Out-of-Equilibrium Formation of Ni3Ti η-Phase in Inconel X-750 Produced via Laser Powder Bed Fusion and Spark Plasma Sintering

Advanced manufacturing techniques such as powder bed fusion of metals using a laser beam (PBF-LB/M) and spark plasma sintering (SPS) for the production of superalloy components can potentially become competitive with the industry-established routes of casting and forging. In contrast with those routes, these novel methods are particularly effective in optimizing component geometry, which is not so easily accomplished when using conventional techniques. However, since the manufacturing conditions imposed by such methods are considerably different from those of casting and forging, the final microstructure of the materials produced may vary. This is described in the present study with regard to a γ′-strengthened Ni-based superalloy produced through PBF-LB/M and SPS, production routes which, after heat treatment, induced the formation of acicular η-Ni3Ti within the alloy’s microstructure. This phase was identified at grain boundaries of both materials, not being expected according to the heat treatment employed. Such distribution, which contrasts with reports from the literature, is expected to lead to the impairment of the mechanical behavior of the materials produced using these techniques, a prospect that is supported by nanoindentation measurements of local hardness and stiffness.