A Hew Mechanical Activation assisted Self-Propagating High-Temperature Synthesis of Metal Carbide-Boride Composites

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Boride and carbide of zirconium show a number of excellent properties such as high melting temperature, high strength, high thermal and electrical conductivity, and chemical stability. Therefore, the use of these ceramics in composites can be expected to offer potential candidates for a variety of high-temperature structural applications. In order to prepare the powder mixtures of ZrB_2 and ZrC with fine, homogeneous microstructure, we have developed mechanical activation assisted self-propagating high-temperature synthesis (MA-SHS) in air, and successfully applied to the synthesis of carbides and nitrides of Al,Zr and Nb, and borocarbides of Al_3BC. When the powder mixtures of Zr/B/O=3/2/2〜6/10/1 in molar ratio were mechanically activated (MA) by ball milling and then exposed to air, they self-ignited spontaneously and the self-propagating high-temperature synthesis (SHS) was occurred to form ZrB_2 and ZrC simultaneously. In this MA-SHS process in air, it was found to be essential that graphite is converted into finely divided, disordered carbon by mechanical activation and mixed with the particles of Zr and B in an intimate contact state. In addition, the ZrB_2-ZrC composites were produced from these MA-SHS powder mixtures by spark plasma sintering (SPS) at 1800℃ and showed the values of Vickers hardness of 17.8 GPa for the MA-SHS powder compact of Zr/B/C=2/2/1 and fracture toughness of 5.1 MPa m^<1/2> for the one of Zr/B/C=4/6/1.