Influence of powder mixing processes on phase composition, microstructure, and mechanical properties of α/β-SiAlON ceramic tool materials

Abstract α/β-SiAlON composite ceramics using powders mixed through different processes were prepared via spark plasma sintering. Effects of different powder mixing methods (ball-milling and ultrasonic vibration with mechanical stirring), ball-milling media (Al2O3 and Si3N4 balls), and mixing times (12 and 24 h) on the components and morphology of mixed powders, phase composition, microstructure, and mechanical properties of α/β-SiAlON ceramics were studied. Results indicate that additional oxides are mixed to powders when ball-milled with Al2O3 balls, leading to an increase in the amount of amorphous glass and a decline in α/β ratio and mechanical properties. These effects were reduced when powders were ball-milled with Si3N4 balls, and α-SiAlON content and fracture toughness increased significantly. Moreover, α/β-SiAlON ceramics that underwent ultrasonic vibration with mechanical stirring exhibited the highest hardness and oxidation resistance at high temperature, and their α/β ratio was close to expected value.