Study on the preparation mechanism of novel WC-Cr2(C, N)-Co nanocomposites

Abstract

In this work, the WC-Cr2(C, N)-Co nanocomposites were synthesized by using the one-pot carbothermal reduction nitridation hydrothermal precursor method. The preparation mechanisms, including phase and morphology evolutions, were investigated by differential thermal analysis (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermodynamic analysis. The results showed that phase evolution, with temperature increasing, follows the sequences of (amorphous phase, WO2.72) → (CoWO4, WO2.72, WO2, CrWO3) → (WO2, CoWO4, Co6W6C, CrWO3) → (W2C, Co3W3C, WC) → (WC, W2C, Co3W3C) → (WC, Co, Co3W3C trace amount). Through comparing different heat treatment conditions, the powder particle size was more easily affected by temperature than holding time. The higher temperatures or longer time holding resulted in the aggregation of powder particles. Finally, WC-Cr2(C, N)-Co nanopowders with about 60 nm were obtained at 1050 °C for 1 h under the N2 flow of 1 L/min with the oxygen content of 0.22 wt% and the free carbon content of 0.19 wt%. The TEM elements mapping revealed that Cr distributes uniformly with WC grains, Co and WC grains are combined well. The surface of WC-Cr2(C, N)-Co determined by XPS is mainly composed of W, Co, Cr, C, N, and O. The spark plasma sintering (SPS) sintered WC-Cr2(C, N)-Co composite shows a nanocrystalline microstructure with the average grain size ∼170 nm, and the excellent comprehensive mechanical properties with the Vickers hardness 1730 Kg·mm−2 and fracture toughness 11.5 MPa·m1/2, respectively.