Date of Award

Spring 2023

Access Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Alberto Mello

First Committee Member

Sirish Namilae

Second Committee Member

Daewon Kim

College Dean

James Gregory

Abstract

Nickel-based superalloys are used extensively in the aviation industry, particularly in aircraft engine components. These materials are desirable due to their high strength, resistance to creep, corrosive environment, and high temperature. It has been well documented that material fatigue is characterized by material microstructure, type of loading, and other parameters. Currently, research into the effects of fatigue on complex materials like nickel-based superalloys is being pursued. Previous research has found that preconditioning of Inconel 718 samples at 700 ℃ with 1.0% strain led to an improved fatigue life. It has been suggested that this could be caused by the activation of the {100} cubic slip plane along the usual {111} octahedral slip plane. This study continued the work of previous research by using SEM and EBSD imaging to characterize the microstructure of IN-718 specimens before and after preconditioning. The microstructure grains and their orientations before preconditioning were found for a distinct area of interest using EBSD. Following the preconditioning, the same study area was found and activity inside the grains were monitored. Following preconditioning, some grains exhibited bidirectional slip bands while others exhibit unidirectional. Characterizing these slip bands showed that some resided in the {111} system while others, particularly the bidirectional slip bands, resided in the {100} direction. This confirms that the preconditioning caused the activation of the cubic slip system. As such, this favorable change in the microstructural better accommodates the applied stress and reduces the strain localization, leading to the improved fatigue life. Future research can be conducted in-situ by using a special frame and heater inside the microscope chamber. This will allow monitoring engineering strain and slip band formations as heat and load are applied. Such equipment is not available at the moment, but is part of the equipment development proposal of the ERAU Aerospace Material Research Group.

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