Competing densification and interfacial destabilization in HPHT-consolidated CoCrFeMnNi–Ti₃SiC₂–SiC hybrid composites

High-pressure high-temperature (HPHT) consolidation creates a distinct thermodynamic regime for processing high-entropy alloy (HEA)-based composites, where rapid densification may coexist with intensified interfacial reactions and phase instability. In this study, CoCrFeMnNi composites reinforced with 10 wt.% Ti₃SiC₂ and 5 wt.% SiC were consolidated at 6 GPa in the temperature range of 1000–1400 °C to investigate the coupled evolution of densification, phase constitution, microstructure, and hardness. Increasing the consolidation temperature from 1000 °C to 1100–1300 °C significantly improved densification, increasing the relative density from ~82% to nearly 98%, while the hardness increased from 418 HV1 to a maximum of 681 HV1. XRD, SEM, TEM, and STEM-EDS analyses revealed that this behavior was associated with improved interfacial bonding together with progressive activation of diffusion-assisted interfacial reactions involving partial Ti₃SiC₂ destabilization and redistribution of Ti, Si, Cr, and C. At 1300 °C, nanoscale Cr- and C-rich precipitates contributed to additional strengthening, whereas further increasing the temperature to 1400 °C promoted chemical heterogeneity, pore formation, and microstructural degradation, leading to reduced density and hardness. The results demonstrate that HPHT consolidation of Cantor alloy–Ti₃SiC₂–SiC composites is governed by a competition between pressure-assisted densification and temperature-activated interfacial destabilization, resulting in a narrow processing window for achieving optimal microstructural stability and mechanical performance.