Simultaneous Improvement of Strength, Hardness, and Toughness in B4C–TiB2 Composites Through Dual-Grain Size Design

Boron carbide (B 4 C) ceramics exhibit exceptional hardness and low density, making them promising candidates for structural applications in extreme environments. However, their widespread adoption is hindered by poor sinterability and low fracture toughness. Balancing hardness, strength, and toughness in B 4 C ceramics remains a significant challenge owing to the inherent trade-offs among these properties. To overcome this, a fine and uniform dual-grained B 4 C–TiB 2 composite was fabricated by in-situ reactive sintering of TiO 2 , graphite, and a bimodal B 4 C powder. A two-step ball-milling process during powder preparation was pivotal in eliminating TiB 2 agglomeration and ensuring microstructural homogeneity. The resultant composite achieved a synergistic enhancement in flexural strength (786 ± 51 MPa), fracture toughness (5.66 ± 1.44 MPa·m 1/2 ), and Vickers hardness (35.5 ± 1.1 GPa). The high strength and hardness are attributed to pronounced grain refinement and low open porosity. The enhanced toughness originates from synergistic mechanisms: crack-inhibiting compressive residual stress and transition to a mixed transgranular/intergranular fracture mode facilitated by locally concentrated sub-micron B 4 C grains. It is demonstrated that grain-size engineering by powder design is a viable strategy for developing lightweight ceramic composites with a superior balance of strength, hardness, and toughness.