The effects of ytterbium oxide on the microstructure and R-curve behaviors of silicon nitride

Silicon nitride materials containing various compositions of Yb2O3 were investigated. The effects of sintering additives on the microstructure, fracture and R-curve behaviors were studied. The average grain size and aspect ratio increased with the amount of Yb2O3 additives. The growth of β-grains started growing from pre-existing β-grains (seeding) until impeded by other β-grains. Growth of crystalline phase with planar font was observed inside amorphous pockets. Heterogeneous growth of secondary crystalline phases from two different ends of amorphous pockets was also noticed. The difference in Yb:Si ratio between the amorphous pocket and secondary crystalline phase could inhibit the completion of crystallization. R-curve behaviors were observed in Yb2O3-doped silicon nitride.