The Effect of Nano-B4C Additive on Microstructure and Mechanical Properties of Pressureless Sintering SiC Bodies

In this study, the mechanical properties, microstructure, and fracture behavior of SiC-NanoB4C composites have been investigated with different weight percentages of secondary phase including 0, 0.25, 0.5, 0.75, 1, 2, and 3 wt.% nanoB4C produced by pressureless sintering. At least 1 wt.% of phenolic resin was added to all samples as a carbon source (both as a binder and as a carbon additive). Samples were then sintered for 2h at 2150˚C under an argon atmosphere. The results showed that the composite containing SiC-0.5wt% nanoB4C, sintered at 2150˚C, had the best mechanical properties. In this sample, the relative density was 98.32%, the micro-hardness was 28.6 GPa, Young's modulus was 471.8 GPa and the fracture toughness was 3.7 MPa.√m. Also, the transgranular fracture was observed in the related SEM images. Larger amounts of additives reduced the properties. In order to compare the results better, the temperature and duration of the sintering, the micron-scale size of the B4C additive, the amount of phenolic resin, and the amount of initial sample press were considered as variables.