Effect of Carbon Nanotube Addition on Densification Behavior, Activation Energy, and Microstructural Evolution of WC-Co Cemented Carbides

This study investigates the effect of carbon nanotube (CNT) addition on the densification behavior, activation energy, microstructural evolution, and mechanical performance of WC-Co cemented carbides processed by liquid-phase sintering. WC-Co and WC-Co reinforced with 5 vol.% CNT were fabricated by powder metallurgy and sintered under argon atmosphere at temperatures between 1380 and 1400 °C using different holding times. Relative density measurements, dilatometric analysis, scanning electron microscopy, and Vickers hardness and fracture toughness evaluations were performed to assess the influence of CNT incorporation on the sintering response and resulting microstructure. The results showed that increasing sintering temperature and holding time promoted densification and microstructural consolidation in both systems. Although CNT addition slightly reduced the final relative density, it promoted a finer and more homogeneous carbide distribution. Dilatometric analysis revealed that CNT incorporation modified the densification kinetics and increased the apparent activation energy from 99.36 ± 8 kJ/mol for WC-Co to 126.47 kJ/mol for WC-Co + 5 vol.% CNT, corresponding to an increase of approximately 27%, indicating significant changes in the diffusion-controlled mass transport mechanisms governing liquid-phase sintering. Furthermore, the CNT-reinforced material exhibited improved mechanical performance, reaching hardness and fracture toughness values of approximately 1090 kgf/mm2 and 10.5 MPa·m1/2, respectively, compared with 995 kgf/mm2 and 8.6 MPa·m1/2 for the unreinforced WC-Co system. Enhanced fracture resistance was further supported by reduced crack propagation after Vickers indentation. The results demonstrate that CNT incorporation acts not only as a reinforcing phase but also as a microstructural and kinetic modifier, providing an effective strategy for controlling densification behavior and improving the performance of WC-Co cemented carbides processed by liquid-phase sintering.