On the Development of a Heat Treatment for Inconel Alloy X-750 Produced Using Laser Powder Bed Fusion

Abstract

The substantial development that the additive manufacturing technique of powder bed fusion using a laser beam (PBF-LB) underwent in the past decades, though expressive, has been restricted to particular materials and applications. When coming to Ni-based superalloys, the technology has been mostly developed regarding a few polycrystalline Ni–Cr–Fe and Ni–Cr alloys, particularly Inconel 718 and 625. However, when produced using PBF-LB, these materials should undergo tailored heat treatment sequences to adjust its microstructure to industrial standards, which must be developed according to the behavior of each particular alloy. In view of such restrictiveness, this study assessed 77 experimental heat treatments for PBF-LB Inconel X-750, an alloy with comparatively limited research volume when considering additive manufacturing, aiming at providing guidelines for its post-processing after PBF-LB manufacturing. These heat treatments were based on the standard ASM 5668 sequence for maximization of creep resistance, and, contradicting the known precipitation behavior of the conventional material, often resulted in coarse precipitation of detrimental bulk η-Ni₃Ti intermetallic phases. This indicates insufficient chemical homogenization after heat treatment, evidencing a different microstructural response of the material when processed using PBF-LB and the importance of optimizing the post-processing of such materials.