NASA Lewis Research Center, Cleveland, OH
Rockwell International, Rocketdyne Division, Canoga Park, CA
The low-and high-cycle fatigue behavior of three different fiber-reinforced superalloy (FRS) composite materials were evaluated. Each composite material contained 40 vol% unidirectionally aligned continuous length tungsten-1.5 wt% ThO2 fibers. The metal matrices were Waspaloy, Type 316L stainless steel, and Incology 907. Fatigue tests were conducted at 871°C in a helium atmosphere under load control with a load ratio (minimum stress/maximum stress) of 0.2. The composites were found to have excellent elevated temperature fatigue strength. The fibers played a major role in controlling the fatigue strength of the composites. Fatigue crack fronts were found to be retarded by the fibers. The cracks tended to branch at the fiber/matrix interface and grew by a sliding mode along the interface. Matrix surface cracks induced by thermal shock damage had little influence on the fatigue strength of the FRS composites.
Paper ID: CTR10595J