Electronic Theses and Dissertations

Date

2022

Document Type

Thesis (Access Restricted)

Degree Name

Master of Science

Department

Mechanical Engineering

Committee Chair

Amir Hadadzadeh

Committee Member

Gladius Lewis

Committee Member

Reza Molaei

Abstract

A comparative study of the kinetics of precipitation and austenite reversion phase transformations in arc-directed energy deposition (arc-DED) and laser powder bed fusion (L-PBF) PH13-8Mo stainless steel is performed. During non-isothermal transformations, the materials are analyzed using differential scanning calorimetry (DSC) to determine the fraction of transformed precipitates and reverted austenite. To model the phase transformed volume fraction during precipitation and austenite reversion, the Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetic equation is employed. Based on the developed models, the nucleation and growth of the phases are interpreted according to the local Avrami index. The non-isothermal phase transformation kinetics model is utilized to develop the isothermal kinetics model. To enhance the hardness and strength of both arc-DED-PH13-8Mo and L-PBF-PH13-8Mo steels, the isothermal kinetics modeling results are used to design and develop aging heat treatments. Using optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), the microstructure of heat-treated materials were investigated. The microstructures were then correlated to the quasi-static mechanical properties (i.e. strength and ductility). This study provides insight into the phase transformation kinetics of the alloy and its importance in determining the desired heat treatment conditions for arc-DED and L-PBF samples.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest

Notes

No Access

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