Effect of Sintering Temperature on Microstructure and Properties of Gas Pressure Sintered Ferrosilicon Nitride

Ferrosilicon nitride ceramics were fabricated via gas pressure sintering (GPS) using micron sized ferrosilicon nitride as a raw material and Al₂O₃-Y₂O₃ as sintering aids. The phase composition and microstructure of the specimens were analyzed by X-ray diffraction and scanning electronic microscopy, and the effect of sintering temperature on the microstructure and mechanical properties of ferrosilicon nitride ceramics was investigated. The results show that β-phase ferrosilicon nitride ceramic with a high density and good mechanical properties can be obtained by GPS. The density, flexural strength and fracture toughness of the samples firstly increase and then decrease with increasing the sintering temperature. The highest density, flexural strength and fracture toughness of the samples sintered at 1 770℃ are 3.31g/cm³, 435 MPa and 6.97 MPa·m^1/2, respectively. Below 1 770℃, the main crystal phase is elongated columnar β-Si₃N₄, which is uniform and well-developed. The compact connection between the grains results in the less pores of grain boundaries. The reactions of iron containing phase and silicon nitride occur as sintering temperature further increases, leading to the increase of porosity and the decrease of flexural strength and fracture toughness. The non-nitrided iron-rich particles exist in the sintered bodies, which could be removed for the further increase of the mechanical properties of Fe-Si₃N₄ ceramic.