Effect of microstructure in electrospark deposition repaired conventional and additive manufactured Ni-superalloys
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Date
2021-04-23
Authors
Enrique, Pablo D.
Journal Title
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Publisher
University of Waterloo
Abstract
The ability to extend component lifespans and improve performance through repair and coating techniques is an important area of research with widespread industrial applications. Numerous industries, including aerospace, can benefit significantly from advancements in the repair and coating of high-performance, heat-sensitive parts; with engine temperatures steadily increasing and the shift towards reusable space exploration vehicles in cargo and crewed flights, the durability of key components is a concern. This is especially true with the increasing use of additive manufacturing, which can create parts with considerable geometrical freedom but suffer from high surface roughness and near-surface porosities.
Electrospark deposition (ESD) is a promising choice for the repair and coating of sensitive components due to its low heat input. When alloys are processed using ESD, a very fine subgrain microstructure forms with the potential for micro-segregation at subgrain boundaries. The aim of this research is to identify the influence of the subgrain microstructure and subgrain boundaries on the mechanical properties and phase transformations in Inconel 718, a commonly used Nb-rich Ni-superalloy. Inconel 718 is deposited on conventional Inconel 718 substrates in a series of studies that evaluate the ability to repair cavities and apply coatings. The included studies relate the thickness of solidified droplets (splats) to the size of the subgrain microstructure, microhardness, and yield strength of the material, while demonstrating that the subgrain and splat boundaries act as crack propagation pathways during tensile failure. Micro-segregation of Nb along the subgrain boundaries is also shown to increase the number of Nb-rich phases forming during high temperature heat treatments. These studies improve our understanding of the mechanical response of ESD-processed Nb-rich Ni-superalloys, and are used to tailor the application of ESD to improving the surface condition and fatigue life of a dissimilar additive manufactured Ni-superalloy. The findings show potential for the repair and surface enhancement of damaged or critical regions in heat-sensitive conventional and additive manufactured parts.
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Keywords
electrospark deposition, Ni-superalloys, additive manufacturing, surface post-processing, coatings, repairs, microstructure