Elucidating the Effect of Sintering Time on the Process-Structure-Property Relationship of Inconel 625 Produced by Metal Extrusion Additive Manufacturing

Abstract

Inconel 625 (IN625), a Ni-based superalloy valued for its strength and corrosion resistance, is known to suffer from microcracking during fusion-based additive manufacturing. Metal Extrusion Additive Manufacturing (MEAM) offers a solid-state alternative that eliminates solidification, thereby reducing the risk of microcracking. However, there is currently a lack of understanding between the interrelationship of process conditions, microstructure, and mechanical properties for IN625 produced by MEAM. This study investigates the influence of sintering time, 5 mins (short time) versus 4 hrs (long time) at 1290 °C, on the densification, microstructure, and mechanical performance of MEAM-processed IN 625. The 4 hrs sintered sample achieved a higher relative density (99.5%) compared to the 5 mins sample (98.5%), and both developed (Nb+Mo) rich carbides with distinct morphologies and volume fractions. Extended sintering reduced residual porosity, resulting in improved tensile strength and elongation. Fractographic analysis confirmed ductile failure via microvoid coalescence in both cases. These findings underscore the critical role of sintering duration in optimising density; despite developing microstructure characteristics that should degrade mechanical properties at longer sintering times, the mechanical properties of the 4 hrs sample were superior to those of the 5 min sample, revealing reduction of porosity to be the critical mechanism for maximising mechanical properties for this alloy and process.