Microstructures and mechanical properties of fast hot pressure sintered B₄C-SiC-NbB₂ composites using a novel Nb₂Si sintering aid

B₄C ceramic is regarded as a fascinating material in many engineering applications, yet its wide applications are restricted by poor sinterability and intrinsic brittleness. Hence, NbSi₂ was first proposed as a reactive additive for the generation of B₄C ceramics. The high-performance B₄C-SiC-NbB₂ composites were successfully prepared at a relatively low temperature via an in-situ reaction of B₄C and NbSi₂. The impact of NbSi₂ content on the densification behavior, phase composition, microstructure and mechanical properties of composites was investigated. The results indicated that the proper addition of NbSi₂ promoted densification and enhanced the mechanical properties via transient liquid-phase sintering. When the NbSi₂ content was 20 wt%, the obtained B₄C-SiC-NbB₂ composites possessed attractive combination of properties, with the density, Vickers hardness, flexural strength, and fracture toughness reaching 98.72 %, 34.05 ± 0.46 GPa, 708.5 ± 23.1 MPa and 4.78 ± 0.2 MPa m^1/2, respectively. The appearance of reinforced second phase particles, the existence of mixed intergranular/transgranular fractures and the formation of residual stress induced crack deflection, crack branching and crack bridging, which made the crack propagation path more tortuous. Furthermore, the agglomerates composed of interlocked SiC and NbB₂ as a toughening structure were observed inside the B₄C matrix. These synergetic strengthening mechanisms consumed more fracture energy, which was responsible for the improvement of mechanical performance.