Liquation cracking in laser powder bed fusion-fabricated Inconel718 of as-built, stress-relieved, and hot isostatic pressed conditions

Abstract

A critical factor of the laser powder bed fusion (LPBF) additive manufacturing processed Inconel718 is its susceptibility to liquation cracking, primarily caused by the incipient melting of the grain boundary Laves phase or carbide (Nb-rich intermetallic phases). In this study, the liquation cracking behavior of the LPBF-processed Inconel718 was investigated using Gleeble® hot-ductility tests. In particular, the effect of commonly employed post-LPBF heat treatments, such as stress relieving, and hot isostatic pressing (HIP), on the liquation cracking resistance was examined. While the as-built Inconel718 exhibited good liquation cracking resistance, its liquation cracking resistance decreased after the stress relieving and HIP treatment. The variation in liquation cracking susceptibility was attributed to microstructural differences, including grain size, size and volume fraction of the low-melting carbides phase, and the segregation pattern of the solute element Nb. Good liquation cracking resistance of the as-built provides more flexibility in process design involving high temperatures. Meanwhile, HIP treatment can reduce internal defects but presents a significant disadvantage of increased liquation cracking susceptibility. These findings underscore the importance of carefully designing post-processing conditions for additively manufactured parts.