Low-temperature preparation of in situ toughened Yb α-SiAlON ceramics by spark plasma sintering (SPS) with addition of combustion synthesized seed crystals

By applying SPS technique, new Yb α-SiAlON ceramics in situ toughened by rod-like grains were prepared at a relatively low temperature of 1600 °C, with combustion synthesized seed crystals added. The effects of sintering temperature, heating rate, and the addition of seed crystals on the densification process, phase transformation, microstructure development, and mechanical properties of the samples were discussed in detail. The experimental results showed that Yb α-SiAlON ceramics could be almost fully densified quickly by SPS, and the fast heating rate was helpful to reduce the amount of intermediate phases. Higher sintering temperature and appropriate holding time were beneficial to the promotion of phase transformation and grain growth. It was also demonstrated that the added seed crystals played an important role in enhancing the phase transformation and facilitating the growth of rod-like grains. Being toughened by the rod-like grains via the mechanisms such as grain pull-out and debonding, the fracture toughness of as-sintered Yb α-SiAlON ceramics with additive seed crystals was remarkably improved.