Aging an Fe-Ni-Co-Nb-Ti-Si superalloy under tensile stress

The precipitation behavior during aging at temperatures between 720 degrees C to 950 degrees C, both with and without a tensile stress, was investigat ed in a controlled low thermal expansion Fe-Ni-Co-Nb-Ti-Si superalloy, Inco loy alloy 909. Higher density and larger epsilon plates formed in the sampl es aged with a tensile stress. Furthermore, the tensile stress enhanced the growth of grains during aging at temperatures higher than 850 degrees C. I n the specimen aged at 950 degrees C with a tensile stress, one set of a pl ates were found to orient nearly along the tensile load axis. "Black grains " were still found in the aged microstructure even if the material was full y recrystallized.