Measuring and understanding grain boundary properties of engineering ceramics
<p>This thesis aims to measure the mechanical properties of ceramics on the microscale using microcantilever beams. Focussed Ion Beam milled triangular cross-sectional beams (approximately 3 x 5 x 20µm) were fractured using a nanoindenter to measure the Young’s modulus, fracture strength, and...
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| Format: | Thesis |
| Language: | English |
| Published: |
2013
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| _version_ | 1797061458080563200 |
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| author | Norton, A Andrew Norton |
| author2 | Todd, R |
| author_facet | Todd, R Norton, A Andrew Norton |
| author_sort | Norton, A |
| collection | OXFORD |
| description | <p>This thesis aims to measure the mechanical properties of ceramics on the microscale using microcantilever beams. Focussed Ion Beam milled triangular cross-sectional beams (approximately 3 x 5 x 20µm) were fractured using a nanoindenter to measure the Young’s modulus, fracture strength, and fracture toughness. By developing the technique with a sapphire bicrystal, it was found that the mechanical properties could be successfully ascertained if correction factors were used. Experiments and theoretical work showed that sapphire and polycrystalline alumina beams undergo moisture assisted sub-critical crack growth when tested in air. Whilst corrections for the Young’s modulus have been previously reported, this is the first reported attempt to correct for the notch tip residual stress and the first to consider sub-critical crack growth.</p> <p>Once these factors were characterised using the sapphire bicrystal, the technique was applied to a range of different ceramics, such as polycrystalline α-alumina and silicon nitride. These are the first reported direct measurements the grain boundary toughness of these ceramics using microcantilever beams.</p> <p>The grain boundary toughness was correlated with the macroscopic fracture properties and the characteristics of the ceramic (grain boundary composition, impurities, and fracture mode). Two grades of α-alumina were used and the macro- and micro-scale properties extensively compared. The damage evolution during uniaxial compression of alumina was investigated in depth, and compared to a previous reported microcrack evolution model using the measured grain boundary toughness. Investigation of whether deformation twins formed during loading was undertaken and the phenomenon was shown to not occur.</p> |
| first_indexed | 2024-03-06T20:31:26Z |
| format | Thesis |
| id | oxford-uuid:312cd97f-8680-4c02-b162-c0c7282bd343 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T20:31:26Z |
| publishDate | 2013 |
| record_format | dspace |
| spelling | oxford-uuid:312cd97f-8680-4c02-b162-c0c7282bd3432022-03-26T13:06:16ZMeasuring and understanding grain boundary properties of engineering ceramicsThesishttp://purl.org/coar/resource_type/c_db06uuid:312cd97f-8680-4c02-b162-c0c7282bd343Microscopy and microanalysisPhysical SciencesMaterials SciencesCeramicsEnglishOxford University Research Archive - Valet2013Norton, AAndrew NortonTodd, R<p>This thesis aims to measure the mechanical properties of ceramics on the microscale using microcantilever beams. Focussed Ion Beam milled triangular cross-sectional beams (approximately 3 x 5 x 20µm) were fractured using a nanoindenter to measure the Young’s modulus, fracture strength, and fracture toughness. By developing the technique with a sapphire bicrystal, it was found that the mechanical properties could be successfully ascertained if correction factors were used. Experiments and theoretical work showed that sapphire and polycrystalline alumina beams undergo moisture assisted sub-critical crack growth when tested in air. Whilst corrections for the Young’s modulus have been previously reported, this is the first reported attempt to correct for the notch tip residual stress and the first to consider sub-critical crack growth.</p> <p>Once these factors were characterised using the sapphire bicrystal, the technique was applied to a range of different ceramics, such as polycrystalline α-alumina and silicon nitride. These are the first reported direct measurements the grain boundary toughness of these ceramics using microcantilever beams.</p> <p>The grain boundary toughness was correlated with the macroscopic fracture properties and the characteristics of the ceramic (grain boundary composition, impurities, and fracture mode). Two grades of α-alumina were used and the macro- and micro-scale properties extensively compared. The damage evolution during uniaxial compression of alumina was investigated in depth, and compared to a previous reported microcrack evolution model using the measured grain boundary toughness. Investigation of whether deformation twins formed during loading was undertaken and the phenomenon was shown to not occur.</p> |
| spellingShingle | Microscopy and microanalysis Physical Sciences Materials Sciences Ceramics Norton, A Andrew Norton Measuring and understanding grain boundary properties of engineering ceramics |
| title | Measuring and understanding grain boundary properties of engineering ceramics |
| title_full | Measuring and understanding grain boundary properties of engineering ceramics |
| title_fullStr | Measuring and understanding grain boundary properties of engineering ceramics |
| title_full_unstemmed | Measuring and understanding grain boundary properties of engineering ceramics |
| title_short | Measuring and understanding grain boundary properties of engineering ceramics |
| title_sort | measuring and understanding grain boundary properties of engineering ceramics |
| topic | Microscopy and microanalysis Physical Sciences Materials Sciences Ceramics |
| work_keys_str_mv | AT nortona measuringandunderstandinggrainboundarypropertiesofengineeringceramics AT andrewnorton measuringandunderstandinggrainboundarypropertiesofengineeringceramics |