Role of Surface Cracking and Recast Layer Deposition on Formation of Hardened Layer During EDM of Inconel 825 with Varied Electrode Material

White layer or recast layer is considered one of the machining-induced surface defects during electro-discharge machining (EDM). In the present work, aspects of recast layer formation are studied during EDM of ‘difficult-to-cut’ aerospace superalloy Inconel 825. Effects of peak discharge current on the thickness of the recast layer are studied in relation to different electrode materials used: Copper and copper–nickel (90% Cu and 10% Ni). Formation of recast layer attributes to a hardened layer, just beneath the machined surface. This is further verified through the microhardness depth profile, which exhibits a strong dependence on recast layer thickness. In addition, EDMed surface morphology is characterized by crack density, which depends on peak discharge current as well as properties of tool electrode.