Multi-walled carbon nanotubes in powder mixed electrical discharge machining: an experimental study, state of the art and feasibility prospect

The present study explores the effectiveness of powder mixed electrical discharge machining (PM-EDM) by utilizing the unique properties of multi-walled carbon nanotubes (MWCNTs) on machining of hard-grade medical alloy (β-type titanium). To investigate the capabilities of the PM-EDM in terms of machinability, biocompatibility, tribological characteristics and surface integrity, the experiments were conducted according to the L18 orthogonal array. The analysis of variance (ANOVA) technique was employed for identifying the significant process parameters affecting metal removal rate (MRR). The ANOVA results revealed that the dielectric medium was the most significant factor that majorly affects the MRR (63.25 mm3/mm) and it was followed by the peak current (Ip), pulse on (pon), pulse off (poff) and electrode material. A 15A peak current at pulse-on/pulse-off time of 100/20 μs by using MWCNTs in the dielectric medium with a tungsten/copper tool electrode is the optimum parametric set. The biocompatibility of machined surfaces was scrutinized by cytotoxicity test which confirmed that the machining with MWCNTs elevated the biological responses of reformed surface and contributed to achieve the cell viability of 94%. The pin-on-disc wear results revealed that MWCNTs machined surface had the least value of wear rate and acted as a low frictional surface. Also, the recast layer produced after MWCNTs machining adhered strongly to the base material and exhibited twofold adhesion strength as compared to the water machined substrate. The formation of oxides and carbides in the presence of MWCNTs entities contributed to the tribological behaviour and biocompatibility of alloy. Thus, the excellent assets of MWCNTs elevate the potential of EDMing by diminishing the bottlenecks like the creation of surface defects in conventional EDM (deionized water medium) at high discharge energies.