Low-density CoAlTi-B2 strengthened Al-Co-Cr-Mo-Ti bcc refractory high-entropy superalloy designed with the assistance of high-throughput CALPHAD method

Abstract

Superalloys are being widely used across the globe, in the power plants and turbine engines, due to the superior mechanical performance at elevated temperatures and oxidation resistance in crucial environments. To enhance the currently commercial Ni-based superalloys, refractory elements are desired candidates for novel alloy development, due to their ultrahigh melting points. In the past decade, refractory high-entropy superalloys (RSAs), which are the multi-principal refractory element-based alloys with the microstructure of ordered body-centered cubic (bcc) (B2) precipitates coherently embedded in the disordered bcc (A2) matrix, have attracted great attentions. However, most reported RSAs possess the reversed microstructure of the continuous B2 phase with the discrete A2 phase forming via the spinodal decomposition, which have poor thermal stability at elevated temperatures. Herein we designed a coherent precipitate-strengthened Al-Co-Cr-Mo-Ti RSA with the assistance of high-throughput CALPHAD (HT-CALPHAD) calculations. Pandat software with PanHEA 2021 database were used in searching desired compositions. The alloy was fabricated by vacuum arc melting (VAM) and characterized with X-ray fluorescence spectroscopy (XRF), differential thermal analysis (DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The desired microstructure of CoAlTi-B2 homogeneously dispersed in the A2 matrix was obtained, resulting in the high hardness. The coherent bcc/B2 RSA with high hardness-to-density ratio is being developed.