Term of Award

Spring 2025

Degree Name

Master of Science, Mechanical Engineering

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Mechanical Engineering

Committee Chair

Dr. Bishal Silwal

Committee Member 1

Dr. Hossein Taheri

Committee Member 2

Mohammadamin Ezazi

Abstract

Wire arc additive manufacturing is a process well suited to the efficient production of large structures. Duplex stainless steel exhibits high corrosion resistance and good strength which can be highly beneficial for industrial use. However, its use is limited due to its cost and complexity in controlling microstructure to achieve desired properties. In many cases, it can be highly beneficial to manufacture a component which uses specialty steel grades such as duplex stainless steel only where necessary, and utilizes more affordable, commonly available steels for reinforcement or bulk structural support. A functionally graded material satisfies these requirements by providing a gradient of material properties within a part allowing for localized specification of properties. A functionally graded structure is fabricated using pulsed wire arc additive manufacturing to highlight the capabilities of such a material and provide a basis for construction of very large scale functionally graded components. This is accomplished by layering duplex stainless steel (ER2209, DSS2205 equivalent) on top of high strength low alloy steel (LA-100, HSLA-100 equivalent). Parameter optimization studies are performed to determine optimal printing parameters of each material and the proper layer ordering for the material combination. After FGM fabrication, mixing of the constituents was observed in many locations at the heterogeneous material interface. No obvious brittle intermetallic compounds were observed in the mixed material. Above the interface, samples taken from ER2209 exhibited a high fraction of austenite, with the ferrite fraction increasing away from the weld interface. Below the interface, LA100 microstructure consisted of martensite and bainite structures. Microhardness testing revealed ER2209 had a higher hardness than the LA100, with the highest average hardness (332.65HV) observed at the immediate interface. Five tensile samples were tested with each sample fracturing in a nearly identical (within ~1mm) location. Digital image correlation of the tensile tests revealed small stress concentrations at the FGM interface that were not deleterious to the strength of the material (σy=524.733±5.64 MPa, UTS=685.028±3.22 MPa, ϵ=18.4%). Fractographic observation revealed failure in the LA100 due to microvoid coalescence with most voids originating from inclusions. Fracture in the samples may have been influenced by large inclusions observed at the fractured surface.

OCLC Number

1520503824

Research Data and Supplementary Material

No

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