The reaction bonding approach involves generally the infiltration of a compacted mixture of boron carbide and free carbon by liquid silicon. The reaction of molten silicon with boron carbide and free carbon particles leads to the formation of silicon carbide and the final fully dense composite consists of initial B₄C grains, newly formed B₁₂(B,C,Si)₃, SiC and residual Si. In the present communication, we describe a different approach for the fabrication of reaction bonded boron carbide. According to this approach, a preform, consisting of a mixture of multimodal boron carbide powders with various average particle sizes, is infiltrated with molten silicon. The preform, prior infiltration has a relatively high green density (75-80%), and the amount of the residual silicon in the final product is significantly lowered as compared to that obtained by the conventional approach. The SiC phase particles have a plate-like shape in the reaction bonded boron carbide prepared from carbon-free performs, in contrast to most SiC particles, which display a polygonal shape in the composite prepared by the conventional approach.. The reaction bonded boron carbide has a rim-core structure, which is formed in the course of a dissolution precipitation process. In samples fabricated from multi modal powder mixtures, most fine initial boron carbide particles have transformed into the new ternary B₁₂(B,C,Si)₃ phase, while the  coarse particles are surrounded by the rim layer.  A model of stoichiometric saturation, which takes into account the non-equilibrium conditions between solid and liquid solutions, was used in order to explain the microstructural evolution in the reaction bonded composites. The isothermal section at 1500⁰C of the ternary B-C-Si phase diagram, calculated using the Thermocalc software, was used for predicting the chemical reactions and the equilibrium states in the course of the interaction between boron carbide and molten silicon.

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