Improvement of the Strength of Silicon Nitride by Aging
The response of silicon nitride to an aging treatment of 165 h at 800°C is studied with the help of four different material conditions: as received, aged, indentation pre-cracked + aged and pre-cracked + flexure-loaded + aged.
The aging treatment results in surface confined material changes that lead to high fracture toughness values and R-curve behaviour. The bulk-fracture toughness and strength are reduced. Pre-cracks heal by the formation of oxides that fill the cracks. Complete strength recovery is obtained for samll pre-cracks. Flexure-loaded pre-cracks expirience pronounced healing. In combination with possible crack closure effects this leads to an enhanced room-temperature strength of such specimens compared to the as received condition.
KeywordsFracture Toughness Silicon Nitride Aging Treatment Indentation Load Crack Healing
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