Mullite/molybdenum composites

The possibility of fabricating continuous mullite/Mo FGMs with density closed to theoretical, by pressure slip casting of absolute ethyl alcohol based slurries has been shown. Dense (>98 th%) homogeneous mullite/Mo (32 vol %) composites with two Mo average grain sizes (1.5 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-IC ranged from 4 to 7 MPa.m(1/2) and sigma(f) from 370 to 530 MPa. The MoO2-2SiO(2).Al2O3-Mo were found to be compatible in solid state and a solid solution of approximate to 4 wt% of MoO2 in mullite at 1650 degrees C in argon atmosphere was detected. A solid state 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 plasticity of the metal particles strengthening the material by a crack bridging mechanism. Due to this fact, the K-IC 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 matrix.