Preparation, sintering behavior, and microstructural studies of Al2O3/Mo composites from boehmite-coated Mo powders

Boehmite-coated Mo powders were prepared by controlled hydrolysis of aluminum sulfate in the presence of urea. The structure and chemical composition of coated powders were investigated with various approaches. The results showed that uniform and compact boehmite layers were successfully deposited on the surfaces of Mo particles. Differences between the infrared spectrum of the as-prepared coated powder and that of the pure boehmite suggested that there was a strong chemical bond at the interface between the boehmite layer and Mo particle. The hot-press sintering of the coated powders showed that the relative density of sintered specimens increased with sintering temperature below 1400 degreesC, and decreased with Mo content up to 15 vol%. In the latter case, the sintering of Al2O3/Mo composites was impeded by large agglomerates of Mo particles, and MoO2 phase in the calcined powders. Microstructural observations of composites revealed that most Mo particles were located at the triple junctions of alumina grains, and only those particles smaller than 500 nm could be trapped in the alumina grains. The existence of microcracks and strain fringes was clearly observed, and was attributed to the thermal expansion mismatch between alumina and molybdenum. (C) 2001 Elsevier Science Ltd. All rights reserved.