Papers by Author: Bülent Ekmekci

Abstract: Hydroxyapatite (HA) is bioactive and biocompatible bioceramics that is commonly used as a filler to replace amputated bone or as a coating to promote bone ingrowth into prosthetic implants. The need to overcome biocompatibility problems and improve the bone bonding ability enforced the researchers to develop suitable coating techniques. Feasibility of Powder Mixed Electrical Discharge Machining of Ti-6Al-4V alloy with HA additives in water dielectric liquid is studied as an alternative coating technique. Machined samples are analyzed by means of optical, scanning electron microscopy and energy dispersive spectroscopy. The experimental results have revealed that it is possible to deposit HA powders onto the work material surface by using the process. The morphology of the deposited material signified the dependency with respect to the operational parameters such as pulse on duration and current. Moderate pulse currents together with low pulse on duration were found to be the plausible choices for HA coating applications.

Abstract: The role of suspended particles on Ti-6Al-4V surface in Powder Mixed Electrical Discharge Machining (PMEDM) is studied using SiC powder mixing in water dielectric liquid. Surface modifications due to the additives in dielectric liquid are investigated by means of optical, scanning electron microscopy and energy dispersive spectroscopy. The attachment of added powders and surface topographies interrelated with powder suspension concentration, particle size and electrical parameters such as pulse on duration and current. The influence on discharge transitivity with respect to SiC additives is noticed with pock like features on the surface. The geometry and size of these features indicated a robust dependency with respect to operational parameters and indicated the role of secondary discharges during PMEDM. SiC particles severely transferred from di-electric liquid to machined surface at critical operational parameters and implied that the process could be also used as a surface alloying technique.

Abstract: Micro Electric Discharge Machining is mostly used micromachining technique for manufacturing of micro holes and mini cavities. It is a thermal material removal process achieved by application of recursive electrical sparks between two conductive materials immersed in dielectric liquid. There are many electrical and technological parameters, which are effective in the machining characteristics and machined material surface integrity. In this study, effects of pulse energy on characteristics of surface damage in micro electric discharge machining of micro holes are investigated. To observe the influences of investigated pulse forms, a series of micro-holes were machined and cut from cross sections for metallurgical examinations. Unconventional etching agents were applied to examine the metallurgical transformations using optical and scanning electron microscopy. It was observed that heat-damaged segment is composed of three distinctive layers, have relatively high thicknesses (0.2 to 10 μm) when compared with the size of the micro holes and varies noticeably with respect to drilling dept. Different morphological structures and deformations in the subsurface of micro-hole walls at several sections were illustrated. Finally, analyzed machining parameters and variation of hat damaged layer thicknesses were discussed in terms of drilling depth.