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

The precipitation behavior during aging at temperatures between 720°C to 950°C, both with and without a tensile stress, was investigated in a controlled low thermal expansion Fe-Ni-Co-Nb-Ti-Si superalloy, Incoloy alloy 909. Higher density and larger ε plates formed in the samples aged with a tensile stress. Furthermore, the tensile stress enhanced the growth of grains during aging at temperatures higher than 850°C. In the specimen aged at 950°C with a tensile stress, one set of ε plates were found to orient nearly along the tensile load axis. 'Black grains' were still found in the aged microstructure even if the material was fully recrystallized.