Effect Of SiO₂ Additive On Shs Reaction Of The Al-TiO₂-H₃BO₃ System

According to Al-TiO₂-H3BO3 system, high performance Al₂O₃-TiB2 ceramic composite is prepared by self-propagating high-temperature synthesis in air atmosphere at room temperature. And on this basis, further improve the ceramic composite properties (strength and hardness) by adding SiO₂ additive. The phase composition, microstructure and fracture morphology of the materials are analyzed by XRD, OM and SEM. The density, hardness and bending strength properties of the Al₂O₃-TiB2 ceramic composite material are also measured. Experiment results show that, the adiabatic temperature (Tad) of Al-TiO₂-H3BO3 system is 2588 K, and decreases with increasing SiO₂ addition. With the increase of SiO₂ content, combustion wave velocity of the system decreased rapidly. The combustion wave velocity is also increased by milled reactants or taken insulation measures during the reaction. With SiO₂ addition, the phases of SiO₂ and Al6O13Si2 emerge in the ceramic composite. The addition of SiO₂ results in refined grain size of TiB2 and made each phase in the product distributions more uniform. Under the same conditions, the density, hardness and bending strength of the ceramic composite increased with the increase of SiO₂ content when the addition of SiO₂ changed from 0 to 20%. The density, hardness and bending strength of the Al₂O₃-TiB2 ceramic composite is reached peak value of 1.60 g/cm3, 1362 HV and 241 MPa respectively with the addition of 20 vol. % SiO₂. But the porosity decreased continuously with the increase of SiO₂ content. The density, hardness and bending strength of the synthetic products begun to decline with more than 20 vol. % SiO₂ added. When the SiO₂ content is constant, the density, hardness and bending strength of the composite are increased by milled reactants or taken insulation measures during the reaction. And the porosity decreased, the volume change is inhibited as well. The fracture mode of Al₂O₃-TiB2 ceramic composite is intergranular fracture mode mixed with transgranular fracture, and as intergranular fracture for the main mode. The proportion of transgranular fracture increased significantly with the increase of SiO₂ content. This shows that the brittleness of the composite is reduced and the fracture toughness is increased.