The Effect Of Process Parameters On The Formation Of ZrB₂-Al₂O₃ Composite By SHS

In this paper, Zr B2-Al2O3 composite was successfully prepared by Self-propagating High-temperature Synthesis(SHS) using exothermic reactions in Zr O2-B2O3-Al system.Reaction free energy and adiabatic temperature in Zr O2-B2O3-Al system have been theoretically calculated and analyzed. The physical and chemical changes in the reaction process were studied by differential scanning calorimetry analysis(DTA). The effect of argon pressure, Zr O2 particle size and Al particle size on combustion parameters, phase constituents and microstructural characterization were studied in details.According to the thermodynamics theories, adiabatic temperature and reaction free energy in Zr O2-B2O3-Al system have been theoretically calculated and analyzed.Results of adiabatic temperature calculation showed that the adiabatic temperature of Zr O2-B2O3-Al system was 2327 K, which is higher than 1800 K, so the system can be self-propagating. The reaction of B2O3-Al, Zr-B and Zr O2-B2O3-Al would occer in the studied temperature range(27℃-2027℃), because their reaction free energy were lower than zero. The reaction of Zr O2-Al would occer below 700 ℃. Differential thermal analyzing(DTA) was used to analyze the physical and chemical changes in the reaction process. B2O3 melted in 450℃, then Al melted in 665℃, the three phase reaction was taken palce from 800℃. B2O3 reacted with Al at first, then Zr O2 reacted with Al, the reaction of B and Zr were occured finally.Argon pressure had an important effect on combustion temperature, phase composition and microstructure. The evaporation of B2O3 was suppressed as the increase of argon pressure. When the argon pressure was 1.5 MPa, the combustion temperature was the highest, the the final products were only Zr B2 and Al2O3 phases and the microstructure were more homogeneous.The effect of Zr O2 particle size and Al particle size on combustion parameters,phase composition and microstructure were studied. Combustion temperature and combustion velocity decreased as the increase of Zr O2 particle size. When the Zr O2 particle size was 3μm,the combustion temperature and combustion velocity were the highest, the the final products were only Zr B2 and Al2O3 phases and the the microstructure were more homogeneous. Similarly, when the Al particle size was 48μm,the combustion temperature and combustion velocity were the highest, the the final products were only Zr B2 and Al2O3 phases and the the microstructure were more homogeneous. Therefore, under trial conditions, the optimum parameters were: argon pressure was 1.5MPa, the Zr O2 particle size was 3μm and the Al particle size was48μm.