Fracture chemistry of δ-Al2O3 (Saffil) fibres in an MgLi matrix environment
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Fracture surfaces of δ-Al2O3 (Saffil) fibres embedded in an Mg-8 wt% Li matrix by the pressure infiltration process were investigated by in situ Auger electron spectroscopy to study the chemistry of embrittlement of the former, resulting from a cross-section attack by the molten Mg-8 wt% Li matrix. The unaffected fibres failed transgranularly without any indications of silica being the crack-controlling flaws. Displacement reductive reactions between fibre constituents (δ-Al2O3, silica) and penetrating lithium and magnesium species produce the phases that disturb the structural coherency of fibres and provide the paths for the crack propagation. In the early fibre/matrix reaction stage (slightly affected fibres) there are elemental silicon and aluminium and, most likely, also Li2O that cause the intergranular fracture of fibres, whereas in the advanced reaction stage (strongly affected fibres), MgO is predominantly formed and the fracture propagates throughout the fibres via the MgO-enriched regions.
KeywordsAuger Electron Spectroscopy Fracture Path Auger Spectrum Enrich Region Elemental Silicon
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