High-performance B4C-LaB6 composite ceramics fabricated via hot-pressing sintering with La2O3 as sintering additive

The B₄C-LaB₆ composite ceramics were fabricated via hot-pressing sintering at 2050 °C and 20 MPa pressure with the mixture of boron carbide (B₄C) and 2–5 wt% lanthanum oxides (La₂O₃) as raw materials. The effects of additive La₂O₃ content on the microstructures and mechanical properties of composite ceramics were investigated, and reaction mechanisms of La₂O₃ and B₄C at different temperatures were studied in detail. La₂CO₅, La₃BO₆ and LaBO₃ were formed by the reactions of La₂O₃ and B₄C at different temperatures, and finally LaB₆ was formed below 1600 °C. The comprehensive mechanical properties of B₄C-LaB₆ composite ceramics were optimized by adding 4 wt% La₂O₃, the flexural strength, fracture toughness and Vickers hardness reached 350 MPa,4.92 MP am^1/2 and 39.08 GPa, respectively. The high densification and flexural strength of composite ceramics achieved in the present study were attributed to LaB₆ hindering the movement of grain boundary. However, the densification was reduced caused by CO as La₂O₃ content increased to 5 wt%. The fast channel was formed via B₄C reacting with La₂O₃, which accelerated migration of B₄C in the sintering process. The content of La₂O₃ played an important role in the fracture mode of the composite ceramics, and ultimately affected the fracture toughness of the composite ceramics.