Effect of Iron Oxide on Sintering Behavior of Silicon Nitride Ceramics

Silicon nitride ceramics were prepared using alumina and magnesium fluoride as sintering aids and zirconia as the reinforcing phase. Additionally, iron oxide was introduced, with varying content. The relationship between the content of iron oxide and density, mechanical properties, and phase composition of the silicon nitride ceramics was studied. Furthermore, the migration and transformation of iron oxide within the silicon nitride matrix during the sintering process was examined. During the sintering process, partial dissolution of aluminum oxide and iron oxide into the silicon nitride lattice was observed. Interestingly, the introduction of iron oxide exerted a noteworthy influence on the phase transition of silicon nitride. This influence ultimately manifested as a reduction in hardness, coupled with an enhancement in strength and fracture toughness of the samples. The sample without iron oxide had the highest relative density and hardness, with relative density, flexural strength, hardness, and fracture toughness of (93.47±0.28)%, (359.73±2.86) MPa, (13.40±0.48) GPa and (2.39±0.074) MPa·m^1/2, respectively. The sample with 1% iron oxide had the highest bending strength and fracture toughness, with relative density, bending strength, hardness, and fracture toughness of (92.17±0.17)%, (405.30±8.53) MPa, (11.36±0.56) GPa and (2.96±0.053) MPa·m^1/2, respectively.