Date of Award

9-2022

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Ryan A. Kemnitz, PhD

Abstract

This research considered additive manufactured (AM) molybdenum (Mo) and the effect of three variables on microstructure, mechanical properties, and the relationship between the two. Test temperature, laser speed, and shield gas or build atmosphere were varied, and samples tested and analyzed using a three-point bending test, chemical composition, and optical and scanning electron microscopy. The relationship among variables and results using a Design of Experiments was limited compared to the inclusion of every tested sample. Most effects were expected: samples tested at room temperature were brittle without statistical significance; increasing laser speed resulted in decreased ductility and strain, smaller grain sizes, and increased quantity of grains; and percentage of hydrogen in the shield gas had very little effect compared to the other variables. Nitrogen was preferable to an argon shield gas, results showing both higher stresses and strains under the same conditions. Stress followed expectations given oxygen content, keyhole porosity, and un-sintered materials. Maximum stress occurred at an intermediate laser speed and volumetric energy density (VED). Despite resulting porosity, nitrogen as a shield gas shows promise in AM fully dense Mo. Heat treatments and adjusting VED contribute to producing fully dense Mo and should be considered in future work.

AFIT Designator

AFIT-ENY-MS-22-S-111

DTIC Accession Number

AD1183240

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