Enhancing the Creep Strength of Next-Generation Disk Superalloys via Local Phase Transformation Strengthening

Abstract

A new disk superalloy has been developed by NASA to improve high-temperature creep performance utilizing the recently discovered local phase transformation strengthening mechanism. Creep tests were performed at 760 °C and 552 MPa, to approximately 0.3% plastic strain, a regime where the formation of γ′ shearing modes such as superlattice extrinsic and intrinsic stacking faults are active. The new alloy exhibited superior creep performance over the current state-of-the-art superalloys, ME3 and LSHR. High-resolution characterization confirmed the formation of the strengthening η phase along superlattice extrinsic stacking faults and χ phase along superlattice intrinsic stacking faults. In addition, creep deformation analysis via scanning transmission electron microscopy appears to show a significant reduction in microtwin formation as compared to LSHR and ME3. This improvement in creep performance was also accompanied by an improvement in both room temperature and high-temperature strength.