Phase formation and microstructural evolution of R-α′-AlN-polytypoid ceramics (R=Y, Y+Sm and Sm)

In the present work, Y, Sm and (Y+Sm) were separately used to explore the effects of rare-earth elements on the reaction sequence and microstructural evolution in α-sialon-AlN-polytypoid composite ceramics. The results showed that the reaction sequences in the composite ceramics are affected by rare earth elements. With the existence of AlN-polytypoid α-sialon develops into elongated morphology. The Sm–α-sialon composition exhibits the feature of fine grains with high aspect ratio and Y-composition possesses rather coarse morphology with low aspect ratio. In the composite ceramics, AlN-polytypoid was not distributed homogeneously around the α-sialon grains, especially in the Y-composition. The variation in microstructure with rare-earth elements in the Sialon materials was discussed based on their reaction sequences.