Study On Fabrication And Properties Of B₄C/Al₈B₄C₇ Composite

As a kind of high-performance structural ceramic materials, boron carbide shows excellent properties, such as low density, high melt-point, high hardness, high modulus, well chemical stability and strong neutron absorption ability. However, the strong covalent bond makes boron carbide difficult to be sintered. The high sintering temperature and low fracture toughness restricts the boron carbide in practical application.With two groups of different raw materials, e.g., Al, B₄C, C or Al, B₂O₃, C, Al₈B₄C₇ were prepared by self-propagation and pressureless sintering, respectively. The action of source of boron and processing factors on the Al₈B₄C₇ powder were studied. And the optimum sintering technique was discussed. Hot-pressure sintering process was adopted to prepare boron carbide ceramic materials by adding 5%, 10%, 15% and 20% Al₈B₄C₇or Al into B₄C powder, respectively. The adding amount of Al₈B₄C₇ or Al on the microstructure and mechanical properties of the material was investigated. Moreover, the toughening mechanism was discussed in this work. Moreover, the toughening mechanism was discussed in this work.The results indicated that Al₈B₄C₇ powder can be prepared from Al, B₄C, C raw materials by pressureless sintering method (1500℃, 1h). Al₈B₄C₇ or Al can both reduce the sintering temperature and be in favor of the sintering of boron carbide ceramic materials. The doping of Al₈B₄C₇ and Al significantly improve fracture toughness, when doping 20% Al₈B₄C₇, the fracture toughness was 5.53MPa·m^1/2, when doping 5% Al, the fracture toughness was 4.80MPa·m^1/2. The maximum strength, hardness and compressive strength were 508MPa, 27GPa and 1.73GPa, respectively. Analysis implied that crack deflection induced by thermal expansion coefficient mismatch, second phase toughening and microcrack toughening were responsible for the toughening mechanism.