Studies Of The SiC/B4C Composite Fabricated By Method Based On Reaction Sintered SiC

Due to its low density, high hardness, high melting point and high chemical stability, etc., boron carbide (B4C) has found applications in various areas, such as military industries, mechanics, chemical engineering, aeronautics, and energy. Currently, nearly all B4C based ceramics are produced by hot-pressing method, with low fracture toughness and high fabrication costs hampering its applications. Introduction of the second phase (TiB2, ZrB2, SiC, etc.) can improve the fracture toughness of B4C. Nevertheless, some problems have to be solved in the production, such as deformation, cracks and high fabrication costs. Therefore, there is a demand in developing a simple and low-temperature-sintering approach to fabricating B4C composite without deformation in shapes and compromise in properties. This work is thus believed to be of high importance in exploiting the potential in applications. Specifically, this work, based on reaction sintering, is to fabricate dense SiC/B4C composite and to study the influence of carbon content on the phase compositions, microstructure, density and mechanical properties.The main results are:(1) SiC/B4C composite has been successfully synthesized by infiltration of molten silicon at1550℃under vacuum into a porous compact composed of boron carbide and carbon powders.(2) Phase composition of the composite are:B4C, SiC, Si, B13C2and B12.97Si0.3C2. During the infiltration process, silicon reacted with carbon and formed silicon carbide; some fine B4C particles reacts with molten silicon to form SiC and B13C2phases with enriched boron and B12.97Si0.3C2as well.(3) The microstructure analysis shows that:the SiC phases and B4C phases distributes in the composite uniformly, while free Si fills in the continuous gaps between B4C and SiC phases. The numbers and sizes of some sporadic abnormally grown B4C grains increase with the increase in C contents.(4)The mechanical properties of SiC/B4C composites improve initially and then deteriorate with the increase in C contents. When the carbon content equals to10%, overall mechanical properties of the composite reach the maxima. The Viker-hardness, bending strength and fracture toughness were24.39GPa,361.31MPa and4.41MPa-m1/2, respectively. At the same time, the open porosity, volumetric density and relative density of the obtained SiC/B4C ceramic composite are0.19%、2.58g/cm3,99.11%, respectively.