The Ni-base superalloys possess high stability and strength at high temperatures and therefore they are used in the manufacturing of gas turbine components. The superalloy GTD-111 is frequently employed in the first stage blades of high power gas turbines. The appropriate microstructure and strength is gained through the application of directional solidification and precipitation hardening heat treatment. In this research, several directionally-solidified (DS) GTD-111 specimens were first manufacturd by the Bridgman method under vaccum by the withdrawal rate of 6 mm/min. In order to determine phase transformation temperatures, the differential scanning calorimetry was conducted, based on which the heat treatment temperatures were selected under the solidus temperature of 1295°C. Different cycles of the precipitation hardening heat treatments were applied to the DS specimens and effects of homogenization, primary partial solution, secondary partial solution and aging heat treatments on microstructures were investigated. In addition, the effect of secondary partial solution at temperatures of 910°C, 980°C and 1050°C on the room temperature tensile and stress rupture properties of the heat treated specimens was evaluated. The results showed that the GTD-111 alloy has a multi-phase microstructure consisting of g austenitic matrix, g¢ precipitate, g¢-g eutectic and two types of MC and M 23 C 6 carbides. Moreover, homogenization treatment resulted in a uniform distribution of the g¢ precipitates. It was also observed that partial solution after homogenization led to the growth and preferred distribution of the precipitates along the 100 direction. More growth of g¢ precipitates during secondary partial solution led to the splitting of the g¢ precipitates into a group of fine precipitates. The stress rupture test results showed that a proper distribution of the g¢ precipitates and consequently a higher rupture life was obtained in the heat treatment cycle including homogenization, primary partial solution, secondary partial solution at 980°C. Keywords: Precipitation hardening; Directional solidification; GTD-111 superalloy; Partial solution treatment
