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Title: Deformation mechanisms in 6H silicon carbide : experimental and numerical analysis
Author: Pang, Ka-Ho
ISNI:       0000 0004 7970 9062
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2019
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This research aims at developing a fundamental understanding of the deformationmechanisms in single crystal 6H silicon carbide (6H-SiC). Owing to the continuous miniaturization of electronics devices, silicon carbide (SiC) continues to be of exceptional interest to the electronic industries. It is poised to replace silicon-based MEMS devices used in the most technically demanding environment due to its excellent bandgap characteristics, extreme hardness, high thermal conductivity, chemical inertness and wear resistivity. On the other hand, SiC can also be used as structural components in the aerospace, automotive and nuclear industries where components are subjected to high temperature, high power frequency or irradiated environments. Components from SiC can range from component dimensions as small as 0.1µm to the largest in the macroscopic scale with dimensions in centimetres. A good understanding of deformation behaviour is, therefore, crucial for reliable component design across scales. Understanding the deformation mechanisms could also help to inspire new insight in designing novel components with controlled mechanical properties. In this thesis, the plastic deformation in single crystal 6H-SiC was investigated. Nanoindentation tests with a Berkovich indenter were conducted on different crystallographic orientations. The experimental data obtained was used to calibrate a three-dimensional finite element model with an explicit time integration scheme incorporating a suitably modified crystal plasticity theory. The comparison of load-displacement curves as well as surface topography analysis to experiments have shown that the modelling approach can reasonably elucidate the underlying principles of deformation in this Hexagonal Close Packed like material. The predictions from the simulations indicated that the activation of slip system is rather complicated with activation of the pyramidal family being significant, which differentiated from general beliefs that basal slip is the only dominant slip system when considering plastic deformation in this material. Following this, a nanoscratching experiment was conducted along four different crystallographic orientations. Results showed that although there is not much difference in macroscopic response such as cutting forces, the elastic-plastic transitions and microcrack formation are different. The experimental results from the scratching experiment further strengthen the claims that the slip system activation is complicated and all of the slip systems should be taken into account instead of just considering basal slip when considering plastic deformation in this material. Finally, an enhanced numerical model was developed to account for this deformation behaviour. The modelling framework has the predictive capability of determining machining forces, induced damage and residual stress in the machined component. Such an approach may be used in the component fabrication industry to mitigate the detrimental effects of machining during manufacture.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Mechanical Engineering not elsewhere classified ; Silicon carbide ; Crystal plasticity ; Nanoindentation ; Nanoscratching