Effect of recast layer on the low cycle fatigue life of electric discharge machined inconel 718

The effect of the recast layer formed during electric discharge machining of Inconel 718 on the fatigue life at room temperature was investigated. Data were generated in the uniaxial tension low cycle fatigue (LCF) mode at ambient temperature using flat 5 mm thick tensile specimen prepared as per ASTM E08. Taguchi's L9 orthogonal array is used to derive the experimentation outcomes for 4 different parameters with three levels. The parameters varied are peak discharge current (Ip), current pulse duration (Ton), gap voltage (V) and pulse off time (Toff). Thus machined samples were subjected to fatigue at a selected stress, and the resulting fatigue lives were compared with that of the parent end milled material. The surfaces of the fatigued specimens were examined under optical and scanning electron microscopes, and the roughness of the surfaces was measured using a standard profilometer. Analysis of the results obtained was correlated with the machining parameters and the surface quality obtained from the spark EDM process and the thickness of the recast layer formed during the process. The results obtained from micro hardness measurements, profilometry, optical and scanning microscopy were illustrated.