Date of Award

2017-01-01

Degree Name

Doctor of Philosophy

Department

Material Science and Engineering

Advisor(s)

Dr. Ryan B. Wicker

Abstract

Additive manufacturing (AM), or layer-by-layer part fabrication, is enabling the materialization of ideas that were near to impossible to achieve in the past, while providing advantages that include reduced material footprint, increased complexity, reduced lead times, etc. AM has been integrated to highly specialized markets that include aerospace, military, automotive, biomedical, and prototyping.

Although an apparent growth is being witnessed across nearly all AM platforms, technologies with capabilities of producing metallic parts have arguably received the most widespread interest, with powder bed fusion (i.e. electron beam melting and selective laser melting). This class of AM technology produces parts by judiciously melting precursor powder, represents 90% of the metal market [1]. Binder jetting, although not categorized under powder bed fusion, is also a powder bed-based technique that can be used for direct metal fabrication, and that is seeing an increased adoption in low-cost applications, such as metal prototypes. As these technologies continue to evolve, more industries are implementing to production.

A limited amount of comparative studies exists between powder bed-based AM technologies for the fabrication of metallic components that include initial fabrication steps and continue to final end-user production. This research includes an extensive characterization and comparison between commonly used powder bed-based AM technologies including (1) electron beam melting (EBM), (2) selective laser melting (SLM), and (3) binder jetting. The aim of this research is to have a thorough examination of the AM techniques by evaluating advantages and constraints faced by each technology by the fabrication of metallic components. The study contains an evaluation on system cost, fabrication time for parts, energy consumption during fabrication, mechanical properties, as well as fractography. By creating a comparative study that provides insight into the fabrication process and characterizes each technology's product, possible applications and capabilities of each technology for meeting the demands of the application is gained. This study can be used to determine distinct characteristics between the three listed technologies and followed for other technologies and materials using similar approaches.

First, an analysis considering the fabrication time and energy consumption of producing parts for all three platforms was conducted. Results determined that SLM technology required the least amount of fabrication time and energy for the fabrication of single part fabrication. However, for production of multiple parts, or large volume builds, binder jetting technology becomes an efficient form of fabrication method.

Subsequently, the study continued with characterization of Inconel 625 fabricated by the three powder bed-based technologies in the X and Z build orientations. Metallography revealed directional microstructure dependence for EBM fabricated specimens that remained after a hot-isostatic pressing (HIPing) process. However, the melt pools found in the microstructure of SLM fabricated specimens were removed once HIPed, leaving a more homogenous microstructure. Observations made for binder jetting microstructure were larger grains in comparison to EBM and SLM. SLM outperformed both technologies in the mechanical properties tested (i.e. ultimate tensile stress, % elongation, yield stress, and modulus of elasticity) with nearly all technologies able to surpass the minimum requirements based by ASTM-F3056-15 a standard for AM fabrication parts similar to wrought Inconel 625. Both EBM and binder jetting were unsuccessful in achieving the minimum standard in % elongation (at break). All specimens demonstrated a ductile fracture mode, exposed in the form of dimple formation on fracture surfaces, after performance of failure analysis.

The final aspect of this research investigated the fabrication of "smart parts" employing an interrupted process that allowed embedding sensors in AM produced parts during the build process. It was demonstrated that the layer-by-layer part fabrication of AM, enables the opportunity of fabricating "smart" complex components by allowing the insertion of a piezoceramic sensor during a multi-step "stop-and-go" process that can only be achieved by an additive manufacturing method.

Language

en

Provenance

Received from ProQuest

File Size

141 pages

File Format

application/pdf

Rights Holder

Jose Angel Gonzalez

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