The investigation of effect on the surface properties of micronized hydroxyapatite powder additive in electrical discharge machining

Electrical Discharge Machining (EDM) is one of the non-traditional production process and it is based on material removal by thermal effect of sparks which are formed by applied consecutive electrical pulse voltages between workpiece and electrode inside the dielectric. Very hard and complex parts can be machined easily due to the thermal nature of the process and the absence of cutting forces during machining. In this method, applied pulse current, pulse duration, pause duration, open gap voltage, workpiece material, tool electrode and dielectric liquid are the direct affecting factors for machining and surface finish. In Powder Mixed Electrical Discharge Machining (PMEDM), increasing the machining performance by the effect of powders which are added to dielectric and suspended in dielectric is aimed. Titanyum alloys are preferred in medical applications due to the good corrosion resistance and excellent mechanical properties. It needs to be coating with the materials good interaction with bones due to the regional corrosion of interactions with body fluid and ion release into surrounding tissues or problems in integration with bones. Hydroxyapatite (HA) is a biocompatible bioceramic which is generally used as filler in amputed bone or support for the implants. Manufacturing and using as implants, reliability, have no viral or bacterial risk and bioinert ceramics have no interaction with living texture environment are the advantages of bioceramic.So, they are preferred for coating of medical metals. In this study, surface characteristics of EDM'ed Ti-6Al-4V alloy by adding the micronized hydroxyapatite powder to dielectric are aimed. Parametric series of experiments consisting of 40 samples are employed by using different pulse duration and different pulse current. Machined samples are investigated by scanning electron microscopy, X ray difractometry and optic microscopy. HA-rich structures are identified and the parameters at which these structures occured are determined. It is observed that, the best result of 7,12, 22, 42 Amper pulse current is 22 Amper and between 100-1600 µs pulse duration. Obtained result showed that, machinability of complex part at the same time the HA-rich functional surfaces are possible.