Effect of Phase Decomposition and Elemental Partitioning on Pitting Corrosion Susceptibility in Additively Manufactured High-Entropy Alloys

Additive manufacturing generally endows high-entropy alloys (HEAs) with distinctive microstructures and excellent properties unattainable by conventional processing. This study elucidates how annealing-induced phase decomposition and elemental partitioning govern pitting corrosion behavior in a laser-directed energy-deposited (LDED) Al0.5CoCrFeNi HEA. Notably, the rapid LDED solidification process produces a metastable B2 phase with anomalously high Cr content in this HEA compared to its conventional manufacturing counterpart. Upon annealing at 650 °C for 1 h, (Cr, Fe, Co)-enriched σ and (Cr, Fe)-enriched body-centered cubic (BCC) phases preferentially precipitate within the B2 phase, concurrently depleting Cr and enriching Al in the residual B2 matrix. This elemental repartitioning critically degrades the protective capability of the B2 phase’s passive film, thereby compromising the alloy’s overall pitting corrosion resistance, as evidenced by decreased pitting and repassivation potentials. These findings advance the fundamental understanding of corrosion mechanisms in additively manufactured HEAs and offer a mechanistic rationale for designing corrosion-resistant HEAs via controlled phase transformation.