High-Temperature Performance of UNS N07718 Processed by Additive Manufacturing Available to Purchase

The effect of processing, microstructure and composition on the oxidation behavior and mechanical properties of UNS⁽¹⁾ N07718 fabricated by additive manufacturing (AM) using the electron beam melting (EBM) process was evaluated and compared with properties of wrought UNS N07718. Material was evaluated in three conditions: 1) as-fabricated, 2) following hot isostatic pressing (HIP) and 3) following HIP and a standard 2-stage heat treatment. The EBM processing resulted in a texture in the build direction and the microstructure consists of three typical precipitates in each condition: L1₂ structured γ′ Ni₃(Al,Ti), disc-like DO₂₂ structured γ″ and δ-Ni₃Nb. Tensile properties were measured at room temperature and 650 °C. With only HIP, a lower yield stress and higher elongation were measured. However, the as-fabricated and HIP + heat treated conditions led to tensile properties that are comparable to wrought UNS N07718. Oxidation testing was performed in wet air and processing was shown to have little effect on the behavior at 650° and 700 °C for 1,000 h. Differences were observed in accelerated testing at 750 °C with a thicker oxide formed on the EBM UNS N07718. In general, the EBM processing appeared to have only minor effects on oxidation behavior.