Subsolidus phase relationships of the ß-sialon solid solution in the oxygen-rich part of the Nd-Si-Al-O-N System

The subsolidus phase relationships in the Nd2O3-Al2O3-SiO2 system and in the Si6-zAlzOzN8-z (0 less than or equal to z less than or equal to 4)-''Al2O3:AiN''-Al2O3-Nd2O3-SiO2-range of the Nd-Si-Al-O-N system have been determined. 50 three- and four-phase equilibria were established in this phase region. The phase equlibria define the regions of stable coexistence between beta-sialon Si6-zAlzOzN8-z (0 less than or equal to z less than or equal to 4) and oxide or oxynitride compounds, which are potential grain boundary phases for silicon nitride ceramics. beta-Si3N4 coexists with N-melilite (Nd2Si3-xAlxN4-x (0 less than or equal to x less than or equal to 1)), N-alpha-wollastonite NdSi2ON, a nitrogen-rich (Al, N)-apatite solid solution and Nd2Si2O7. Between 0 less than or equal to z less than or equal to 0.8 beta-siaIon Si6-zAlzOzN8-z) is compatible with N-melilite (Nd2Si3-xAlxN4-x (x = 1)), an (Al,N)-apatite of intermediate composition and Nd2Si2O7. The equilibrium phases between Z = 0.8 to z = 4 are NdAlO3 and the U-phase (Nd3Si3-xAl3+xO12+xN2-x) as well as NdAl11+xO18Nx (x 1) and corundum at the Al-rich terminal composition (z = 4).