Mechanically induced solid state carburization for fabrication of nanocrystalline ZrC refractory material powders

Nanocrystalline powders of the nearly equiatomic composition Zr(56)hC(44) have been successfully synthesized at room temperature by high-energy ball milling of elemental Zr and C powders. For the purpose of the present study, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been employed to monitor the progress of the solid state reaction at several stages of the milling time. A complete single phase of fcc-ZrC was obtained after 173 ks of milling, time. No free Zr and/or C crystals could be detected at this final stags of milling. The lattice parameter of the as-milled ZrC was calculated to be 0.47082 nm. The fabricated ZrC powders posses excellent morphological characteristics, such as homogeneous shape (spherical-like morhology) With fine and smooth surface relief and uniform size (less than 0.5 mu m in diameter). These fabricated refractory material powders have line cell-like structure with nanoscale dimensions of about 5 nm in diameter. Cold and hut pressing techniques have been used to consolidate the end-product of the milled powders (259 ks) into fully dense (>99.5%) compact. In the consolidation procedure, the powders were pressed at 1573 K with a pressure of 1.0-1.5 GPa for 43 ks. This consolidation step led to a remarkable grain growth, and the compacted Zr-C sample contained grains larger than 95 nm in diameter, but maintained its nanocrystalline unique characteristics. The density and Vickers hardness of the bulk ZrC were measured as 6.56 g/cm(3) and 27 GPa, respectively. A model for the formation of nanocrystalline fully dense refractory materials is proposed, taking the ZrC binary system as a typical example. (C) 2000 Elsevier Science S.A. All rights reserved.