Studies on the effect of SiC nanopowder concentration and discharge energy on surface roughness and recast layer in micro ED milling of Inconel 718 alloy

Abstract Micro-EDM is one of the most viable processes for micromachining hard and conductive materials. However, the slow machining rate, high tool wear rate, and poor surface quality caused by the inherent nature of the material removal mechanism continue to pose significant challenges. This study explores the impact of silicon carbide (SiC) nanopowder (25 nm–35 nm) blended dielectric on micro-electro discharge milling of Inconel 718 alloy. The experiments were conducted using a multipurpose micromachining center equipped with a rotating spindle and Resistor Capacitor type micro-EDM module. Micro-channels were machined using various concentrations of SiC nanopowder (0 to 0.4 g l −1 ) in the dielectric fluid, under different discharge energy levels ranging from 7.2 μJ to 720 μJ. The process was controlled by a specialized dielectric circuit that used ultrasonic agitators and mechanical stirrers to ensure uniform nanopowder distribution during machining. The surface roughness, crater diameter and recast layer thickness were analysed. The results showed that adding SiC nanopowder reduced surface roughness up to 19.15% across all discharge energy ranges. This reduction was due to the nanopowder lowering the dielectric breakdown voltage, increasing the inter-electrode gap, and distributing energy more evenly, which resulted in smaller and more uniformly distributed craters. Surface roughness decreased further as the nanopowder concentration increased. Additionally, the study found that the inclusion of SiC powder reduced the thickness of the recast layer up to 55.3% at all energy levels by reducing the energy per spark and enhancing the removal of molten material. High-Resolution Scanning Electron Microscope (HRSEM) and Energy Dispersive x-ray Spectroscopy (EDS) analyses revealed that material migration onto the machined surface was minimized, and surface defects such as microcracks and voids were less prevalent at lower energy levels. Overall, SiC nanopowder improved the surface quality and reduced the white layer thickness in micro-EDM milling of Inconel 718.