Corrosion resistance enhancement via σ phase suppression by B microalloying in (CrCoNi)94Al3Ti3 alloy

(CrCoNi) 94 Al 3 Ti 3 medium-entropy alloy (MEA) is mainly strengthened by intragranular L1 2 precipitates, but at aging temperatures that favor L1 2 formation, the Cr-rich σ phase also precipitates at grain boundaries (GBs). The intergranular σ precipitation not only deteriorates the alloy’s ductility but also decreases the corrosion resistance due to the depletion of Cr in the adjacent regions of GBs. In this study, a B microalloying strategy was employed to improve corrosion resistance by suppressing the formation of Cr-rich σ phase at GBs. The effect of B content on precipitation behavior during aging was systematically investigated. The results demonstrate that B addition effectively inhibits Cr migration toward GBs, thereby suppressing Cr-rich σ phase formation. As Cr segregation and σ phase are restrained, Cr-depleted zones along GBs are markedly reduced, and the matrix Cr distribution becomes more homogeneous. This simultaneously enhances intergranular and intragranular corrosion resistance without disturbing the intragranular L1 2 strengthening phase. DFT calculations reveal that B atoms preferentially segregate to GBs. When B occupies GB sites, the segregation energies of Cr become positive, indicating that B addition weakens the dynamic driving force for Cr segregation. Furthermore, B facilitates Cr diffusion toward the surface, promoting the formation of a dense, Cr-rich passive film during corrosion. These theoretical findings align well with experimental observations, providing direct evidence that B-induced modification of Cr segregation behavior is responsible for suppressing σ phase and enhancing corrosion resistance. This microalloying strategy offers a promising approach to improving corrosion performance in Cr rich σ-precipitated alloys.