Microstructure evolution of Ni-base single crystal superalloy under different melt holding time

Using optical microscope and scanning electron microscope, the effect of melt holding time on the microstructure of Nickel-base single crystal superalloy is investigated under the thermal gradient and withdrawal rate unchanged.compared with the sample without melt treatment, the dendrite segregations of W, Mo and Ti are decreased, the dendrite structure and γ′ phase in interdendritic area are obviously refined, meanwhile, the morphology of the γ′ phase becomes uniform when the melt is overheated at 2053 K for 30 min and then hold at 1773 K for 15 min-30 min.