Masters Theses
Keywords and Phrases
Alloy design; High-strength low-alloy steel; Laser-directed energy deposition; Powder blend; Robustness; Sensitivity analysis
Abstract
"To ensure consistent quality of additively manufactured parts, it is advantageous to identify alloys which can meet performance criteria while being robust to process variations. Toward this end, this work investigated the effect of alloy composition on the robustness of steels consolidated via laser-directed energy deposition (L-DED). Ultra-high-strength low-alloy steel (UHSLA) and pure iron powders were mixed in-situ to produce 10 compositions containing 10-100% UHSLA by mass. JMatPro material simulations roughly predicted phases and mechanical properties. Two sets of experiments were used to evaluate the sensitivity of as-built hardness (all 10 compositions) and tensile properties (5 select compositions) to process parameters. The hardness sensitivity peaked at 40-50% UHSLA, corresponding to phase fluctuations between lath martensite and upper bainite depending on the cooling rate. Lower (≤20%) or higher (≥70%) alloy contents were generally less sensitive, transforming primarily to ferrite or martensite, respectively, with auto-tempering of martensite at lower cooling rates. The ultimate tensile strength (UTS) and yield strength (YS) sensitivities followed a similar trend up to 70% UHSLA, beyond which the YS sensitivity remained low while the UTS sensitivity increased, corresponding to variations in the work hardening behavior. This may reveal that the work hardening capability at higher alloy contents is particularly sensitive to factors such as auto-tempering and/or grain size. A robust compositional balance (70%) avoided martensite/bainite fluctuations while minimizing other microstructural sensitivities. The 70% mixture also represented a minimum alloy content at which ductility could be improved without sacrificing tensile toughness. While its high strength (UTS 1,296 MPa) was lower than that of UHSLA (UTS 1,632 MPa), its improved elongation (21.7%) over UHSLA (16.9%) caused its tensile toughness to about match that of UHSLA. This work demonstrates the efficacy of a methodology for incorporating robust design into the rapid evaluation of alloys for metal additive manufacturing"--Abstract, p. iii
Advisor(s)
Liou, Frank W.
Committee Member(s)
Newkirk, Joseph William
Leu, M. C. (Ming-Chuan)
Department(s)
Mechanical and Aerospace Engineering
Degree Name
M.S. in Manufacturing Engineering
Publisher
Missouri University of Science and Technology
Publication Date
Spring 2025
Pagination
xii, 127 pages
Note about bibliography
Includes_bibliographical_references_(pages 120-126)
Rights
©2023 Jonathan Kelley , All Rights Reserved
Document Type
Thesis - Open Access
File Type
text
Language
English
Thesis Number
T 12485
Recommended Citation
Kelley, Jonathan, "Influence of Alloy Composition on the Process Robustness of Steels Consolidated Via Laser-Directed Energy Deposition" (2025). Masters Theses. 8240.
https://scholarsmine.mst.edu/masters_theses/8240
