Effect of heating rate on spark plasma sintering of a nanosized β-Si₃N₄-Based Powder

A nanosized β-Si₃N₄-based powder doped with sintering additives of 6 wt% Al₂O₃ and 8 wt% Y ₂O₃ were sintered by spark plasma sintering at different heating rates. The in situ shrinkage curves were measured to identify the densification mechanism during the rise in temperature. At slower heating rates (50 and 100°C/min), the nanosized grains are maintained after sintering at 1600°C for 5 min, while anisotropic grain growth is accelerated above 1500°C by applying a rapid heating cycle (200°C/min). In addition to the dynamic Ostwald ripening that occur during the sintering process, the presence of Morié fringes and dislocations is attributed to grain rotation and misfit strain between the subgrains and elongated, large grains. Grain coalescence is found to occur in the rapid heating process.