Synthesis of tungsten sub-carbide W2C from graphite/tungsten powder mixtures by eruptive heating in a solar furnace

Synthesis of single-phase tungsten sub-carbide phase W2C was attempted in inert Ar gas atmosphere started from compacted powder mixtures of graphite (G) and tungsten (W) with controlled mole ratios between 0.35 and 0.50 under solar radiation heating for 30 min at two target temperatures T, 1600 °C and 1900 °C, followed by initial eruptive heating from the ambient temperature to the target temperature. Under most of the examined conditions excluding the G/W = 0.50 specimens at both T = 1600 °C and 1900 °C, there was discernible proportion of non-reacted metallic W co-existed with the formed W2C. For the reference test specimen possessing the G/W mole ratio exactly at 1.0, W2C phase emerged as the trace second phase co-exiting with the principal mono-carbide phase WC. Vickers microhardness Hv was measured using a load of 25 g to be 2785 ± 335 and 2645 ± 210, respectively, for the WC phase in the G/W = 1.0 specimen and for the W2C phase in the G/W = 0.50 specimen processed at T = 1900 °C. Discrete growth of nano-meter scale WC whiskers over the top surface of the specimens heated to 1900 °C was detected by scanning electron microscope inspection.