Foundational Research On SHS Of Al₂O₃-TiC-Al Composites Under The External Electric Field

Self-propagating High-temperature Synthesis (SHS) technology is widely used to prepare metal-ceramics composites because it has the characteristics of conserving energy, fast reaction and high product purity. However the synthetized composites have high porosity (20%-50%), which prohibits its use as structural material. So SHS-densificating is one of the focuses in SHS research field. In addition, this technology is only suitable for high heat releasing reaction system due to the thermodynamic limitation of SHS reaction. Therefore, it's also a developmental direction of SHS technology how to induce the self-propagating combustion of this reaction system with thermodynamic limitation of SHS reaction. In this thesis, TiO₂-C-Al reaction system was used to synthesize relatively dense Al₂O₃-TiC-Al composites by the filling and welding of liquid Al formed during SHS process. The results show that the compactness of the synthetized composites is improved with the increasing of excess Al content in the system. But when the excess Al content was more than 10mol, SHS reaction of the system was hard to take place. So, an external electric field was used to activate the system with an excess Al content of 14mol. As a result, the SHS reaction was taken place under the external electric field, and an Al₂O₃-TiC-Al composite with a relative density of 92.5%. was successfully synthesized. In addition, the SHS reaction thermodynamics under the electric field was analyzed and the corresponding mathematic model was also set up. In addition, the effects of the electric field on the SHS process and the microstructures of the composites have been studied. The result shows that the Joule heat effect of electric field improves the initial temperature of the rlative system, and, theforefore, can break through the restriction of SHS thermodynamics. When the strength of the electric field is greater than 7.5 v/cm, the SHS reaction of the system with an excess Al content of 14mol can take place. Moreover, with the increase of the strength of the electric field, the needed ignition time is decreased, whereas the combusion temperature and combustion wave propgating speed is increased. As a result, the size of the synthesized Al2O3 and TiC particles has been decreased, while the relative density of the synthesized Al2O3-TiC-Al compnsites have been improved. So, the electric field activated SHS technology is a new way to prepare dense metal-ceramics composites.