Entropy-driven densification of medium-entropy alloys with laser powder bed fusion

Anomalies inherent to laser-based additive manufacturing (AM), including porosity and structural defects, present significant barriers to fabricating high-integrity metallic structural components. These unavoidable anomalies can significantly degrade the long-term properties of metals, including fatigue, creep, and corrosion, thereby limiting their use in critical environments. In this study, we overcome this challenge with a single-step entropy engineering strategy. By integrating CoCrNi and 316 L powders and enabling temporal changes in entropy evolution during printing, we obtained a nearly void-free (density > 99.99%) medium-entropy alloy with exceptional fatigue resistance and corrosion performance, surpassing conventional PBF-LB/Med medium- and high-entropy alloys. By combining macro-scale densification analysis, micro-scale SEM/EBSD observations, and nano-scale TEM investigations, our results revealed that the increase in configurational entropy during the AM process, together with changes in microstructure, can modify the thermal history, thereby optimizing melt pool spreading. This modification promoted the formation of a uniformly distributed, subgrain-predominated microstructure with a relatively low geometrically necessary dislocation density, which is relatively stable under external loading. This work presents a single-step approach to overcoming the long-term property limitations of AM-fabricated components. In-situ entropy modulation during the laser powder bed fusion process is used to fabricate a near-defect-free alloy (relative density >99.99%) which exhibits exceptional fatigue crack growth resistance and corrosion performance.