Date of Award

3-2021

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Ryan A. Kemnitz, PhD

Abstract

Additively Manufactured tungsten suffers from low () densities due to high concentrations of microcracks as the printed layers cool past tungsten's high ductile to brittle transition temperature. In this study, tungsten-rhenium and tungsten rhenium hafnium carbide compositions were evaluated on density and tensile strength. In addition to varying the compositions of each alloy, printing parameters and post-processing methods were also compared. Print parameters varied for all compositions on an MLab 200R C using included the laser scan strategy, hatch spacing, scan speed, laser power, and print bed material. Post processing techniques of the WRe compositions included hot isostatic pressing and hydrogen annealing treatments. In particular, two combinations achieved high density (>97 ) indicating a reduction in micro-cracking: W25Re which underwent H annealing, and W25Re1HfC as-printed. In both cases the mechanism was likely oxygen impurities being scavenged, either by hydrogen or carbon. The H annealed W25Re tensile bar achieved a 701 MPa room temperature ultimate tensile strength. Scanning Electron Microscope images of the annealed W25Re and the as-printed W25Re1HfC show no microcracks. This was further confirmed on the W25Re1HfC using Focused Ion Beam imaging techniques. However, the reduction in microcracking in the latter led to a buildup in thermal stresses during printing, causing both lifting from the print bed, and macro sized cracks through the printed part approximately every 5mm in print height. Lifting was reduced by using a copper build plate, with an "island" laser scan strategy.

AFIT Designator

AFIT-ENY-MS-21-M-299

DTIC Accession Number

AD1139786

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