MICROSTRUCTURE OF PLATELET-REINFORCED CERAMICS PREPARED BY THE DIRECTED REACTION OF ZIRCONIUM WITH BORON-CARBIDE

The microstructure of a ZrB2-platelet-reinforced ZrCx 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, approximately 2.5 vol%, and the other with a very low Zr content, approximately 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-ZrCx 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.