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

Abstract WC–Co–Cr 3 C 2 –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 °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 WO 3 → WO 2.9 → WO 2.72 → WO 2 → W → WC. During the whole process of powder synthesis, Co element reacts easily with W and C elements to form η phases (such as Co 3 W 3 C, Co 6 W 6 C and Co 3 W 9 C 4 ). Synthesis time can promote the formation of WC phase powders, but the elimination of η phases strongly depends on synthesis temperature. At 1100 °C for 2 h, the pure-phased WC–Co–Cr 3 C 2 –VC nanocomposite powders with granular particle of ~ 100–200 nm were obtained. The significant grain growth occurs especially at 1300–1400 °C.