Tuning the microstructural and micro‐/nanomechanical properties of silicon nitride–carbon nanotube composites by powder oxidation

Abstract The effects of the oxidation on the micro/nanohardness, density, and microstructure of the silicon nitride–carbon nanotube (Si ₃ N ₄ –CNT) composite were investigated. α‐Si ₃ N ₄ starting powder was oxidized at a temperature of 1000°C for 10 and 20 h and was used to produce composite samples made via hot isostatic pressing (HIP). Density measurements revealed that the 20‐h oxidized α‐Si ₃ N ₄ ‐based composite had higher apparent density than the unoxidized and 10‐h oxidized ones. The micro/nanohardness results proved that this improvement in the density induces changes in the mechanical properties. After the oxidation process and sintering, the microhardness of the composite remained unchanged at 6.525 and 6.49 GPa for the unoxidized and 10‐h oxidized samples, respectively. However, the microhardness was significantly improved, reaching 8.28 GPa for the 20‐h oxidized samples. Similarly, the best nanohardness results were obtained in the 20‐h oxidized samples, significantly surpassing those of the unoxidized and 10‐h oxidized samples. However, some of the scanning electron microscopy images indicate that the CNTs do not disperse or distribute evenly, explaining the large scatter in the nanohardness results. These findings suggest that the 20‐h oxidation process significantly enhanced the micro‐ and nanohardness and density of the Si ₃ N ₄ –CNT composite, potentially improving its overall mechanical performance.