Date of Award

Spring 2018

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Metallurgical Engineering

Committee Chair

KV Sudhakar

First Advisor

Bruce Madigan

Second Advisor

Ronda Coguill

Third Advisor

Brahmananda Pramanik

Abstract

Additive manufacturing using laser powder bed fusion (AM-LPBF) methods have recently experienced rapid growth and development, having the potential to replace manufacturing by plastic deformation, precision machining, or casting. AM offers advantages such as the freedom to design highly complex geometries, time and cost savings through material usage efficiency and shortened production cycles, and the potential for improved mechanical properties. Process induced defects, however, result in degradation and scattering of mechanical properties and hinder the widespread adoption of AM-LPBF in industry. This investigation focuses on the effects of varying energy density and build orientation on the evolution of process induced defects within an AlSi10Mg alloy produced using AM-LPBF. The area percentages and morphologies of the porosity is then related to the tensile and fatigue properties exhibited by the AlSi10Mg specimens. The area percentage of porosity within specimens was found to increase as the energy density of the build increased. The morphology of pores at higher energy densities also became more spherical in shape, suggesting excessive energy density caused the entrapment of gas bubbles within the melt. Lower energy densities resulted in a lower percentage of porosity although the general morphology of these pores appeared jagged or faceted in shape; likely resulting from lack-of-fusion defects during the build. Tensile properties including ultimate tensile strength (UTS) were found to increase as energy densities and resulting porosity decreased. Fatigue properties, however, were highest in specimens with the highest percentages of porosity despite having lower tensile strengths. This may derive from the spherical morphology of entrapped gas porosity within these specimens producing less of a stress concentration when compared to faceted lack-of-fusion porosity.

Comments

A thesis submitted in partial fulfillment of the requirements for the degree of Masters of Science in Metallurgical and Materials Engineering

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