Creep Properties and Solute Atomic Segregation of High-W and High-Ta Type Powder Metallurgy Superalloy

Developing superalloys and improving their temperature capability are extremely crucial for the advancement of aero-engines. The powder metallurgy (PM) technology can prevent the macroscopic segregation caused by casting and create a high-alloying aero-engine turbine disk alloy having remarkable microstructural homogeneity and superior thermal capability. PM superalloys have been developed into the 3rd generation alloys for decades, and alloys such as Rene104 already entered service. The chemical composition of the 4th generation PM superalloy is still being researched with the aim of increasing the temperature capability for disk applications to 815 degrees C. In this work, the remarkable creep resistance and creep strengthening mechanism of a novel high-W and high-Ta type PM superalloy GNPM01 was examined. The creep deformation mechanism of GNPM01 alloy and the segregation of elements on deformation defects were investigated using advanced spherical aberration-corrected scanning transmission electron microscopy. The results reveal that the creep resistance of GNPM01 alloy is considerably higher than that of the 3rd generation PM superalloy. The temperature capacity of GNPM01 alloy is approximately 40 degrees C greater than that of FGH4098 alloy under the creep condition of 600 MPa and 1000 h. The creep strength of GNPM01 alloy is approximately 160 MPa higher than that of the FGH4098 alloy at 815 degrees C. In the experimental conditions, the creep deformation behavior was dominated by deformed microtwins, and the GNPM01 alloy clearly slowed down the widening of extended stacking faults and the thickening of microtwins during the creep deformation. It was discovered that the element enrichment of Co, Cr, and Mo existed in the microtwins, and the phase transformation of the twin-structure in gamma' phase was disordered because of the segregation of Co, Cr, and Mo by atomic-level energy dispersive Xray spectroscopy. The isolated superlattice stacking faults in FGH4098 alloy also occurred in the disordered phase transitions. The disordering of superlattice stacking fault or microtwin structure was due to the segregation of Cr, Co, and Mo, which also resulted in the a/6<112> Shockley partials shearing.' phase without producing high-energy nearest-neighbor Al-Al bonds. The segregation disordered the L-2(1) structure resulted in reduced pinning of partials by the ordered gamma' phase, which increased the creep rate of the alloy. During the GNPM01 alloy creeping at 815 degrees C, solute atoms W, Ta, and Nb segregated at the isolated superlattice extrinsic stacking fault (SESF) had ordered atomic occupancy. The fault-level local phase transformation occurred in isolated SESF, forming the [(Ni, Co)(3)(Ti, Nb, Ta, W)] ordered. phase that can effectively inhibit the formation and expansion of microtwins, thus lowering the creep rate of GNPM01 alloy.