Kurt Kugler, Ivan Ravlich, Mark I. Jones:
Effects of amount and type of cation species on the phase formation of single and codoped a-SiAlONs
Journal of Materials Science, 2012, 47(3), 1205-1216
The phase formation of single phase a-SiAlON ceramics based on a-Si3N4 was investigated using different rare earth (RE) or metallic cations to stabilise the a-phase. The effects of sintering temperature, size and type of stabilising cation and the addition of extra liquid forming additives on the phase transformation of a-Si3N4 to a-SiAlON were considered. The influence of the chosen parameters on properties such as density and hardness is furthermore discussed for Ca-codoped silicon aluminium oxynitride (SiAlON) ceramics (50% RE cations combined with 50% calcium cations). For smaller and larger RE systems different intermediate phases occur and the dissolution of sintering additives takes place at different temperatures, resulting in different amounts of SiAlON at a given sintering temperature. For smaller cations, the SiAlON formation is favoured below 1750°C compared to larger cations. The addition of extra liquid to the starting composition supports the SiAlON formation above the eutectic temperature. Contrary to the RE systems the calcium-doped samples did not show an intermediate phase during sintering. The cation solubility for sintering additives is higher and therefore the amount of SiAlON created below 1750°C increased. The final amount of SiAlON at 1850°C was about the same for all systems. Mechanical properties are also influenced by the composition of the starting powder. In general, increasing temperature leads to higher density and hardness.
SiAlON, Sintering, Sintering additives, Microstructure, Rare earths, Phase Formation