Effect of secondary orientation on the microstructures in thin-walled castings of nickel-based single-crystal superalloys

With the increasing turbine inlet temperature of aero-engine, the requirement of temperature capacity of turbine blades is more stringent. A variety of complex cooling structures have been designed, among which the micro cooling represented by lamilloy is the latest development. At present, the thickness of lamilloy turbine blade is 0.5 mm or less. The reason for performance degradation caused by thin-walled is still controversial and the understanding of dendrite growth behaviour under space constraints is insufficient. In this study, 0.75 mm wall thickness nickel-based superalloy DD403 samples were cast by high-rate directional solidification. The growth and evolution of dendrites in plank-shaped specimens with different secondary deviation angles were investigated. The variation of dendrite spacing and the arrangement of dendrites under different secondary deviation angles were studied. It is found that the primary dendrite arm spacing in the thin-walled region decreased with the increase of the secondary deviation angle, but there was no significant change in the average size of 3′ phases and elements segregation.