Research On Microstructures And Mechanical Properties Of B₄C/Al Composites By Pressureless Infiltration Process

Boron carbide (B4C) ceramics is a promising material with unigue properties such as extremely high hardness, low density, excellent resistance to chemical attack as well as high capability for neutron absorption. Boron carbide-aluminium (B4C/Al) composites inherit the excellent performance of boron carbide and aluminium, overcoming boron carbide’s extreme susceptibility to brittle fracture. B4C/Al composites were produced by pressureless melt infiltration of2024A1alloys into porous B4C compacts. The in situ synthesized TiB2and CeB6added to the porous B4C compacts were improved the microstructures and mechanical properties of B4C/Al composites. The heat-treatments of B4C/Al composites were also researched. Mechanical properties of B4C/Al composites were characterized by testing of hardness, bending strength and fracture toughness. The relationship between microstructures and mechanical properties of B4C/Al composites were investigated by using optical metallography (OM),X-ray diffraction (XRD), scanning electron microstructure (SEM), electron microprobe analysis(EMPA).The result showed as follows:(1)The porous B4C compacts prepared by pressureless presintering have three-dimensional skeleton structure with the porosity of40%or more.Metal oxide and B4C reacted in situ reaction as follow:2TiO2+B4C+3C�'2TiB2+4CO↑;2CeO2+3B4C+C�'2CeB6+4CO↑(2) B4C/A1composites were produced by pressureless melt infiltration prossess superior mechanical properties, with the value of57.25HRA,400.8MPa,6.09M Pa·m1/2respectively.(3) The in situ synthesized TiB2and CeB6improved the bending strength and fracture toughness of composites significantly. The bending strength and fracture toughness of B4C-TiB2/Al and B4C-CeB6/Al composites reached431MPa,8.28MPa-m1/2,52HRA and444MPa,7.47MPa·1/2,50HRA, respectively.(4)The main phases of B4C/A1、B4C-TiB2/Al、B4C-CeB6/Al composites include a (Al)、B4C、Al3BC and AlB2The microstructures of the composites were improved after heat-treatments. More Al3BC and AlB2phases were generated from the enormous consumption of B4C and a (Al). The phases B4C were finer and more equiaxed owning to aluminum liquid erosion.(5) Insulated in700℃for36h, the value of hardness, bending strength and fracture toughness of B4C/A1composites were71.1HRA,381.6MPa,6.58MPa·m1/2, respectively. The mechanical properties of B4C-CeB6/Al composites were66.2HRA,416MPa and6.6MPa·m1/2by being insulated in the optimal heat-treatment process.