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

Fully dense beta-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 alpha-Si3N4 powder and 6 Al2O3-AlN-Y2O3 (in wt.%, label with 636), 424 and 422 additives. In the first stage SPS process without pressure, the relative dense beta-SiAlON ceramics with interlock microstructures of elongated grains and density of 3.14(similar to)3.18 g cm(-3), hardness of 14.00(similar to)14.82 GPa and fracture toughness of 6.00(similar to)6.63 MPa m(1/2) were obtained by sintering at about 1600 degrees C for 20 min. In the second stage SPS process at about 1425 degrees C for 5 min under pressure of 24 MPa, the fully dese beta-SiAlON ceramics with density of 3.2(similar to)3.24 g cm(-3), high hardness of 15.68(similar to)15.95 GPa, high fracture toughness of 6.38(similar to)7.03 MPa m(1/2) and thermal conductivity of 13.5 (similar to)19.6 Wm(-1) K-1 were obtained. The reaction between the samples and the graphite mold can be avoided in this fabrication method.