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The fabrication and microstructural evolution, at elevated temperatures, of syalon ceramics
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Winder, Stephen Morley (1985) The fabrication and microstructural evolution, at elevated temperatures, of syalon ceramics. PhD thesis, University of Warwick.
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WRAP_Theses_Winder_1985.pdf - Submitted Version - Requires a PDF viewer. Download (9Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b1445861~S15
Abstract
A number of experimental grade Syalon Ceramics, pressureless sintered materials prepared from the system Y-Si-Al-O-N, were prepared at Lucas-Cookson Syalon Ltd. (Birmingham). Different series of ceramics were composed with of α-Si3N4 powder provided by different manufacturers, and each series contained alloys of varying (effective) AIN content.
Microstructural characterisation of selected alloys was completed using the techniques of optical microscopy, x-ray diffractometry, electron microscopy with x-ray microanalysis, and energy loss spectroscopy. For 'as-sintered' ceramics, the results Indicate a trend in microstructural parameters with (effective) AIN content, such that the mean Al2O3 substitution level in the βSi6-zAlzOzN8-z (major) phase, and the N/O ratio of the inter-β (minor) glassy phase, both increase with Increased AIN addition. A linear relationship between increasing (Y + 0) content in the 'as mixed' alloy composition and increasing glass volume fraction in the microstructure, formed under given sintering conditions, was demonstrated.
Passive oxidation occurred during heat-treatment in air, in the temperature range 1100-1500°C, and formation of β-Y2Si2O7, crystals on the scale surface was noted.
Two crystalline phases, Y3Al5O12 (YAG) and α, (yttrium disilicate), were produced during devitrification of the intergranular phase, in the temperature interval 1100-1500°C. The volume ratio Y3Al5012 : Y2Si2O7, in the heat-treated microstructures, was found to increase as heat-treatment temperature and glass nitrogen content Increased.
Creep tests were performed in the temperature range 1100-1300°C and enhanced creep resistance was demonstrated for materials of lower intergranular phase content, in which nitrogen levels are higher. Morphological changes occurring in the sub-surface and bulk of the ceramics, due to oxidation and crystallisation reactions, were found to cause a time dependent transient in creep behaviour.
| Item Type: | Thesis or Dissertation (PhD) | ||||
|---|---|---|---|---|---|
| Subjects: | Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General) |
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| Library of Congress Subject Headings (LCSH): | Ceramic materials., Ceramics -- Research, Ceramic materials -- Heat treatment | ||||
| Official Date: | September 1985 | ||||
| Dates: |
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| Institution: | University of Warwick | ||||
| Theses Department: | Department of Physics | ||||
| Thesis Type: | PhD | ||||
| Publication Status: | Unpublished | ||||
| Supervisor(s)/Advisor: | Lewis, M. H. (Mike H.) | ||||
| Sponsors: | Lucas Cookson Syalon Limited | ||||
| Format of File: | |||||
| Extent: | vi, 145, [9] leaves : illustrations, charts | ||||
| Language: | eng |
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