Surface integrity comparison of wire electric discharge machined Inconel 718 surfaces at different machining stabilities

Current study aims to investigate the effect of machining stability on the surface integrity of the wire electric discharge machined Inconel 718 superalloy. The wire electrode material used for machining is hard zinc coated brass. Experiments were conducted at various levels of machining stabilities, defined with respect to discharge energies and machining gap conditions. The topographical characteristics were analysed by contact surface profilometer and non-contact 3D profilometer. Scanning electron microscope (SEM) images were analyzed to observe and compare the surface defects like microvoids, micro-cracks, micro globules, micro-craters on the samples machined at different stability levels. The least stable machining condition, with highest discharge energy, lowest inter electrode gap and least pulse off time, produced the most uneven topography. Recast layer (RCL) thickness was analyzed by observing the polished cross-sectional view of machined specimens under SEM. The conditions that provided the least RCL thickness were the most stable machining conditions. Furthermore, the surface layer characteristics like elemental contamination and thermal softening effects were analyzed using EDS and micro hardness tester respectively. All these characteristics have close relationship with the degree of machining stability.