Mullite/molybdenum ceramic-metal composites

Dense (> 98 th%) homogeneous mullite/Mo (32 vol.%) composites with two different Mo average grain sizes (1.4 and 3 mu m) have been obtained at 1650 degrees C in vacuum and in reducing condition. Depending on the Mo grain size and processing atmosphere, the K-1C ranges from 4 to 7 MPa m(1/2) and sigma(f) from 370 to 530 MPa. The MoO2-2SiO(2). 3Al(2)O(3)-Mo system was found to be compatible in solid state, and a solid solution of approximate to 4 wt% of MoO2 in mullite at 1650 degrees C was detected. A solid slate dewetting of MoO2 from the surface of the Mo particle takes place during sintering. It was found that the absence of MoO2 in the mullite/Mo composites by processing in reducing conditions increases the strength of the metal/ceramic interface and the plasticity of the Mo metal particles, thus strengthening the composite by a crack bridging mechanism. As a result, the K-1C and the sigma(f) values of the ceramic-metal composite were found to be approximate to 4 times and approximate to 2 times higher than the ones corresponding to the mullite matrix. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.