Date of Award

2021-12-01

Degree Name

Master of Science

Department

Mechanical Engineering

Advisor(s)

Francisco Medina

Abstract

Pure tungsten is a refractory metal and has been gaining interest for the use in nuclear fusion reactors as a plasma facing material. Titanium Aluminide (TiAl) has been growing in popularity as a possibly to phase out Nickel based superalloys due to its high specific strength at elevated temperatures. These two materials suffer from poor machinability due to being brittle at room temperature. Additive manufacturing (AM) is a recently developed manufacturing method that is fundamentally different than formative or subtractive. AM is a layer-by-layer process that has the potential to manufacture metals to a near net shape. Since the AM process is highly variable, the process and resulting material properties need to be verified. The goal of this thesis was to understand the machine parameters that allows processing of these materials. Tungsten is in an early developmental phase; the goal was to find processing parameters that would yield fully dense tungsten. The build substrate and support structures are critical in the production of the final part. Energy densities greater than 370 J/mm3 led to ~98% relative density of pure tungsten. Regarding TiAl, the “as built” condition suffers from anisotropy or heterogeneity in the microstructure, so post processing is highly recommended. The TiAl underwent Hot Isostatic Pressing (HIP) and heat treatment to improve the “as built” parameters. Metallography and tensile tests were completed to determine the mechanical properties. The cooling rate of 5°C/min caused the resulting microstructure to be similar with similar mechanical properties. The microstructure was nearly fully lamellar which had around 380 MPa yield stress and around 410 MPa ultimate tensile stress. The elongation was less than 1%. These experiments lay the groundwork for future manufacturing of brittle materials using electron beam powder bed fusion technology. This proves that this can be an effective method of manufacturing to produce favorable material properties for use in their respective applications.

Language

en

Provenance

Recieved from ProQuest

File Size

101 p.

File Format

application/pdf

Rights Holder

Kurtis Isami Watanabe

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