On the precipitation hardening of the directionally solidified GTD-111 Ni-base superalloy: Microstructures and mechanical properties

Effects of precipitation hardening on microstructures and mechanical properties of the directionally-solidified (DS) Ni-base GTD-111 superalloy are investigated. DS specimens were subjected to different cycles of solution treatments at temperatures of 910 °C, 980 °C and 1050 °C. The solidified and heat-treated microstructures along with the stress rupture properties were evaluated to investigate influence of the homogenization and second solution treatments. The results showed the homogenization treatment resulted in a more uniform distribution of the γ′ precipitates. It was shown that growth and preferred distribution of the γ′ precipitates occurred along the <100> direction in the primary solution treatment. More growth of γ′ precipitates during secondary solution treatment led to the splitting of the precipitates into a group of fine precipitates. The best stress rupture result was achieved in the specimen with the second solution treatment at 980 °C for 2 h followed by aging at 843 °C for 24 h due to the suitable size, volume fraction, and size distribution of the γ′ precipitates in the DS microstructure.