The Thermodynamics And Kinetics Analysis Of In Situ Al₂O₃-TiC_p/Al Composites Fabricated By Melting And Casting

By means of differential scanning calorimeters (DSC) and scanning electronic microscope and energy dispersive spectrum (EDAX) and X-ray Diffractometer(XRD) etc., the thermodynamics and kinetics of a serial of synthetical reactions in Al-TiO₂-C system were analyzed, and the kinetic model for reactive mechanisms of the in situ Al₂O₃-TiCp/Al composites made through melting and casting technique, and the fabrication processes of the composites were formulated. Meantime, the influences of rare earth oxide CeO₂ on the shape and size and distribution and quantity and microstructures of in situ Al₂O₃-TiCp/Al composites were investigated.The calculated results show that the in situ Al₂O₃-TiCp/Al composites can be obtained by controlling temperature and other technological parameters from the thermodynamics, and avoidable of existence of harmful Al₄C₃ and Al₃Ti phases. The kinetic mechanism is composed of melting and diffusion and reaction and cooling stages for the fabrication of in situ Al₂O₃-TiCp/Al composites. The main chemical reactions in the Al-TiO₂-C system consist of both formation Al₂O₃ particles which Al replaces Ti atom and TiC particles which the graphite and react with its rich Ti layer with a release of strong heat. The kinetic model of Al₂O₃-TiCp/Al composites by melting case was firstly established. The kinetic analysis revealed that the finer the graphite and TiO₂ powder and mixture, the larger the volume fraction of reinforcements, and the more the rate of the chemical reactions.The experimental results present that the in situ Al₂O₃-TiCp/Al composites with disperse, submicro in size, distributed homogeneously have been successfully fabricated. The adding of rare earth oxide CeO₂ reduce the Gibbs free energy and reactive temperature, shorten the reactive period, improve the microstructures of in situ Al₂O₃-TiCp/Al composites further.