Experimental investigations in powder mixed electric discharge machining of Ti–35Nb–7Ta–5Zrβ-titanium alloy

Abstract

The present research is the first type of study, in which the application of powder mixed electrical discharge machining (PM-EDM) for the machining of β-phase titanium (β-Ti) alloy has been proposed. β-Ti alloys are new range of titanium alloys, which has wide spread application in dental, orthopaedics, shape memory, and stents. The aim of the present study is to fabricate submicro-and nano scale topography by PMEDM process to enhance the biocompatibility without affecting machining efficiency. The effect of Si powder concentration along with pulse-current and duration on the surface and machining characteristics has been investigated. A significant decrease in surface crack density on the machined surface with 4 g/l Si powder concentration was observed. When β-Ti alloy was modified at 15 A pulse-current, longer pulse interval with 8 g/l concentration of Si powder particles, the interconnected surface porosities with pore size 200-500 nm was observed. Moreover, at Si powder concentration of 2 and 4 g/l, the recast layer thickness is 8µm and 2-3 µm, respectively. Elemental mapping analysis confirmed that PMEDM also generated carbides and oxides enriched surface, a favourable surface chemistry to enhance the biocompatibility of β-Ti alloy. Furthermore, Downloaded by [George Mason University] at 06:41 22 June 2016 2 PMEDM also enhances the machining performance by improving MRR and reducing TWR.

A Review of Additive Mixed-Electric Discharge Machining: Current Status and Future Perspectives for Surface Modification of Biomedical Implants

“…A study on the EDM of -Ti-alloy presented by Prakash et al [160] revealed a higher cell growth and adhesion on the machined surface. In similar studies, carbide and oxide layers which enhance the biocompatibility of -Ti-alloy were achieved when Sipowder was added to the EDM dielectric fluid [11]. It was also proven that the nanoporosities fabricated by PM-EDM process promote the cell growth and adhesion [161,162].…”

“…It was also reported that the white layer thickness decreases with a decrease in pulse duration (electrical energy) [152]. In addition, an EDM automatic finishing setting and the addition of powder to the dielectric fluid reduced the formation of a recast layer [11,153,154] as depicted in Figure 18.…”

“…Although a hard and adhesive recast layer is expected to enhance the corrosion and wear resistance of the metallic implant, a thick recast layer should be avoided or polished, to reduce the risk of the implant mechanical failure [149]. The recast layer thickness largely depends on the dielectric fluid type, the pulse-on time, and the powder concentration [11,38]. EDM with kerosene as dielectric fluid produces thinner and porous recast layer as well as finer and harder surface when compared to water emulsion.…”

Influence of the spark heat on the electrode behavior in Powder Mixed-EDM environment

“…Therefore, the interpretations of this decreasing are the same. Furthermore, this behavior is also recognized in trials (9,11) and (13,15), respectively. The active role of NCP particles in experiments (6,8) is continuous and reflects on the TWR for the copper electrode.…”

“…This research field is treated with various responses including the wear rate of the electrode and it is considered as one of the most significant responses in PMEDM. Most of the studies proved to decrease the Tool Wear Rate (TWR) upon the addition of the powder particles to the dielectric liquid in EDM [10][11][12]. The mixing of the powder particles with the dielectric fluid does not represent a final solution to the problems of EDM.…”