Date of Award

Fall 2021

Project Type

Dissertation

College or School

CEPS

Program or Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Marko Knezevic

Second Advisor

Vera Popovich

Abstract

In this thesis, the mechanical behavior of the additively manufactured (AM) IN718 nickel-based superalloy and their correlations with the evolution of microstructure are studied comprehensively. The effects of manufacturing parameters, build orientations, and post processing procedures, i.e. standard heat treatment and hot isostatic pressing (HIP), on various mechanical properties including monotonic compression and tension strength, low cyclic fatigue performance, high cyclic fatigue behaviour, and fatigue crack growth behavior are investigated. Due to the high temperature applications of the IN718 alloy, elevated temperature properties are examined as well. Electron Backscattered Diffraction (EBSD) technique is employed to measure the initial and deformed textures. In addition, an elasto-plastic self-consistent polycrystal plasticity model is developed to interpret the deformation behavior of the alloy in room temperature and high temperatures. The model incorporates the contributions of solid solution, precipitates shearing, and grain size and shape effects into the initial slip resistance. For activating the slip systems, the non-Schmid effects and backstress are implemented in the model. The crystal plasticity model is capable of simulating the monotonic and large-strain load reversal cycles of the material with pole figure difference (PFD) values no more than 0.2.

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