Microstructure evolution of directionally solidified DZ125 superalloy with melt superheating treatment

In this paper, the melt superheating treatment is carried out for DZ125 superalloy during directional solidification. With appropriate superheating treatment regulation, the thermal gradient and solidification velocity remain constant for different melt superheating temperatures in order to accurately investigate the relationship between the solidification microstructure and the melt superheating treatment. The results show that dendrite arm spacing and dendrite segregation have change obviously with the melt superheating temperature increasing from 1500 °C to 1750 °C although the thermal gradient and withdraw velocity are unchanged. The carbide morphology presents from script-like to blocky and nodular with the increase of melt superheating temperature. The variations of dendrite arm spacing and alloy element segregation rations are arose from the change of freezing range and solute distribution coefficient. The variations of MC carbide's morphology and size are related to the disappearance of MC carbide clusters in melt and the change of freezing range with the increase of melt superheating temperature. But the intrinsic reason is the variation of melt structure after melt superheating treatment. The melt superheating treatment is carried out for DZ125 superalloy during directional solidification. Under the same thermal gradient and solidification velocity, the microstructure evolution of directionally solidified DZ125 superalloy is systematically investigated by changing the melt superheating temperature. The results show that the dendrite is refined with the melt superheating temperature increasing from 1500 °C to 1650 °C. However, it becomes coarse after the melt superheating treatment at 1750 °C. The dendrite segregation first reduces with the increase of melt superheating temperature between 1500 °C and 1650 °C, but becomes more severe when the superheating temperature is higher than 1650 °C. The carbide morphology presents script-like when the melt superheating temperature is below 1600 °C. Further increasing the melt superheating temperature, it is mainly blocky and nodular. Moreover, the reason of microstructure evolution with melt superheating treatment is discussed. The results are useful for promoting the development of high quality directionally solidified superalloy.