Local chemistry changes in Si₃N₄ based ceramics during hot-pressing and subsequent annealing

The local chemistry changes within the triple points of the Si₃N₄ based ceramics are discussed. The extents of Fe, Cr and Ti impurities segregation and coalescence after crystallization of the triple point were determined. These impurities were present also prior to crystallization in the glassy triple pockets but they were distributed over the whole volume of the triple pockets and were thus under the detection limits of the EDX method. The paper indicates that these coalesced impurities are responsible for cavity formation in the Si₃N₄ based composites studied.