Preparation of WC–W2C composites by arc plasma melting and their characterisations

Abstract

WC–W2C composites of seven different compositions (in the range of 30–50at% C) have been prepared by arc plasma melting and in situ cooling. Microstructural characterisations of the melt-cast composites done by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, field emission scanning electron microscopy and energy dispersive spectroscopy (of X-ray) identify the various phases that grow in the composites consisting of WC, W2C and unbound C (graphite and diamond/ diamond like carbon); and the grains are seen to develop three types of contrast, such as white, grey and dark, depending on degree of carbon content. While the white grains show marginal higher microhardness than the grey ones, the dark grains show the lowest microhardness. Nanoindentation technique exhibited 31–54% higher microhardness value compared to microindentation technique. Young's moduli determined by nanoindentation technique show values in the range 514–754GPa indicating reduced brittleness of the composites. Micro Raman spectra recorded on the grey and the white grains identify presence of several molecular phases: WC (major), WCO and WO (minor). Raman peaks of C due to G, 2G, D, D′, 2D, G+D, T, T+D phases are also detected in various grains. It is found that W2C phase in the composites is not Raman active (incident with 514nm Ar+ radiation). Overall effort has been made in the work to correlate carbon content with various microstructural properties and hardness.