Processing, microstructure, and mechanical properties of additively manufactured IN718 nickel-based superalloy
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Date
2024-10
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University of New Brunswick
Abstract
Inconel 718 (IN718) is a widely used superalloy in aerospace applications requiring high strength at elevated temperatures. This thesis comprehensively explores the processing, microstructure, and mechanical behavior of IN718 manufactured by wire arc additive manufacturing (WAAM) and via laser powder bed fusion (LPBF). First, WAAM-produced hybrid IN718-S275 components were investigated, examining interfacial characteristics and texture evolution. Notably, laves phase persistence was observed near the interface even after solution treatment. Neutron diffraction was used to validate the texture of the hybrid components where a strong texture parallel to the build direction in WAAM-IN718 was identified. Elastic-field models were utilized to understand dislocation mobility and Peierls-Nabarro stress, elucidating the role of heat treatment in modifying mechanical properties. Next, differential scanning calorimetry (DSC) was employed to optimize the solutionizing temperature for the complete dissolution of undesirable phases (δ and laves) in LPBF-IN718, with subsequent microstructural characterization. This led to the elimination of micro-segregation and significant Laves dissolution, resulting in a hardness comparable to wrought IN718 alloys. Furthermore, the dynamic deformation behavior of LPBF-IN718 was studied under various elevated strain rates. AMS 5664 heat treatment resulted in a remarkable 28% increase in ultimate compressive strength. Microstructural analysis revealed the presence of strengthening γ" and γ' phases in abundance, and high-density dislocation networks was observed. The influence of strain rate on grain size, texture, and adiabatic shear band formation was thoroughly investigated. The research presented in this thesis provides a comprehensive understanding of how processing techniques and post-fabrication treatments influence the microstructure and mechanical behavior of IN718. This knowledge contributes to optimizing manufacturing processes and developing tailored IN718 heat treatments for aerospace applications. Additionally, this work offers valuable insights into the mechanical response of additively manufactured IN718 under high-strain-rate loading conditions, enhancing the understanding of its performance in critical aerospace and engineering applications.