Degree

Doctor of Philosophy (PhD)

Department

Mechanical and Industrial Engineering

Document Type

Dissertation

Abstract

Additive manufacturing (AM) is a rapid prototyping technology to produce fully functional and complex designing objects. As one of the AM methods, Laser Powder Bed Fusion (LPBF) has gained the most attention from both academic researchers and industrial companies. During the LPBF process, metal powders are applied layer by layer, which can be 20 microns to 50 microns in thickness. After a layer is prepared, a high-power laser, which is commonly controlled by a scanning head, is used to selectively melt the interested area of a 2D geometry which is designed in a computer aided designing software. LPBF method can be described as a repetitive welding process that is rescaled into micron dimension level. The melting track is called melting pool in this additive manufacturing method. The dimension of the horizontal cross section of a melting pool in LPBF is around 100 μm by 100 μm. The present research studied AM samples prepared using a variety of metal alloys, including stainless steel 316L (SS316L), titanium alloy (Ti-6Al-4V), and high entropy alloy (HEA), which are all prepared by the LPBF method. Tensile and fatigue tests are conducted on multiple groups of SS316L samples to reveal the mechanical properties which are also compared with the samples prepared in conventional fabrication methods. Nondestructive evaluation methods, like positron annihilation lifetime measurements and neutron interferometry detection, are used to detect the changes of defects inside the as-printed and post-treated samples. The high entropy alloy (HEA), AlCoCrFeNi, is studied by in-situ synchrotron X-ray diffraction (XRD) technique, together with the methods of conventional XRD and scanning electron microscope (SEM). In the final chapter, titanium alloy (Ti6Al4V) dental implants produced by LPBF method are studied together with a biomedical team of Dr. Shaomian Yao.

Date

7-9-2021

Committee Chair

Guo, Shengmin

Available for download on Saturday, July 06, 2024

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