Effect of Alumina on the Structure and Mechanical Properties of Spark Plasma Sintered Boron Carbide

Uniform densification of relatively thick (similar to 7mm) consolidated boron carbide plates at relatively low temperatures (e.g. 1800 degrees C) and low facture toughness are two of the primary challenges for further development of boron carbide applications. This work reports that these two challenges can be overcome simultaneously by adding 5wt% alumina as a sintering aid. Nearly fully dense (97%), fine grained boron carbide (B4C) samples were produced using spark plasma sintering at 1700 degrees C and above in the B4C-5wt% Al2O3 system. The alumina and boron carbide matrix reacted to form an Al5O6BO3 (a mullite-like phase) during sintering. The Al5O6BO3 phase facilitated uniform densification via liquid phase sintering. This secondary phase is dispersed throughout the intergranular pores, providing obstacles for crack propagation and resulting in tougher boron carbide ceramics.