Entropy-driven elemental diffusion and microstructural evolution in Co-based composites reinforced with high-entropy carbonitrides

Abstract

Cermets offer a promising route to meet the demands of harsh environments by combining the ductility of metals with the hardness and thermal stability of ceramics. High-entropy carbonitrides (HECNs), owing to their superior mechanical properties and phase stability, are attractive reinforcement phases. However, interfacial instability and sintering challenges often limit their performance. In this work, three HECN phases, 90 wt%Co-10 wt%(TiNbTa)(C,N) named Co-MECN, 90 wt% Co-10 wt%(TiZrNbTa)(C,N) named Co-4HECN, and 90 wt%Co-10 wt%(TiZrNbMoTa)(C,N) named Co-5HECN, with progressively increasing configurational entropy were incorporated into Co-matrix composites via solid-state sintering. The influence of entropy on diffusion behavior and mechanical response was systematically evaluated. Mo exhibited the highest diffusivity in the Co matrix, followed by Ti, Zr, Nb, and Ta, and this diffusion inhomogeneity induced local stress concentrations that weakened interfacial bonding. The Co-MECN composite achieved the best performance, with a transverse rupture strength of 1.75 GPa and a hardness of 326 kgf/mm², while higher entropy levels led to performance degradation due to increased phase stability hindering densification and promoting pore formation. These findings clarify the dual role of entropy in regulating diffusion and consolidation, providing a guidance for the rational design of next-generation high-entropy cermet systems.