Solution Anneal Heat Treatment to Enhance Mechanical Performance of Additively Manufactured IN718
Technical Report,01 Sep 2016,26 Mar 2020
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB United States
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Nickel-based superalloy IN718 is an excellent alloy for AM via LPBF. As-built LPBF IN718 has a vertically aligned, columnar microstructure which translates into orthotropic mechanical behavior. Post-process heat treatments for IN718 were developed 60 years ago for wrought processes and do not mitigate the microstructure of AM processes. Recrystallization is required to remove the columnar microstructure. This research investigated the evolution of LPBF IN718 microstructure under a recrystallizing solution treatment of 1160 deg C. It was shown that this higher temperature mitigated the anisotropy resulting from the fabrication process. Grain size and recrystallization were evaluated throughout the evolution. The XY and XZ planes were compared to find the point in time at which the annealing process produced equiaxed, isotropic grains. An equiaxed microstructure was successfully achieved through recrystallization and grain growth. Isotropic tensile properties were achieved with a recrystallization treatment of 1160 deg C for 4 hours and validated via tensile testing. Microstructural evolution was simulated in a kinetic Monte Carlo model using a novel approach of combining stored and boundary energies of the as-built LPBF IN718 with pinning particles. The models accurately approximated the experimental results of recrystallization and JMAK model constants.
- Metallurgy and Metallography