The role of Mg2Si additive in sintering silicon carbide

Highlights: • A novel Mg₂Si sintering additive was proposed to sinter SiC for the first time. • A high relative density of 96.86% was obtained. • The microstructure of Mg₂Si and interface structure of SiC/Mg₂Si were clarified. A novel Mg₂Si sintering additive was introduced to improve the relative density of SiC ceramic. The SiC samples were hot press sintered at 0.5, 2 and 4 h. The microstructure and relative density were measured, the distribution, microstructure and orientation of Mg₂Si were characterized, and the interface of SiC/Mg₂Si was observed. Results show that relative density of the ceramics increased with the prolongation of sintering time, and densification fulfilled when sintered at 2 h, resulting in the high relative density of 96.86%. With the prolongation of sintering time, the pores become coarsening and the densification process was protracted. Some Mg₂Si react with SiC matrix, and the Mg element distributes into the SiC matrix. The fraction of deformed grains and the geometrically necessary dislocations decreased initially then increased slightly with the prolongation of sintering time. The fraction of low angle boundaries is small in all the samples and the transition from low angle boundaries to high angle boundaries is not smooth. The Mg₂Si grains locate on the grain boundaries of SiC with little misorientation, resulting in a perfect lattice coherence between SiC and Mg₂Si.