Microstructural Changes in Inconel 625 Alloy Fabricated by Laser-Based Powder Bed Fusion Process and Subjected to High-Temperature Annealing

Abstract

The microstructure of the laser powder bed additively manufactured Inconel 625 in post-build stress-relief annealed condition and subsequently annealed at a temperature of 600 °C for 5, 100 and 500 h was investigated by means of light microscopy as well as scanning and transmission electron microscopy. Stress-relieved Inconel 625 exhibited fine cellular–dendritic microstructure characterized by the high dislocation density. Selected area electron diffraction studies allowed to demonstrate that already after 5 h of annealing at a temperature of 600 °C, precipitation of the γ′′ phase in the form of coherent nanoparticles occurred. With the prolongation of the duration of annealing at a temperature of 600 °C from 5 to 500 h, the gradual dissolution of intercellular areas and decrease in the dislocation density were accompanied by enhanced precipitation of the γ′′ phase nanoparticles.