The effect of the wet-milling process on sintering temperature and the amount of additive of SiAlON ceramics

In this study, nano-sized SiAlON powders were produced by wet milling at elevated speeds as a top-to-bottom process. Before the milling process, different milling times and mediums were performed for the determination of the most efficient milling system. The milled powders were characterized by BET and X-ray diffraction (XRD) measurements and the results were compared to standard samples. The standard powders were produced using a conventional process (the ball to powder ratio was 1:1.5, at 300 rpm, for 1.5 h) having a few hundred nanometer particle size. The nano powders were milled using a wet-milling process in an optimum medium so that the particle size was decreased down to ≈70 nm. The samples, produced from the nano powders, were densified at 150 °C lower degrees than the sintering temperature of samples which were produced by a conventional method (185 nm). However, the phase transformation of α → β-SiAlON was also observed related to the amount of additives. This transformation affected the mechanical properties of the SiAlON ceramic. The results were discussed using the relationship between density, phase composition, microstructure and mechanical properties.