The characteristics of γ' precipitates in a superalloy quenched from 1050℃ at different rates were investigated using field emission scanning electron microscope (FESEM). When quenched from 1050℃, the size of primary aging y' precipitates has a small increase in the specimens that experienced iced-brine-quenching, oil-quenching, and air-cooling-quenching conditions and a drastic increase in the specimen that experienced a furnace-cooling-quenching condition. The cooling γ' precipitates have unimodal distributions after quenching at the air-cooling rate and bimodal distributions after quenching at the furnace-cooling rate, but there are not these distributions in the specimens that experienced iced-brine-quenching and oil-quenching conditions. When aging at 760℃, the size of primary aging γ' precipitates appears unaffected in the specimens that experienced iced-brine-quenching, oil-quenching, and air-cooling-quenching conditions. However, it has a drastic increase in the specimen that experienced a furnace-cooling-quenching condition, and it is interesting that the bigger cooling γ' precipitates have a coalescence and octodendritic shape. The microhardness study indicates that the hardness has no variation in the specimens that experienced iced-brine-quenching, oil-quenching, and air-cooling-quenching conditions and has a drastic decrease in the specimens that experienced a furnace-cooling-quenching condition and obtains the minimum microhardness value 390.8 HV.
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