Mg/B4C Composites with a High Volume Fraction of Fine Ceramic Reinforcement

Abstract

The results of a study aimed at establishing an understanding of the role of particulate reinforcement on the hardness and tensile deformation of a magnesium-based matrix discontinuously-reinforced with a high volume fraction (approx. 50 vol%) of boron carbide (B4C) particulates are reported. Composites were fabricated by pressureless infiltration of porous boron carbide preforms with molten magnesium under a flowing nitrogen atmosphere. The capabilities of such a fabrication route for production of magnesium-based composites with a high volume fraction of a bimodal mixture of coarse (d 50 = 44 µm) and fine (d 50 = 0.8 µm) boron carbide particulates uniformly distributed in the matrix were also investigated. The successful initiation of spontaneous infiltration was found to be influenced by several processing parameters which were identified and investigated. Thus, the microstructure and mechanical properties of the fabricated composites were investigated in the light of the influence of the initial perform composition (boron carbide bimodal mixture composition and the wetting agents (Si and Ti powders) applied) and the infiltration parameters. The high volume fraction of particulate reinforcement content successfully achieved by pressureless infiltration was found to improve the hardness and tensile properties of the composites significantly compared to unreinforced counterparts. On the contrary, the reinforcement had a detrimental influence on ductility. Moreover, the experimental findings clearly confirmed that the influence of the reinforcing boron carbide phase on the mechanical response of Mg/B4C composites is predominantly through the volume fraction of ceramic particulate in the matrix, and much less through the average particle size of the ceramic filler applied.