Key factors in quality control of a high Cr content cast Ni‐base superalloy K4648

Abstract

Abstract K4648 possesses the highest Cr content in applied cast Ni‐base superalloys and has been applied to manufacture the integral castings of advanced gas turbines in China. However, the large blocky primary α phase in alloy had detrimental effect on the impact ductility, and the alloy severely reacted with the silica‐based ceramic core during the solidification process. The investigation results indicate that the primary α phase precipitated in the late solidification at 1190 °C. The Vickers microhardness value of α phase is 6.3 GPa at the load of 0.2 N. The primary α phase transforms to M 23 C 6 carbides after solid solution treatment at 1180 °C. The cracked α or transformed M 23 C 6 can be observed at the fracture surface and longitudinal section of the impact specimens. Moreover, the severe reaction exists in the metal/ceramic interface. The reaction products consist mainly of the oxides which elements come from both alloy and silica‐based ceramic core. For high Cr content superalloys, the solidified parameters should be controlled properly to inhibit primary α phase precipitation and more stable alumina‐based core is recommended.