Influence of heat treatment on the high temperature properties of Inconel 718 fabricated via Laser Beam Powder Bed Fusion

This study investigates the influence of post-manufacture heat treatments on the high-temperature performance of Inconel 718 produced via Laser Beam Powder Bed Fusion (LB-PBF). Two industrially relevant heat treatment routes were explored: one optimised for low cycle fatigue (HT1) and the other for creep resistance (HT2), and their effects were compared against as-received (AR) LB-PBF and conventionally wrought IN718. Mechanical testing, including tensile, constant load creep, and strain-controlled low cycle fatigue (LCF) at 650 °C, was complemented by extensive microstructural characterisation via EBSD, SEM, and EDX. HT1 exhibited a significantly refined microstructure, enhanced twin density, and promoted fine, well-distributed secondary phases, resulting in superior fatigue performance and creep resistance comparable to wrought material. HT2, while enhancing tensile strength and hardness relative to AR, offered limited improvement in creep resistance. All LB-PBF variants exhibited lower ductility and more heterogeneous dynamic strain aging (DSA) behaviour than the wrought alloy. The study demonstrates that tailored heat treatments can enhance the high-temperature mechanical performance of LB-PBF IN718, with HT1 identified as the most effective approach for fatigue-critical applications.