapatite powders were mixed in different proportions and 4 tool electrodes were produced by powder metallurgy. Then, experimental groups were planned by using the electrodes produced by the powder metallurgy. 39 samples were electrical discharge machined in pure water dielectric liquid by using 3 different pulse currents and 4 different pulse duration. The surfaces of the samples were analyzed by using optical microscopy, scanning electron microscopy and, an X-Ray diffractometer. The findings suggested the possibility to obtain functional surfaces enriched with silver-hydroxyapatite powders, consisting of craters in the form of pores resembling the structure of the bone. Finally, it has been concluded that the use of powder metallurgy electrodes in electrical discharge machining will be an alternative and promising method for prospective studies.