Mechanical properties and thermal conductivity of dense β-SiAlON ceramics fabricated by two-stage spark plasma sintering with Al2O3-AlN-Y2O3 additives

Abstract Fully dense β-SiAlON ceramics with excellent mechanical properties and good thermal conductivity were fabricated by two-stage spark plasma sintering (SPS) processes without and with applying pressure respectively, using α-Si3N4 powder and 6 Al2O3-3 AlN-6 Y2O3 (in wt.%, label with 636), 424 and 422 additives. In the first stage SPS process without pressure, the relative dense β-SiAlON ceramics with interlock microstructures of elongated grains and density of 3.14∼3.18 g cm-3, hardness of 14.00∼14.82 GPa and fracture toughness of 6.00∼6.63 MPa.m1/2 were obtained by sintering at about 1600 °C for 20 minutes. In the second stage SPS process at about 1425 °C for 5 minutes under pressure of 24 MPa, the fully dese β-SiAlON ceramics with density of 3.22∼3.24 g cm-3, high hardness of 15.68∼15.95 GPa, high fracture toughness of 6.38∼7.03 MPa.m1/2 and thermal conductivity of 13.5∼19.6 Wm-1K-1 were obtained. The reaction between the samples and the graphite mold can be avoided in this fabrication method.