The improvement mechanism of mechanical properties of B4C ceramics by constructing core-shell powders

B4C ceramics have been widely used in armor plate and cutting tools due to their high hardness. However, their poor sintering performance and low fracture toughness have limited their extended applications. In order to solve these problems, B4C@TiB2 composite powders with core-shell structure were prepared by a sol-gel method using B4C and TiCl4 as raw materials and then sintered by spark plasma sintering. The composite powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The mechanical properties of B4C ceramics were tested by indentation and three-point bending methods. The results showed that the B4C@TiB2 composite powders exhibited a tight core-shell structure, and the chemical bonds on the surface were mainly B-C and B-Ti bonds. When the molar ratio of B4C:TiCl4 was 2:1, the relative density and bulk density of B4C ceramics reached 96.2% and 2.92 g/cm(3), respectively. Because of the good sintering performance of the B4C@TiB2 composite powders, the Vickers hardness and fracture toughness reached 26.6 GPa and 5.22 MPa m(1/2), respectively. The bending strength reached a maximum of 570 MPa. The excellent fracture toughness can be attributed to crack deflection, crack branching, and the residual thermal stress of the core-shell structure.