Microstructure of Platelet-Reinforced Ceramics Prepared by the Directed Reaction of Zirconium with Boron Carbide

The microstructure of a ZrB₂-platelet-reinforced ZrC _x composite was examined using transmission electron microscopy and X-ray diffraction. The composites, which are formed by the reaction of molten Zr with B₄C, contain a small amount of residual Zr, the amount of which can be varied by altering the processing conditions. Results on two different materials are reported, one with a low Zr content, ∼2.5 vol%, and the other with a very low Zr content, ∼0.5 vol%. In the former, metallic Zr was found at triple points and as a grain boundary phase between the boride and carbide, and to a lesser degree between the boride grains. In the latter, it was only found as a ternary Zr–ZrB₂–ZrC _x eutectic at the triple points. Both materials showed a nearly random distribution of the boride and carbide constituents, though specific crystallographic relationships were found between the various constituents.