Mechanism and microstructural evolution of combustion synthesis of ZrB2–Al2O3 composite powders

Mechanism of combustion synthesis (CS) of ZrB2–Al2O3 composite powders was systematically analyzed by a combustion front quenching method (CFQM). The microstructural evolution during the CS process was investigated by field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectrometer (EDS). The combustion temperature and wave velocity were measured by the data acquisition system. Moreover, the phase constituents of the final product were examined by X-ray diffraction (XRD). The thermal behaviors of the stoichiometic powders under the thermal exposure were characterized using differential scanning calorimetry (DSC) and thermogravimetric (TG). The results showed that the combustion reaction started from the melting of the B2O3 and Al particles, which was followed by the formation of ZrO2–B2O3–Al solution. The ignition temperature of this system was determined to be around 800 °C. B and Al2O3 were then precipitated from the solution. As the CS reaction proceeded, Zr and Al2O3 were produced by the reaction between ZrO2 particles and Al and precipitated from the solution. ZrB2 could then be formed by the direct reaction between Zr and B. Finally, the ZrB2–Al2O3 composite powders were obtained. Furthermore, a model corresponding to the dissolution–precipitation mechanism was proposed.