Effect of characterization on fatigue crack growth in a SiC-reinforced silicon nitride composite at 1200{degree}C
- Open Univ., Milton Keynes (United Kingdom)
Subcritical crack growth in a high strength, SiC-reinforced Si{sub 3}N{sub 4} under sustained and cyclic loads at high temperature has been investigated to determine the influence of crystallization on crack growth velocity. Crystallization of the grain boundary glass phase did not produce an observable increase in fracture toughness but did produce increased fatigue crack growth resistance at high temperature. TEM study indicated that this improvement resulted from an observed reduction in glass flow and crack tip cavitation due to the significantly reduced glass phase content after crystallization. It is shown that high temperature fatigue crack growth is predominantly loading time dependent with a weak effect of stress cycles. An influence of loading frequency on crack growth rates occurred only at high loading rates in uncrystallized (high glass phase content) specimens where the crack tip stress intensity was reduced due to viscous bonding of the glass phase at the crack surfaces.
- OSTI ID:
- 605854
- Journal Information:
- Acta Materialia, Vol. 46, Issue 4; Other Information: PBD: 13 Feb 1998
- Country of Publication:
- United States
- Language:
- English
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