Thesis
Phase content influence on fracture properties of group VB transition metal carbides
Master of Science (M.S.), Drexel University
May 2018
DOI:
https://doi.org/10.17918/kbbz-3148
Abstract
Tantalum and other group VB transition metal carbides comprise of a class of ultra-high temperature ceramics (UHTCs) that are of particular use in machining tools and fuel-cladding on nuclear reactors. These material microstructures are controlled by the co-precipitation of metal-rich carbide phases, which in turn vary the mechanical properties based on the phase content. The major consideration in the use of UHTCs is their inherent brittleness, and currently little is known about their mechanical behavior in regards to varying microstructures and phase content, especially in niobium carbides. This thesis explores the flexural and fracture properties of two types of group VB transition metal UHTCs: tantalum carbide of carbon/tantalum (C/Ta) ratio in 0.5, 0.75 and 1.0, and niobium carbide of carbon/niobium (C/Nb) composition of 0.5, 0.67, 0.75 and 1.0. It is hypothesized that because of the carbon ratio, a second acicular shape phase will precipitate and ultimately increase the fracture toughness of the material. To explore the validity of the proposed hypothesis, x-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to identify the phase content and microstructure of the carbides, followed by three-point bend experiments using the surface crack in flexure (SCF) method on a universal load frame to determine the fracture properties. Various pre-cracking methods were explored which have been shown to influence the overall fracture toughness, and will be discussed. In addition, digital image correlation (DIC), a full-field identification technique, was used to examine in-situ deformations and resulting strains during loading. Overall, precipitation of metal-rich, acicular-shaped phase demonstrates a strong effect on the carbide fracture properties, and microstructural mechanisms responsible for various phase contents are discussed.
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Details
- Title
- Phase content influence on fracture properties of group VB transition metal carbides
- Creators
- Xingyuan Zhao - DU
- Contributors
- Leslie Lamberson (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Master of Science (M.S.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- ix, 52 pages
- Resource Type
- Thesis
- Language
- English
- Academic Unit
- College of Engineering (1970-2026); Mechanical Engineering (and Mechanics) (1970-2026); Drexel University
- Other Identifier
- 8311; 991014632082704721