Perspectives of innovations in superalloys for gas turbines

Abstract

Gas turbines have prominence to utilize nickel base superalloys. There are different generations of nickel base superalloys developments. Of these refractory elements addition has been an important process. These have raised alloy element segregation tendencies to necessitate prolonged homogenization treatment. However directional solidification (DS) followed by mushy zone solution treatments have produced primary dendrites incorporated with secondary dendrites distributions. The bimodal microstructures have rendered to be highly interesting to resist aggressive weather of gas turbines. Crack formation in DS alloys have stated to be along single crystal growth direction necessitated to refurbish for reutilization by more than 2 to 3 times its primary life. The conventional welding has stated to be more complex with increasing refractory element additions. Laser welding have been better performer in this response. Heat affected zone (HAZ) cracking has been predominating failure mode by constitutional and bimodal intergranular liquation tendencies. These have recovered by wettable liquation product formations that bear tendencies of matrix metal penetration. In the strategy of surface protection has been another way to raise life. Sulphidation, halogenation, chlorination and oxidation at high temperature have been main modes to initiate failure. Surfacing with intermetallics or cermets has found to be optimized for prevention of these failures.