ORCID Identifier(s)

0009-0000-1144-9434

Graduation Semester and Year

2023

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Narges Shayesteh

Abstract

ABSTRACT: Over the past five decades, Nickel-based and Titanium-based alloys have become increasingly popular materials. As the manufacturing industry for these alloys has advanced, the demand for fabricating complex parts with enhanced mechanical properties at elevated temperatures has grown. Laser Powder Bed Fusion (LPBF), one of the most prevalent additive manufacturing techniques, has been employed successfully to produce these alloys. Nonetheless, there is still considerable effort being made to improve the microstructural, compositional, and mechanical properties of LPBF-processed components. In this study, we focused on adjusting the multi-scale microstructure and composition of LPBF-fabricated Nickel-based and Titanium-based alloys. The first objective of this study was to investigate the spatial variation of microstructure, composition, and metallurgical properties in LPBF-fabricated samples. Our findings revealed that the properties of LPBF-processed parts vary across different heat-affected areas due to differences in heat transfer modes. To regulate the cooling rate, we fabricated cubic samples surrounded by cubic borders in the second study. The results showed deeper melt pools in the samples fabricated with borders compared to those without. Additionally, we observed a lower level of porosity and higher hardness values in the samples surrounded by borders. In the third study, we aimed to find the optimal gap value between the main sample and the border by considering a wide range of gap values. According to our findings, the smallest gap value resulted in a more homogeneous microstructure, increased ductility, and greater tensile strength. Furthermore, we achieved in-situ microstructure adjustment through martensitic decomposition for the samples fabricated with borders. The method used in this study proved to be capable of expanding the possibilities for in-situ property optimization of LPBF-processed products, presenting an alternative solution to post-processing techniques.

Keywords

Laser powder bed fusion, Additive manufacturing, Nickel-based alloys, Titanium-based alloys, Microstructure homogeneity, Mechanical properties, Border design

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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