Oxidation-Assisted Cracking at 650 °C in Superalloy 718 Manufactured by Laser Beam Melting: Effect of Temperature and Strain Rate

Additive manufacturing of complex parts in superalloy 718 by Laser Beam Melting (LBM, also referred to Selective Laser Melting, SLM) is currently under the evaluation by the aerospace industry, due to the opportunity to combine alloy 718 excellent properties and versatility of use, with the benefits and increasing maturity of LBM technology. In this work, the interactions between fracture modes and deformation modes for LBM-manufactured 718 were studied at 20, 450 and 650 °C. Vertical and horizontal tensile specimens were fabricated, then heat-treated with two sets of standard solution-aging treatments, before being tested in air over a range of strain rate from 8 × 10^–5 to 3 × 10⁻² s⁻¹. Results of these tests showed evidence of a coupling effect between oxidation and mechanical loading, resulting in oxidation-assisted cracking of LBM 718 alloy for the same temperature and strain rate conditions than conventionally-manufactured alloy 718. Also, in spite of consisting of fundamentally different microstructures, relationships between fracture modes and deformation modes for laser beam melted 718 were found to be surprisingly consistent with the ones previously established for conventional 718. These results suggests that microstructure parameters such as grain size and morphology, or phase distribution are not involved at the first order in the mechanisms controlling these interactions. To further describe these phenomena, the interactions between solute elements, mobile dislocations and interfaces must be considered.