Surface Integrity Characteristics in Wire-EDM of Inconel 718 at Different Discharge Energy

Superalloys such as Inconel 718 are widely used in turbomachinery industry due to their outstanding mechanical properties. Inconel alloys are very difficult to machine using conventional mechanical processes like broaching, milling or grinding. Wire electrical discharge machining (W-EDM) is an alternative competitive process to manufacture complex Inconel part geometries. However, surface integrity of W-EDMed Inconel components is poorly understood. This study presents the characteristics of surface integrity vs. discharge energy in W-EDM of Inconel 718. The results show that the EDMed surface topography shows dominant coral reef microstructures at high discharge energy, while random micro voids are dominant at low discharge energy. Surface roughness is equivalent for parallel and perpendicular wire directions, and average roughness can be significantly reduced for low discharge energy. The thick white layers are predominantly discontinuous and non-uniform at relative high discharge energy. Micro voids are confined within the thick white layers and no micro cracks were found in the subsurface. The thin white layers by trim cut at low discharge energy become more continuous, uniform, and are free of micro voids. Compared to the bulk material, white layers have dramatic reduction in microhardness due to significant thermal degradation. In addition, surface alloying from wire electrode and water dielectric are obvious in main cut at high discharge energy, but it can be minimized in trim cuts at very low discharge energy.