Finite-Temperature Grain-Boundary Segregation in High-Entropy Carbides

High-entropy carbides are promising candidates for extreme-temperature environments, but their grain-boundary chemistry remains difficult to resolve because segregation involves both chemical disorder and finite-temperature configurational sampling. Here, we quantify temperature-dependent grain-boundary segregation in high-entropy carbides using a universal message-passing atomic cluster expansion (MACE) machine learning interatomic potential combined with a hybrid Monte Carlo–molecular dynamics workflow. A 53.1 (Formula presented.) (Formula presented.) symmetric tilt grain boundary was sampled for six representative high-entropy carbide compositions containing group IV, V, and VI transition metals at 300 and 2000 K. Element-resolved metal-sublattice composition profiles reveal composition-dependent segregation modes. Several chemistries exhibit selective near-boundary enrichment by one or two dominant metals, including Ti/Zr, Mo/Zr, W/Zr, and Cr/Zr motifs, whereas (Formula presented.) shows persistent multi-element co-segregation. Increasing temperature broadens the segregation profiles and expands the chemically perturbed interfacial region, with secondary metal species contributing more strongly to the near-boundary composition at 2000 K. A Cr-containing composition shows the most pronounced high-temperature response, where Cr-rich segregation is accompanied by boundary broadening, chemical heterogeneity, and structural disordering. These results show that grain-boundary segregation in high-entropy carbides does not follow a single universal trend, but instead depends strongly on carbide chemistry and temperature.