Doctoral Dissertations

Abstract

Laser powder bed fusion (LPBF) is a metal additive manufacturing method that produces non-traditional microstructures as a result of the rapid solidification and thermal cycling inherent to the process. When using LPBF-produced material in application, these unique microstructures challenge the applicability of well-developed mechanical property databases achieved by conventional heat treatments. For wider adoption of this technology, a more holistic understanding is necessary on how process attributes develop material structure, which dictate mechanical properties. This dissertation explores the process structure-property relationships in LPBF 17-4 PH steel through systematic evaluation of atmospheric processing and heat treatment effects on microstructure and mechanical performance. Specimens were fabricated under controlled build environments, subjected to a range of solutionizing, homogenizing, and aging treatments, and characterized using optical microscopy, electron back scatter diffraction (EBSD), and X-ray diffraction (XRD) to quantify phase evolution. Tensile testing was performed to directly link heat treatment pathway and nitrogen absorption to mechanical performance. This work demonstrates where conventional heat treatment standards are applicable to LPBF 17-4 PH steel and where modifications are required. By directly correlating phase stability, nitrogen effects, and tensile response, this work provides practical guidelines for tailoring post-processing strategies. These findings underscore that successful application of LPBF 17-4 PH steel requires explicit consideration of both build environment and post-processing. By linking processing conditions to microstructure and performance, this work advances understanding of critical variables that govern reliability of additively manufactured precipitation-hardened stainless steels in demanding applications.

Advisor(s)

Liou, Frank W.

Committee Member(s)

Park, Jonghyun
Newkirk, Joseph William
Leu, M. C. (Ming-Chuan)
O'Malley, Ronald J.

Department(s)

Mechanical and Aerospace Engineering

Degree Name

Ph. D. in Mechanical Engineering

Publisher

Missouri University of Science and Technology

Publication Date

Fall 2025

Journal article titles appearing in thesis/dissertation

Paper I: Pages 7-42,” Atmosphere Effects in Laser Powder Bed Fusion: A Review” has been published in Materials.

Paper II: Pages 43-65,” Absorption of Nitrogen during Pulsed Wave LPBF of 17-4 PH Steel” has been published in Materials.

Paper III: Pages 66-88,” Tensile Performance Sensitivity to Variations of Standard 17-4 PH Steel Heat Treatments on LPBF Produced Material” has been published in Metals.

Pagination

xii, 93 pages

Note about bibliography

Includes_bibliographical_references_(pages 91-92)

Rights

© 2025 Ben Brown , All Rights Reserved

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 12558

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