Design and thermomechanical properties of a γʹ precipitate-strengthened Ni-based superalloy with high entropy γ matrix

Abstract

A novel Ni-based superalloy was designed with γʹ precipitate strengthening, controlled γ/γʹ lattice misfit and high configurational entropy of the γ matrix for improved high temperature performance up to 800 °C. The alloy contains nano-sized γʹ precipitates, MC and other grain boundary carbides. Three variants of the alloy were fabricated using vacuum induction melting, a computational-based homogenization cycle for reducing solidification segregation, and thermomechanical processing steps of forging followed by hot rolling to produce plates from which ASTM standard test specimens were extracted. Tensile testing at room temperature and elevated temperatures up to 800 °C revealed superior yield stress when compared to Nimonic 105 with good tensile strength values. Furthermore, the three alloys are machinable with maximum stresses comparable to standard practices as determined using deformation mechanisms maps obtained from Gleeble testing and EBSD analysis. Due to the composition of the experimental alloys falling outside the typical range used to populate thermodynamic databases, differences in phase predictions and related temperatures were observed between the experiment and Thermo-Calc predictions. The γʹ forming elements Ti and Nb had a similar effect on the γʹ precipitates and indirectly contributed to changing the entropy of the γ matrix. Based on the results of this study, these alloys have the potential for use at 800 °C in energy structural applications. Definitions related to this novel class of alloys are discussed.