Date of Award

Fall 2019

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Materials Science

Committee Chair

Sudhakar Vadiraja

First Advisor

Bruce Madigan

Second Advisor

Brahmananda Pramanik

Third Advisor

Lee Richards

Abstract

Additive Manufacturing (AM) is a technique to produce special products by depositing layers of material in a specific pattern. Wire and arc additive manufacturing (WAAM) is an AM technique that uses welding equipment that has been modified and automated to deposit layers of welding wire. Characterization of specimens produced by WAAM method is required to optimize the process parameters. This research focuses on the microstructure characterization of 308L stainless steel samples produced by a novel WAAM technique known as Plasma Arc Weld Print 3D (PP3D). PP3D consists of multiple plasma arc torches that can deposit material in two modes of deposition: a more conventional continuous deposition seen commonly in other WAAM techniques, and a “dabber” deposition mode that places small, overlapping weld beads. The PP3D technique and specially the “dabber” mode was developed with the intention to (1) reduce directional sensitivity of deposition and (2) refine microstructure to reduce the occurrence of large columnar grain structures. Characterization of the specimens produced by these two modes was carried out by metallographic imaging, micro- and macro-indentation testing, and fractography of the fractured sample surfaces from tensile testing. Dabber mode sub-grain features were considerably finer in size while being highly variable in orientation and morphology. This is in comparison to continuous mode samples which were coarser and more consistent in orientation. At the macro level, features of the dabber mode are consistently coarser with frequent columnar grain features when compared to the continuous deposition mode. Failure surface features are highly consistent with a ductile failure mode with many dimples with few inclusions. Further refinement of the deposition conditions and settings is likely to produce results more in line with the PP3D system’s objectives.

Comments

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Materials Science and Engineering

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