Effect of Composition on Grain‐Boundary Chemistry and Fracture Behavior in High‐Entropy Carbides

ABSTRACT High‐entropy carbides (HECs) are often treated as a single material class defined by configurational entropy; however, their properties are governed by composition‐specific defects and grain‐boundary chemistry. This study demonstrates that substituting a single element can qualitatively change grain‐boundary structure and fracture behavior in HEC ceramics. Two HECs, (Cr,Hf,Ta,Ti,Zr)C (HEC‐Cr) and (Hf,Ta,Ti,W,Zr)C (HEC‐W), were examined via electron microscopy, atom probe tomography, and molecular dynamics simulations. Simulations predict preferential segregation of Cr, W, and Zr to grain boundaries. Experiments confirmed Cr enrichment at grain boundaries and the formation of W‐rich nanograins along boundary networks. Mechanical testing revealed that these compositional differences translated into grain‐boundary cohesion differences: HEC‐Cr exhibited intergranular fracture and lower compressive strength (2.66 GPa), whereas HEC‐W exhibited transgranular fracture and higher strength (5.95 GPa). These findings establish grain‐boundary segregation as a dominant mechanism linking composition to mechanical performance in HECs and underscore the advantages of integrated chemistry‐microstructure design strategies rather than thermodynamics alone.