摘要
<p>High-entropy alloys (HEAs) fabricated by additive manufacturing offer exceptional compositional flexibility; however, controlling grain stability while maintaining high-temperature ductility remains a major challenge. Here, we demonstrate that a minor yttrium (Y) addition (<1000 ppm) markedly modifies the microstructural evolution and tensile behavior of an L12-strengthened HEA produced by laser powder bed fusion (L-PBF). Compared with the baseline alloy, the Y-bearing HEA retains fine, elongated grains (similar to 8 mu m) after homogenization and controlled cooling, whereas the baseline alloy undergoes severe grain coarsening (similar to 75 mu m). Complementary analysis of (S)TEM, three-dimensional atom-probe (3D-AP) and thermodynamic simulation reveals that this stabilization originates from nanoscale Y-rich oxides formed during solidification and distributed along grain boundaries. The multicomponent high-entropy matrix promotes the enthalpy-driven rejection of Y from grain interiors toward grain boundaries. This behavior originates from severe lattice distortion and atomic-size mismatch, enabling preferential segregation and stable oxide formation. The solid-solid partitioning behavior of FCC matrix and L12 phase remained unchanged with addition of yttrium. Tensile testing from room temperature to 900 degrees C shows that the Y-bearing HEA exhibits higher strength at room temperature and 650 degrees C and more than twice the elongation at 750-900(degrees)C without strength loss. Nanoscale Y-rich oxides not only serve as thermally stable grain-growth inhibitors but also suppress stress concentration associated with L21 precipitation through grain-boundary pinning and oxygen scavenging. These findings demonstrate that ppm-level Y microalloying provides an effective grain-boundary engineering strategy for additively manufactured HEAs, offering insights into the design of microstructurally stable alloys with improved high-temperature mechanical performance.</p>