Investigation of Microstructure and Thermal Shock Resistance of the B<sub>4</sub>C/BN Composites Fabricated by Hot-Pressing Process

Abstract

The B4C/BN composites were fabricated by hot-pressing process. The B4C/BN composites included the B4C/BN microcomposites and B4C/BN nanocomposites. The B4C/BN microcomposites were fabricated by hot-pressing process, and the B4C/BN nanocomposites were fabricated by chemical reaction and hot-pressing process. In this research, the phase composition, microstructure, mechanical property and thermal shock resistance of the B4C/BN microcomposites and B4C/BN nanocomposites were investigated. The B4C/BN microcomposites and the B4C/BN nanocomposites exhibited the homogenous and compact microstructure, and the h-BN particles were homogenously distributed in the B4C matrix. The mechanical property of the B4C/BN microcomposites and B4C/BN nanocomposites decreased gradually with the increase of h-BN content, but the B4C/BN nanocomposites exhibited the higher mechanical property than that of the B4C/BN microcomposites. The thermal shock resistances of the B4C monolith and the B4C/BN composites were measured by water-quenching method. The thermal shock resistances of the B4C/BN microcomposites and the B4C/BN nanocomposites were remarkably improved in comparison with the B4C monolith. The thermal shock resistance of the B4C/BN nanocomposites was much better than that of the B4C/BN microcomposites. The thermal shock temperature difference (ΔTc) of the B4C monolith was about 300oC, the ΔTc of the B4C/BN microcomposites was about 500oC and the ΔTc of the B4C/BN nanocomposites was about 600oC. The B4C/BN composites exhibited the high thermal shock resistance due to the high fracture strength and low elastic modulus. The microstructure showed that the weak interface of B4C/BN and cleavage behavior of laminate structured h-BN particles would remarkably improve the thermal shock resistance of the B4C/BN composites.