Differing Effects of Mn and Mg Oxide Sintering Aids on Sialon Creep and Fracture

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This study is based on two sialon ceramics hot-pressed with small amounts of two different sintering additives, MgO and Mn3O4. The grain boundary interfaces were characterized by high resolution electron microscopy and Auger electron spectroscopy.

The major microstructural difference between the two ceramics was the occurrence of microscopic regions of triple junction silicate glass in the Mn containing ceramic. High temperature creep studies of this ceramic showed cavitation induced deformation. In contrast there was no detectable interfacial silicate phase in the Mg containing ceramic and no cavitation was observed during high temperature deformation.

Furthermore, microstructural observations revealed that long duration heat-treatment of the Mn containing ceramic resulted in reduction of triple junction glass beyond detection. This desegregation of impurities led to non-cavitating deformation and hence resulted in marked improvement in creep and slow fracture resistance.

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