A novel strategy for architecting low interfacial energy transition phase to enhance thermal stability in a high-entropy alloy

Abstract

Alloys with high strength and thermal stability are attractive for crucial applications in aerospace and power-generation sectors. In this paper, based on the thermodynamics, the microstructure, hardness, and compressive properties of the (FeCoNiCrCu1.71)96Nb4 and (FeCoNiCrCu1.71)90Nb10 (at%) high-entropy alloys (HEAs) upon high-temperature aging were studied. The results indicate that the addition of Nb increases the amounts of the Nb-rich precipitates and concentration of Nb within the matrix, enhancing the hardness and yield strength. With prolonged aging time, the hardness and yield strength of the (FeCoNiCrCu1.71)96Nb4 and (FeCoNiCrCu1.71)90Nb10 HEAs remain almost unchanged, showing high thermal stability. It is discussed from the synergistic of high-density secondary Cu-rich precipitates and the low-energy Nb-rich precipitate/transition precipitate/matrix and Cu-rich precipitate/matrix interfaces. From a thermodynamical point of view, the free energy of the matrix is decreased to be lower than that of the Nb-rich precipitates, changing the diffusion direction of Nb and forming a gradient distribution of Nb. It provides a convenient strategy to architect an fcc metastable transition precipitate linking Nb-rich precipitates and Cu-depleted matrix, reducing interface energy. Moreover, Cu and the coherent interfaces with low interfacial energy effectively retard the coarsening of the Nb-rich precipitates. It may serve as guidance for the future alloy design strategy of high-entropy superalloys with high thermal stability.