Microstructure and directional fatigue behavior of Inconel 718 produced by selective laser melting

Abstract

Recent research efforts in additive manufacturing have focused on developing parts made of Inconel 718 (IN 718), a nickel-based superalloy, which is an attractive material for aerospace and energy high-temperature applications. Here the selective laser melting (SLM) process is used to transform alloy powder into a solid IN 718 parts followed by optimal stress-relief and subsequent precipitation hardening treatment. Two main aspects were investigated. The IN 718 microstructure generated by the SLM process was characterized using metallographic techniques and found to be distinctly directional because it is a result of a layer-by-layer material build-up typical of the SLM process. The high cycle fatigue behavior of SLM IN 718 was determined using a novel test method designed to determine and quantify the directional material behavior, which is important information for part design and process optimization. The fatigue S-N data show that the direction parallel to the build direction is associated with the lowest fatigue strength. The role of the as-produced surface characteristics on fatigue crack initiation is discussed.