Microstructure and mechanical properties of highly dense Si3N4 ceramics with ZrN–AlN–Re2O3 (Re=Yb, Y, Nd, Ce, La) additives

The Si3N4 ceramics with ternary ZrN–AlN–Re2O3 (Re=Yb, Y, Nd, Ce, La) and ZrN–AlN system as sintering additives were prepared by hot-pressed sintering with vacuum environment at 1750°C-30min–30MPa. Subsequently, the effect of the ternary additives system with 2 wt% Re2O3 on phase transformation, grain boundary phases, microstructure, and mechanical properties of the Si3N4 ceramics were investigated firstly. All samples achieved the high β-Si3N4 phases transformation (≥98.86%), while the grain boundary phases RexZr1-xO(4-x)/2 and Yb2Si2O7 were detected in the sintered Si3N4 ceramics with Re2O3 additives. Additionally, compared with Si3N4 ceramic not contain Re2O3 additives, the Si3N4 ceramics added Re2O3 additives presented the textured microstructure with more elongated rodlike β-Si3N4 grains based on the XRD and SEM results. Consequently, the sample S-Ce with added CeO2 additive shows the highest relative density of 99.85% and optimal fracture toughness of 8.75 ± 0.36 MPa m1/2. The sample S–Nd with added Nd2O3 additive presented a highest bending strength of 1061.78 ± 41.76 MPa. Sample S–Yb with added Yb2O3 additive presented the maximum Vickers hardness of 16.35 ± 0.07 GPa. The results of this study can provide a helpful reference for the preparation of high-performance Si3N4 ceramics.