Microstructure evolution and creep property of an equiaxial-single crystal dual-alloy & dual-performance superalloy at intermediate temperature

Dual-alloy & dual-performance superalloy is a key material for blisks, which are widely used in small gas turbines and missile engines. Conventional blisks consist of columnar crystal blades and equiaxed crystal disk. However, the resulting mechanical properties is insufficient to meet the increasing performance requirements of aeroengines. To address this limitation, single crystal superalloys with excellent mechanical properties were considered to introduce. In this study, an equiaxed-single crystal dual-alloy & dual-performance superalloy consist of K447A and DD412 alloys was successfully cast for the first time. The microstructural characterization shows that the dual-alloy bar exhibits good metallurgical bonding, which consists of a DD447A region (K447A alloy with single crystal structure) and a compositional transition zone (CTZ). The contents of carbides and eutectic decrease gradually across this transition zone, whereas the γ′ volume fraction varies shows the opposite trend. On the basis of the good metallurgical bonding, the dual-alloy bar exhibits an excellent creep performance, which is consistent with that of K447A alloy. Further analysis indicates that the creep fracture is primarily initiated by pre-existing cracks in carbides, which will propagate along the interdendritic regions during the creep and ultimately cause failure. TEM observations reveal that the dislocations shear into the relatively non-deformable carbides, leading to internal cracking. Creep deformation is mainly associated with dislocations moving in γ channels, as well as the partial dislocations shearing into γ′ phase, which results in stacking fault formation. This study lays a foundation for developing blisks based on dual-alloy & dual-performance superalloy.