Fabrication and wear behaviors of graded Si3N4 ceramics by the combination of two-step sintering and beta-Si3N4 seeds

摘要

Graded Si3N4 ceramics with sandwich-like microstructure were fabricated by the combination of hot-pressing, spark plasma sintering and beta-Si(3)N(4)seeds.Phase compositions, microstructures, mechanical properties, and wear behaviors were investigated. Main alpha-S1(3)N(4) phase were detected in the outer layers, and only beta-Si3N4 phase were observed in the inner layers. The outer layer with ultra-fine equiaxed grains were well bonded to the inner layer with a distinct bimodal grain size distribution. Vickers hardness of outer layer (similar to 21.2GPa) was much higher than that of inner layer (similar to 16.1 GPa), whereas fracture toughness of outer layer (similar to 3.5MPam(1/2)) was much lower than that of inner layer (similar to 5.9 MPa m(1/2)), indicative of the hard surface and tough core. Due to the ultrafine microstructure and high hardness of outer layer, the graded Si3N4 ceramics exhibited superior wear resistance with low wear rate.