Influence of the Nb–Al ratio on homogenization behavior and hierarchical microstructures in high-entropy superalloys

Abstract

In this investigation, we explore the impact of the Nb–Al ratio on the microstructural and mechanical properties of high-entropy superalloys (HESAs), focusing on hierarchical microstructures. Utilizing a series of HESAs with varying Nb–Al ratios, our study employs advanced characterization techniques, including differential scanning calorimetry (DSC) for thermal analysis, electron probe micro-analyzer (EPMA) for compositional analysis for the design of a homogenization treatment at 1500 K/24 h. Transmission electron microscopy (TEM) reveals that the increasing Nb–Al ratio refines the γ' precipitates and influences the size and volume fraction of embedded hierarchical γ particles. ThermoCalc equilibrium phase analysis and Vegard's-law calculations reveal a minimal lattice misfit between these phases, highlighting the interplay between Nb–Al ratio and phase stability. The increasing Nb–Al ratio inhibits the formation of hierarchical γ particles. We observe an enhancement in hardness from 433 HV to 492 HV with an increasing Nb–Al ratio. This study provides valuable insights into the role of Nb and the Nb–Al ratio in HESAs with hierarchical microstructures, demonstrating its significant influence on γ particle formation within γ' precipitates and mechanical strength. The findings advance our understanding of alloy design and pave the way for developing advanced HESAs for high-temperature applications.