Date on Master's Thesis/Doctoral Dissertation

12-2013

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Industrial Engineering

Committee Chair

Stucker, Brent E.

Author's Keywords

Additive manufacturing; Defect; Selective laser melting; Titanium alloy; Electron beam melting

Subject

Electron beam welding; Quality control; Lasers--Industrial applications

Abstract

Application of Additive Manufacturing (AM) technology to fabricate complex three-dimensional components is one promising direction within the manufacturing industry. This approach is rapidly changing the way designers and engineers create objects with desired shape and structures. Selective Laser Melting (SLM) and Electron Beam Melting (EBM) are two common powder bed fusion processes within AM for fabricating metallic parts. In order to give designers and engineers more insights into employing AM, the quality and long-term behavior of SLM- and EBM-produced parts need to be carefully investigated. Thus, this research project aims to understand how processing parameters affect defect generation and distribution during SLM and EBM processes, to study the morphological features of defects, to identify effective non-destructive method(s) to detect these defects, and to characterize the effect of defects on mechanical properties of SLM- and EBM-produced parts. The study began by generating stochastic defects via adjustment to process parameters from optimal parameters to marginal parameters, in order to correlate the porosity to the marginal parameters. Archimedes method was employed to estimate porosity of SLM- and EBM-produced specimens. After this, by using destructive characterization techniques, the defective specimens were sectioned. The morphology of stochastic defects was investigated based on their contour features on the cross sections. Micro CT was primarily used to evaluate the stochastic defects in the SLM and EBM parts and demonstrate their morphological characteristics and porosity in the single slices and reconstructed models. Finally, tensile and fatigue tests were carried out on Ti-6Al-4V parts with identified porosity. The fracture mechanism was analyzed. This study established a fundamental understanding of defects in parts made by SLM and EBM processes. Porosity was quantitatively correlated to the marginal parameters of SLM and EBM processes. Defects were differentiated based on their morphological properties and features. Micro CT was confirmed to be an effective non-destructive method for evaluating stochastic defects in SLM- and EBM-produced parts. The effects of stochastic defects on Ti-6Al-4V parts were determined based on tensile and fatigue tests. It was found that both microstructure and porosity have an impact on the mechanical properties of SLM- and EBM-produced parts.

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