Liquid formation in the Y-Si-Al-O-N system

Some silicon nitride ceramics are sintered using a combination of ¥203 and A12U3 additives to .form a Y-Si-Al-O-N liquid that promotes densification and allows the α->β transformation to take place by solution/precipitation through the liquid which cools as an intergranular phase. The type and amount of additive determines the nature and quantity of the resulting grain boundary phase as indicated and this can affect high temperature strength, creep resistance and oxidation resistance. Thus it is important to understand the phase equilibria in these complex systems and then apply this knowledge to processing, the development of beneficial microstructures and the relationship between these and properties. One difficulty is that, for any particular composition, the quantity and composition of the liquid at the sintering temperature is not known accurately and a full compositional representation has not been achieved.