B2-precipitation induced optimization of grain boundary character distribution in an Al0.3CoCrFeNi high-entropy alloy

Abstract

The grain boundary character distribution (GBCD) of Al0.3CoCrFeNi high entropy alloy (HEA) subjected to 5% cold rolling and subsequent annealing at 1000 °C from 1 h to 100 h was investigated. The results show that the microstructure of Al0.3CoCrFeNi HEA is composed of FCC structure and ordered BCC (B2) structure. With the increase of annealing time, the frequency of low coincident site lattice (low-ΣCSL (3 ≤ Σ ≤ 29)) is divided into three stages, i.e., increases slowly in stage I (1–10 h), increases sharply in stage II (10–50 h), and remains stable in stage III (>50 h). The HEA annealed for 100 h possesses the highest low-ΣCSL fraction of ~71.34% and the biggest special boundary cluster, indicating that GBCD is effectively optimized. To this end, GBCD optimization mechanisms are proposed to explain this evolution: strain-induced boundary migration (SIBM) mechanism in stage I, non-coherent Σ3 boundary migration reaction model in stage II, and maintain stability in stage III. In this process, B2-precipitation has a key influence on the evolution of mechanism. B2-precipitation pinning induces the SIBM mechanism in stage I to generate numerous non-coherent Σ3 boundaries, which provides a basis for the non-coherent Σ3 boundary migration reaction in stage II. Therefore, the introduction of precipitation in HEAs provides a new and effective pathway to optimize GBCD.