Studyon The Mechanism Of Al₂O₃-matrix Composite Ceramics Fabricated By Combustion Synthesis With Centrifugation And Casting

Al2O3ceramic have a wide range of applications in the field of ceramic armor for its low cost and fine performance.The Al2O3matrix composite ceramic can be obtained to improve its anti-bullet property by adding ZrO2,B4C or TiB2to Al2O3.In this paper,the exothermal reaction between Al and Zr(NO3)4was used to heat and melt the experiment system.The Al2O3/ZrO2eutectic ceramic with high eutectic proportion could be fabricated through the process of cooling, solidification and crystallization,and the toughening mechanism of Al2O3/ZrO2eutectic ceramic was studied.In order to strengthen and toughening the material by adding tungsten and carbon fiber,the interface bonding between tungsten,graphite and Al2O3/ZrO2eutectic was studied.For improving the material’s anti-bullet property,the high-temperature reaction mechanism of Al-Zr(NO3)4-B4C(or B4C-TiB2) and Al-Al(NO3)3-B4C(or B4C-TiB2) was studied.The adiabatic temperature and pressure of all the reaction system were calculated and measured.In this paper,the exothermal reactions of Al-Zr(NO3)4and Al-Al(NO3)3were used to heat the experiment system and the theoretical adiabatic temperature of the system could easily reach3000-4000K.Under the condition of ultra-temperature,the ceramic with fine microstructure could be obtained via rapid cooling and solidification. The pressure of the system was lower than7MPa,which was corresponding to combustion synthesis under low pressure.Al2O3/ZrO2eutectic ceramics with nearly100%eutectic were fabricated by combustion synthesis under low pressure and its hardness,bending strength and fracture toughness were16.39lGPa,1060MPa and11.2MPa.m1/2respectively.The toughening mechanism of Al2O3/ZrO2eutectic ceramic was studied by XRD and SEM analysis.The toughness could be strengthen through pull-out and fracture of rod-like ZrO2phase,crack deflection,residual compressive stress and the t-m phase change of t-ZrO2.The interface bonding between tungsten,graphite and Al2O3/ZrO2eutectic was studied by SEM analysis.The thin interface reaction layer,which existed between tungsten and Al2O3/ZrO2mainly included tungsten oxide,alumina,zirconia and intermetallic compound formed by W,Al and Zr.Through rapid cooling,the interface reaction layer’s thickness was less than5μm and the interface bonded well.Some gas would be released from the reaction between graphite and c eutectic so that the interface combined badly.the high-temperature reaction mechanism of Al-Zr(NO3)4-B4C(or B4C-TiB2) and Al-Al(NO3)3-B4C(or B4C-TiB2) was studied.B4C would be transformed into B13C2in the exothermal system of Al-Zr(NO3)4and AlB12C2in the exothermal system of Al-Al(NO3)3.The TiB2maintained its chemical inertia and didn’t participate in the reaction.For further studying the reaction degree,the B4C and B4C-TiB2slice were added in the system of Al2O3/ZrO2eutectic. The reaction layer’s thickness was less than100μm and the reaction degree of B4C and B4C-TiB2slice would increase with the temperature increasing,but the interface bonded better.