Microstructure and Hot Tearing Susceptibility of K418 and K419 Superalloy for Auto Turbocharger Turbine Wheel

摘要

K419 superalloy turbine wheel was more susceptible to hot tearing than K418 one when they were used for auto turbocharger turbine wheel. The fracture and microstructure characteristics in the K418 and K419 turbine wheel blades were analyzed. The segregation of alloying elements was analyzed by EDS. The probable equilibrium phases in the two kinds of superalloys, the effects of aluminum, titanium and niobium contents on the precipitation of γ' and γ/γ' eutectic phase and the segregation of alloying elements were studied by Thermo-Calc software. The results show that the hot tearing in the K418 and K419 superalloy turbine wheel blades is caused by the fracture of dendrites structures, while the amount of γ/γ' eutectic in K419 is more than that in K418, resulting in K419 being more susceptible to hot tearing. Titanium and niobium, the strong positive segregation elements promote the formation of γ/γ' eutectic, which lead to severe hot tearing susceptibility of the superalloy.