ELEVATED-TEMPERATURE FATIGUE BEHAVIOR OF TUNGSTEN FIBER-REINFORCED SUPERALLOY COMPOSITES

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 Incoloy 907. Fatigue tests were conducted at 871 degrees 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 made along the interface. Matrix surface cracks induced by thermal shock damage had little influence on the fatigue strength of the FRS composites.