Limitations of grain refinement in solute-modified CoCrNi: The role of constitutional supercooling in PBF-LB

Artikel i vetenskaplig tidskrift, 2026

Additive manufacturing of medium-entropy alloys offers unique opportunities for fabricating complex metallic components with enhanced mechanical properties. However, this processing route is often challenged by the formation of columnar grains and microstructural anisotropy. In this study, a solute-based strategy leveraging constitutional supercooling was explored to promote grain refinement in a CoCrNi alloy. Ti was selected through thermodynamic calculations due to its high growth restriction factor ( Q ) and favorable solubility, and a (CoCrNi)97Ti3 (at%) composition was produced via in-situ alloying using powder bed fusion - laser beam. Although grain size refinement was not observed, Ti addition disrupted columnar grain growth and promoted a more equiaxed morphology, likely due to modified melt pool dynamics associated with in-situ alloying. Complementary casting and single-track experiments confirmed that steep thermal gradients inherent to PBF-LB processing can suppress solute-driven grain refinement. Thermal analysis further revealed lower experimental Q values compared to predictions, evidencing limitations in the thermodynamic data employed. Additionally, the high solidification rates during laser processing slightly reduced segregation, contributing to a slightly lower effective Q value. These findings highlight the importance of linking solute selection with process-specific solidification conditions and provide new insights into the combined effects of alloy chemistry, melt pool dynamics, and thermal gradients in medium-entropy alloys processed by additive manufacturing.