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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: A systematic study of the effects of alumina, yttria and zirconia sintering additives on the microstructure and high temperature creep properties of silicon nitride

Author: BLUGAN, Gurdial

Year: 2002

Supervisor(s): Mike Reece

The effects of the sintering additives alumina, yttria and zirconia on the microstructure and properties of silicon nitride have been investigated. The effect of a large range of compositions was investigated using the novel technique of a diffusion couple.

Diffusion couples containing alumina and yttria sintering additives, were produced with and without zirconia doping. The microstructures of these diffusion couples were characterised using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Using the results of the microstructural characterisation, material compositions with potentially good creep properties were identified. Bulk specimens of silicon nitride where then produced for microstructural and mechanical evaluation. The criteria was to produce bulk silicon nitride materials with high densities, refractory second phases and minimal glass content so as to produce materials with good high temperature creep resistance. The microstructural characterisation of the bulk specimens was performed using the same techniques as for the diffusion couples. The mechanical evaluation consisted of room temperature indentation, and high temperature flexural creep testing (between 1200 and 1350oC).