Effects of MgO-RE2O3 and SiO2-RE2O3 (RE = La, Nd, Gd, Ho and Lu) complex sintering additives on the phase composition, microstructure and mechanical properties of dual-phase Si3N4 ceramics

Dual-phase (alpha+beta)-Si3N4 ceramics with MgO-RE2O3 and SiO2-RE2O3 (RE = La, Nd, Gd, Ho and Lu) complex sintering additives were prepared by SPS at 1650 and 1700 degrees C. The effect of sintering additives on the phase transition, microstructure evolution and mechanical properties of the Si3N4 ceramics were studied. For the MgORE2O3 samples, as the RE radius increased, the phase transition was decelerated, the percentage of rod-like grains and fracture toughness decreased and the hardness showed a hill-shape curve. It is proposed that the effect of RE radius is connected with the segregation behavior of RE cations on the surface of Si3N4 grains. For the SiO2- RE2O3 samples, as the RE radius increased, the phase transition was accelerated and the percentage of rod-like grains increased. It is suggested that the effect of RE radius is related with the liquid phase viscosity and nitrogen solubility.

Automated summary

Dual-phase (alpha+beta)-Si3N4 ceramics were prepared by SPS with MgO-RE2O3 and SiO2-RE2O3 as sintering additives. The effect of additives on the phase transition, microstructure evolution, and mechanical properties of Si3N4 ceramics were investigated. The results showed that the type and RE radius of additives have significant influences on the properties of Si3N4.