Additively manufactured IN718 in thin wall and narrow flow channel geometries: Effects of post-processing and wall thickness on tensile and fatigue behaviors

Abstract

Using additively manufactured (AM) tubular IN718 specimens, this study was conducted to understand the effects of wall thickness, surface machining, and hot isostatic pressing (HIP) on tensile and fatigue behaviors. The tubular specimens with thin wall (TW) features and narrow flow channels (NFC) had machined external surfaces and a combination of different internal surface (machined vs. unmachined) and heat treatment (with HIP vs. without HIP) conditions. On one hand, in terms of tensile properties, HIP was found to decrease strength while slightly improving ductility under quasi-static loading. Both surface machining and larger wall thickness were found to improve ductility without influencing the strength. On the other hand, HIP, surface machining, and wall thickness had no measurable influence on fatigue performance in the low and mid cycle fatigue regimes. Some positive effects of wall thickness on fatigue life were noticed in the high cycle fatigue regime for TW specimens undergone HIP and internal surface machining. The results suggested that the post-processing steps of AM IN718 TW and NFC parts could potentially be eliminated to reduce production cost and lead time if the targeted applications were fatigue critical in low and mid cycle fatigue regimes.