Post-processing of Inconel 718 superalloy by Laser-based Powder Bed Fusion: Microstructures and properties evaluation

Abstract

In this work, IN718 superalloy has been additively manufactured through Laser-based Powder Bed Fusion (PBF) process. The present investigation aims to study the effect of post printing heat treatments on the metallurgical aspects, such as phases, crystallographic texture, microstructure evolutions and the mechanical properties. Heat treatment optimization has been pursued to achieve a better combination of strength and ductility. PBF fabricated material was further subjected to different heat treatments, comprising of homogenizing, solutionizing and ageing. Material was characterized with respect to the building direction (BD). As-printed specimen exhibits face centered cubic (FCC) γ matrix along with minor amounts of other phases. The melt pool boundaries were found to be rich in Niobium and Molybdenum, indicating segregation during fabrication. Upon post-heat treatments these segregations dissolved considerably. Heat treated microstructure exhibited homogeneously dispersed γ′ and γ′′ phases, and relatively small fractions of carbides, acicular and plate shaped δ phases. Heat treatments led to a significant increase in hardness (by about 54 %) and tensile strength (by about 45 %) while retaining considerable ductility.