Densification and Mechanical Properties of Monolithic B4C and In-Situ Formed TiB2 Containing B4C–TiB2: Effects of Particle Size and Impurity

This study investigates the effects of particle size, powder purity, and in situ TiB2 formation on the densification behavior and mechanical properties of B4C-based ceramics fabricated via spark plasma sintering (SPS). The results demonstrate that particle size is the dominant parameter controlling densification and microstructural evolution. An intermediate particle size (F1200) yields the highest relative density (98.41%) and superior mechanical properties, including a hardness of 33.34 GPa and fracture toughness of 4.63 MPa·m1/2, by providing an optimal balance between diffusion kinetics and particle packing. The in situ formed TiB2 significantly enhances fracture toughness compared to monolithic B4C. Among the composite samples, the medium particle size containing BT1200 exhibits the best overall combination of properties, with a relative density of 98.00%, hardness of 25.40 GPa, and fracture toughness of 5.18 MPa·m1/2. The highest fracture toughness is achieved in the largest particle size containing BT325 (6.29 MPa·m1/2), confirming the effectiveness of TiB2 combined with large particle size as a toughening phase. Although higher powder purity contributes to improved phase homogeneity, its influence on densification and mechanical performance is secondary compared to particle size and pore evolution. Excessive particle refinement leads to residual porosity, limiting full densification. Overall, optimizing particle size together with controlled in situ TiB2 formation is essential for achieving high-performance B4C-based ceramics and composites. These findings provide a practical framework for tailoring microstructure and mechanical properties in advanced ultra-hard ceramic systems.