In this part, we studied tungsten carbide (WC) as a reducing agent for the oxide phase present on tungsten particles. Namely, at a high sintering temperature in contact with tungsten, the toilet consumes part of the oxygen.Based on the calculation, at least 5.8 vol % WC must be introduced into the starting mixture to completely remove the oxygen impurities in the form of CO and CO2 and to obtain pure tungsten. Surplus amount of WC will lead to the formation of a thermally stable W2C as a second phase at 1900 °C.
COBISS.SI-ID: 32476967
Here we report on the development of new composite, WC-reinforced tungsten, for the DEMO divertor. The microstructure, mechanical properties, thermal stability and thermal conductivity were analysed with the aim to select the most favourable composition. The particle reinforcement of tungsten was achieved by incorporating WC nanoparticles. W2C particles are formed at the tungsten grain boundaries during densification by carbon diffusion from the WC particles. After densification by FAST at 1900 °C, 5 min, two phases are detected in the sintered composite: cubic W and hexagonal W2C, which implies the complete transformation of the WC. The addition of at least 5 vol % of the submicron WC successfully prevented the oxidation of W, while larger amounts contributed to the beneficial formation of the desired carbide particle W2C, which inhibits tungsten grain growth during ageing at high temperatures. The composite with the addition of approximately 10 vol % WC inclusions (sample W–10WC) reflects the highest flexural strength at RT ()1200 MPa) as well as at elevated temperatures, with the onset of plastic deformation at 600 °C. Moreover, the high-temperature thermal conductivity is relatively high and remains above 100 Wm/K up to 1000 °C. Thus, the results suggest improved properties of this composite in comparison with state-of-the-art materials, and therefore the material will be subject to high-heat-flux testing.
COBISS.SI-ID: 32869927
This study discusses the formation of phases during sintering of tungsten by the FAST. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were used to evaluate the microstructure in tungsten-based materials. The results of microscopic examinations revealed the in-situ formation of tungsten oxide and a formation of tungsten carbide shell around tungsten core. Tungsten carbide-rich shell is formed due to the carbon diffusion from the graphite die used in the FAST into tungsten at high temperatures.
COBISS.SI-ID: 31225127