Mechanical performance of as-built and heat-treated Inconel 625 additively manufactured by L-DED with different build orientations

Abstract

Additive manufacturing of the Ni-based Inconel 625 superalloy, as an alternative to conventional methods, is of interest to produce near-net-shape parts, due to this alloy's intrinsic high abrasiveness and poor machinability. Because of the complex thermal history of L-DED AM, post processing heat-treatments are often required for stress relief and microstructure homogenization. This work investigates the mechanical performance of Inconel 625 specimens manufactured by laser directed energy deposition (L-DED) in the as-built and heat-treated conditions (900 °C for 2 h). Microstructure was characterized by optical and scanning electron microscopy with energy dispersive spectroscopy. Mechanical properties were assessed by Vickers hardness, tensile, and Charpy impact tests. The effects of build orientation and heat-treatment were discussed, and results were benchmarked to those of commercial Inconel 625 reported in the literature. Results show that the as-built samples developed a columnar dendritic microstructure with epitaxial grain growth, and the presence of Mo, Nb, and Si-rich interdendritic Laves phase. The post processing heat-treatment led to partial recrystallization and formation of Laves phase and carbides at grain boundaries, which caused a Charpy energy absorption reduction of about 40 % compared with the as-built condition. This behavior was similar to that observed for the wrought Inconel 625. Under tensile solicitations, the grain boundary embrittlement decreased the total elongation but did not compromise yield strength and ultimate tensile strength, which remained superior to those expected from Ni–Cr–Mo–Nb alloys, as reported by ASTM B446-24. Slightly superior hardness, yield strength, and ultimate tensile strength were found for horizontally built specimens. This outcome is associated with its higher cooling rates and microstructure refinement.

Keywords

• Ni-based alloy
• Laser metal deposition
• Annealing embrittlement
• Grain boundary embrittlement
• Toughness