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The Ni-base superalloys possess high stability and strength at high temperatures and for this reason they are used in manufacturing of gas turbine hot components. GTD-111 is one of them employed in manufacturing of the first stage blades of high power gas turbines. The alloy gains its appropriate microstructure and high temperature strength through precipitation hardening mechanism. Heat treatment parameters such as: time and temperature of homogenization, partial solution and aging temperatures, and cooling rate from homogenization and solution temperatures affect the microstructure of this alloy. In this paper, the effects of some heat treatment parameters on microstructure were investigated. It was cleared that with long time homogenization at 1200°C local melting of γ–γ′ eutectic occurs and in conclusion, the volume percent of the eutectics decreases. Also, it was shown that size, shape and volume …