Phase evolution in the synthesis of WC-Co-Cr3C2-VC nanocomposite powders from precursors

WC-Co-Cr3C2-VC nanocomposite powders were prepared by a new precursor method, in which the amorphous oxides-C mixtures were first produced from salt solution containing tungsten, cobalt, vanadium, chromium and carbon elements by air drying and subsequent calcining at 350 degrees C for 1 h, and secondly reduced and carbonized at high temperature. Phase evolution of the reaction products was investigated systemically. The results show that the amorphous oxides-C mixtures contribute to reduction of synthesis temperature. The phase evolution of tungsten oxides follows mainly WO3 -> WO2.9 -> WO2.72 -> WO2 -> W -> WC. During the whole process of powder synthesis, Co element reacts easily with W and C elements to form eta phases (such as Co3W3C, Co6W6C and Co3W9C4). Synthesis time can promote the formation of WC phase powders, but the elimination of eta phases strongly depends on synthesis temperature. At 1100 degrees C for 2 h, the pure-phased WC-Co-Cr3C2-VC nanocomposite powders with granular particle of similar to 100-200 nm were obtained. The significant grain growth occurs especially at 1300-1400 degrees C. (C) 2013 Elsevier Ltd. All rights reserved.