Preparation,Microstructures,and Mechanical Properitied Of New Bilayer Bulletproof TiB₂/B₄C-Al/B₄C Composite

B4C is considered as one of the best bullet proof armor materials in a number of bullet proof ceramics on account of its outstanding properties, such as high hardness, high melting point, and low density, etc. But, B4C’S low toughness not only greatly reduces its ballistic resistance, but also makes it uncapable of resisting the impact of multi-bullets. In order to improve the toughness and the ballistic resistance of B4C ceramics, researchers have proposed many feasible ways, such as fibers (whiskers), second-phase particles or laminating reinforcement, etc. However, reports on the abovmenttioned methods to strengthen B4C are still limited. Therefore, with respect to the disadvantages in toughness of B4C, this work aims to develop a novel kind of bilayer TiB2/B4C-Al/B4C composite. The microstructures and mechanical properties of such bilayer bullet proof material will also be studied, including the interface between two layers, which is believed to be crucial for the bullet proof performance.B4C, TiO2, Al alloys and C were used as raw materials in this experiment. After the mixing of compound powders manually or by mechanical ball-milling method, the samples were subject to drying, granulation, and molding under5.66MPa pressure. Hot pressing of obtained laminated TiB2/B4C-Al/B4C porous discs was carried out at1900℃followed by vacuum infiltration of aluminum at1100℃. The resulting bilayer TiB2/B4C-B4C will be examined and tested by different means.The experiment results show that:the synthetic conditions, e.g. sintering and Al infiltration temperature, heating ramp, etc., are demonstrated to be crutial for the fabrication of bilayer TiB2/B4C-Al/B4C composite. Based on the preparation of layered material, the optimized fabrication conditions was:1500℃×1h+1900℃×1h and700℃×30min+1100℃×40min for the sintering and vacuum infiltration of aluminum process, respectively. Under such conditions, the infiltration of aluminum into the porous B4C in AI/B4C layer and highly densified Al/B4C layer up to95.8%(relative density) could be realized. By means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy, the characterization results show that:The interface did not be observed in the such bilayer TiB2/B4C-Al/B4C composite; Al and B4C react in the interface to generate the Al3BC phase at temperatures lower than1100℃; the TiB2and B4C phase, Al and B4C phase combined well as confirmed by high-resolution TEM.The mechanical properties of the bilayer TiB2/B4C-Al/B4C composite were tested based on two surfaces (top and bottom).The results show that the flexural strength was206.0MPa and416.3MPa using TiB2/B4C layer and Al/B4C layer as the bearing surface, respectively; When the incision was opened on the TiB2/B4C layer and Al/B4C layer, the fracture toughness was4.8MPa-m1/2and4.7MPa-m1/2, respectively; and The vickers hardness of Al/B4C was32.3GPa, and the rockwell hardness (HRA) of TiB2/B4C was72.1.