Abstract

Fatigue behavior of woven melt infiltrated (MI) SiC/SiC ceramic matrix composites (CMCs) was investigated under a fatigue condition in a combustion environment. A special experimental facility is designed to subject the CMCs under simultaneous mechanical and combustion conditions which is more representative of some conditions experienced by the hot section components of a jet engine. The MI SiC/SiC material considered in this study consists of a SiC matrix, BN interphase and reinforced with two different fibers namely Hi-Nicalon type S and Tyranno SA fibers. A high velocity oxygen fuel (HVOF) gun is used to create the representative combustion condition and a horizontal hydraulic MTS machine to apply the mechanical loading. Several fatigue tests were conducted at different stress levels with a stress ratio of 0.1, frequency of 1 Hz and the specimen surface temperature at 1200 °C. Similar tests were conducted in an isothermal furnace at 1200 °C for comparison. Electrical resistance (ER) was used to monitor the tests. A reduction in fatigue life was observed for the two MI systems under combustion conditions in comparison to the isothermal furnace condition which is attributed to the presence of harsh combustion environment present in the burner rig. Specimens that achieved the runout condition were subsequently tested under monotonic tension testing at room temperature to evaluate the residual properties. Residual strength results showed significant strength reduction in both the furnace and burner rig environments. Post-test microscopy was conducted on the fracture surfaces.

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