Synthesis and characterization of MgAlON–BN composites

Abstract

Abstract In the present paper the Gibbs energy of formation of MgAlON was evaluated, and on this basis the phase stability diagram of Mg – Al – O – N – B was established. Dense magnesium aluminium oxynitride – boron nitride (MgAlON – BN) composites with 0 – 30 vol.% BN were synthesized by hot pressing in the temperature range 1750 – 1850 °C in the phase stability region. The phase compositions of the composites analyzed by X-ray diffraction indicated that the main phases were MgAlON and h-BN and no impurities were found. The microstructures of the composites analyzed by transmission electron microscopy, scanning electron microscopy, and high-resolution electron microscopy showed that the MgAlON did not react with BN, and the latter was distributed on the grain boundary of MgAlON homogeneously. Excessive BN (> 20 vol.%) resulted in a discontinuous microstructure for MgAlON. A matrix-flushing method was employed in the quantitative X-ray diffraction analysis for the multi-component MgAlON – BN composites. The results showed that the relative MgAlON content decreased in the process of sintering MgAlON – BN composites. Thermodynamic analysis showed that some Al2O3, AlN, and MgO escaped under the reaction conditions. The lattice parameters of MgAlON in the composites have also been evaluated.