Nihal Ekmekci

Wear-resistant Hydroxyapatite (HA)-involving biocompatible surfaces are needed in medical applications. In this context, the surface of biomaterial Ti6Al4V alloy were functionised by Electrical Discharge Machining (EDM) with and without HA powder addition. Nano and micro HA fine powders were used as additives in Deionized Water (DW) dielectric. As electrical parameters, 7 and 22 A pulse current (Ip), 100 and 1600 µs pulse on duration (ton) were employed to meet the highest HA migration rate to the EDM-modified surface. The surface properties were investigated by Scanning Electron Microscope (SEM), Energy-Dispersive Spectroscope (EDS), and X-ray diffractometer (XRD). It was confirmed that HA powder additives alter the machined surface properties significantly under specific electrical parameters. Tribological investigations were conducted concerning the wear rate and coefficient of friction (CoF). The tribological performance of HA powder mixed EDM’ed surfaces were compared to the performance of EDM’ed and reference sample surfaces. Finally, surfaces modified by nano HA additives are found to be more resistant to wear than other cases. This study reveals that HA powder mixed EDM is a promising alternative machining method to provide wear-resistant as well as HA rich surfaces for biomedical industry.

Titanium surface modification by the Hydroxyapatite (HA) mixed Electrical Discharge Machining (EDM) is an alternative and promising technique to enhance the biocompatibility and to promote the biological performance in bone, which is dependent on surface properties, such as surface roughness, chemistry, and wettability. HA powder is used for the first time with electrical discharge machining to improve osteoblastic cell activity on the developed surfaces for Ti6Al4V. Different HA concentrations in deionized water were tested as an experimental variable during EDM. Abrasive polishing and electrical discharge machined control surfaces without powder addition also analyzed to compare the results. The surface characteristics of analyzed samples were evaluated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffractometry (XRD), white light interferometry, and contact angle measurements. The wettability tests suggest that the hydroxyapatite powder mixed EDM’ed surfaces shows highly hydrophilic characteristics compared the other surfaces, abrasive polished and EDM’ed without powder addition in the dielectric. The results from the MTT assay revealed that those surfaces modified using HA powder addition in distilled water dielectric liquid promoted the most significant cell attachment/growth. The results indicate that HA powder mixed EDM offers a promising method for the surface modification of biomaterials such as titanium alloys

Added powders in a dielectric medium substantially influence the features of electrical discharges due to altered interelectrode conditions during the electrical discharge machining (EDM) process. The main discharge channel is disturbed due to the added powders in dielectric liquid and leads formations of secondary discharges. Such altered discharge conditions generate a unique topography on the machined surface and consequent subsurface microstructure beneath it. Ti6Al4V work material machined using SiC powder mixing in de-ionized water for an extensive set of pulse-on duration and pulse currents. Then, different forms of secondary discharges were identified from the resultant surface features and corresponding subsurface microstructures. The results pointed out that generation of unevenly separated secondary discharges increased the material transfer rate from the powder mixed dielectric liquid to the machined surface by means of the decomposed ions in the plasma channel. Complete separation of the main discharge channel into evenly distributed secondary discharges is possible under specific machining conditions that suggested minimal deformation of the machined surface regarding microcracks, roughness, and heat affected layer thickness. Under such machining conditions, another means of material transfer mechanism is activated that lead a powder particle build-up process on the machined surface. Consequently, five different discharge forms were proposed to describe the resultant surface topographies and subsurface microstructures. The material migration phenomena and the mechanisms are discussed in relation to the pulse-on time and pulse current.

Hydroxyapatite (HA) powder suspension in deionized water was used as a dielectric liquid during electrical discharge machining (EDM) of Ti6Al4V work material. The machined surfaces were evaluated by scanning electron microscopy (SEM), energy dispersive spectroscopy, and optical microscopy. The powder particles in the dielectric liquid extensively migrated and formed an HA-rich layer on the work material surface under specific machining conditions. The result was attributed to the generation of secondary discharges due to altered discharge conditions. The particles divided the primary discharge channel into several secondary ones. When the main discharge channel subdivided into several sub-discharges with comparable energy densities, the particles in the discharge region got stuck among them. Then, they moved toward the melted cavities and penetrated the surface at the end of the discharge duration. The results suggest the process as a practical alternative for producing biocompatible interfaces or coatings for medical applications.

The discharge gap phenomena in powder-mixed electrical discharge machining are examined using SiC powder mixing in water dielectric liquid. Surface modifications on machined work materials are investigated by means of optical, scanning electron microscopy and energy-dispersive spectroscopy. The experimental studies revealed that the surface morphology drastically affected the additives as means of secondary discharges and particle migration from dielectric liquid. Such mechanisms do not occur randomly and indicate a robust dependency with respect to powder suspension concentration, pulse on duration and current. The influence on discharge transitivity with respect to suspended particle concentration is noted with pock shape development due to secondary discharges followed by an intermediate stage signifying a sudden increase in particle migration from the dielectric liquid. The particles decomposed on the surface at specific operational conditions demonstrating the possibility of methodical surface alloying using the process. Finally, the mechanisms involved were elaborated with respect to operational parameters and discussed based on the experimental results.

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.