| Boron carbide(B4C) ceramic is one of the most important special ceramics for its excellent properties. However, the widespread applications of B4 C ceramics, especially in the military field, have been restricted because of the low fracture toughness and the high sintering cost due to the chemical bond. In this paper, in order to promote sintering process and improve the mechanical properties of B4 C ceramics, Al-B2O3-C system which can trigger combustion synthesis reaction was initially introduced into the sintering process of boron carbide. B4C/Al2O3 composite ceramic materials were prepared using hot press-reaction sintering(RHP) and spark plasma-reaction sintering(RSPS) separately. And the density, microstructure, phase composition, mechanical properties and bullet-proof capability of as-prepared samples was studied.A thermodynamic analysis of the Al-B2O3-C reaction system was firstly conducted. The isotherm temperature at different initial temperatures was calculated. The possible phases under equilibrium were analyzed on theoretic. The formation mechanism of B4 C and Al2O3 during the combustion synthesis reaction between Al, B2O3 and C was introduced by differential thermal analysis and X-ray diffraction spectra.Dense B4C/Al2O3 composite ceramics with the matrix B4 C of 55 wt.%~80wt.% were obtained using RHP and RSPS method. The effects of composition and sintering process on the densification process were systematically investigated. The results showed that when the pressure was 35 MPa, 1750 ℃ /30 min and 1650 ℃ /3min was the best condition, respectively. For both sintering methods, higher sintering temperature and longer dwelling time lead to a decrease in the sample density. When the B4 C content was 55 wt.%, the relative density of samples by both sintering methods reached the maximum value, got 98.9%T.D. and 99.4%T.D., respectively. Mechanical properties of as-prepared B4C/Al2O3 composite ceramics were tested. The Rockwell hardness(HRA) was as high as 95 when the B4 C content was from 65 wt.% to 70 wt.%. The bending strength was 450 MPa as the B4 C content was 65 wt.%. The fracture toughness decreased with the increasing of matrix B4 C. Compared to B4 C ceramic, the fracture toughness of B4C/Al2O3 composite ceramic increased from 2.1 MPa·m1/2 to 5.2 MPa·m1/2 and increased 147.6%. Increase of the relative density and existence of the second phase(Al2O3) led to the improvements of mechanical properties.In this paper, theoretical analysis and experiment was used to research the influence of confinement on the mechanical property of ceramic. Results showed that it was feasible and effective to enhance the ability in resisting the propagation of crack by applying confinement to ceramic. After the application of confinement on the side direction, the fracture toughness of B4C/Al2O3 increased from 5.2 MPa·m1/2 to 6.5 MPa·m1/2. Ballistic experiments of ceramics with or without confinement were conducted. Results showed that B4C/Al2O3 composite ceramics this dissertation developed could effectively resist a 12.7 mm bullet and the ballistic efficiency factor was higher than AZ ceramic or B4 C ceramic. Confinement proved to be beneficial to the bullet-proof capability of ceramics because that on the one hand, mechanical properties of ceramic target board; on the other hand, the prevention of avalanche aggravated abrasion and consumed kinetic energy of penetrating bullet. |
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