B <sub> 4 </ Sub> C Ceramic Composites Preparation

Boron carbide (B₄C) ceramics has been recognized as one of the important and promising engineering ceramics due to its is widely used in wearable materials, light bombproof armor and space flights etc because of its excellent physical and chemical properties, for instance, super-hardness (HV>30MPa), high melting point (2450℃) and low density (2.52g/cm³). And now it is widely used in bulletproof materials, radiation protection materials, lubricate materials, wearable materials, sharpener materials and shield materials etc. However, because of the strong covalent bond , Boron carbide is difficult to be sintered. When Boron carbide is sintered at 2300℃ in normal atmosphere, the density only can get to 80%, furthermore the mechanical properties are not perfect, so , it cannot satisfied the engineering demands.In this paper, reactive hot-pressing (RHP) is used to prepare light-duty B₄C matrix composites ceramics at a relatively lower temperature by adding activation additives (Al₂O₃, Si, (Ti,W)C) into B₄C matrix. B₄C is reinforced and flexed by the generation of SiB₆ in suit. To improve the fracture toughness of the B₄C composites by adding whiskers.XRD, SEM technologies are used to detect the microstructure and the phase. Mechanical properties are measured by micro-indentation, three-point bending methods. The analysis shows: Al₂O₃ can be used to low the sinter temperature, and it can improve the flexural strength. When the weight of Al₂O₃ under 10%, the hardness of B₄C composite ceramics is hardly influenced. The adding of (Ti,W)C can increase the fracture toughness of B₄C composite ceramics due to the forming of TiB₂ and W₂B₅, which can create the mismatch of heat expansions. The adding of Si can low the sinter temperature obviously, at the same time, the mechanical properties of B₄C are increased because of the generation of SiB₆ in suit.The cracking mode of B₄C matrix composites ceramics is the combination of inter-granular fracture and trans-granular fracture. And the former is mainly. The reinforced-toughened factors include fine-grain, whiskers, plate-like structure, special scattering phases and residual thermal stress.