Influence of Process Parameters and Heat Treatment on the Fatigue Performance of Inconel 718 Fabricated Through Selective Laser Melting

Many critical process parameters affect the fatigue performance of super alloys produced by Selective Laser Melting (SLM). These parameters affect the microstructure, surface roughness, and defect formation and play a significant role on the fatigue life of the super alloys. Optimizing these parameters in combination with appropriate post-processing techniques is crucial to extending fatigue life by decreasing defects. In the present work two set of Inconel718 (IN718) samples were prepared under two different energy densities. According to ASTM E606, a low cycle fatigue test is conducted to assess fatigue performance. Samples with lower energy density showed better fatigue life (Nf) of 858 number of cycles under strain amplitude of 0.8% and the corresponding stress amplitude is 866 MPa. Solution plus Single Aging heat treatment (HT) is adopted to dissolve the brittle lave phase and precipitates γ and γ′ phases to enhance the microstructure of alloy. Selective laser melted IN718 have unique microstructure due to the quick solidification and frequent thermal cycling involved in the process. In order to investigate the microstructure and metallurgical evolution, Optical microscopy (OM), Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Energy-dispersive X-ray spectroscopy (EDS) analysis were carried out. OM images showed equiaxed grains compared to coarse columnar crystals in as-built counter parts. Back scattered electron images showed the presence of δ phase in grain boundaries in addition to some irregular laves phases. X-ray diffraction study identifies the fcc structures (γ, γ′) and corresponding lattice planes. The present study establishes a relationship with process parameters, heat treatment and fatigue properties of selective laser melted IN718.