Effect of heat-treatment at different temperatures on the phase and morphology of the surface of W-coated C/C composites

W-coated carbon/carbon composites have been considered as an attractive plasma facing material for ITER. W coatings were prepared on carbon/carbon substrates by double glow plasma. W-coated carbon/carbon substrates were heat-treated in a vacuum furnace at 1000, 1100, 1200, 1300 and 1400 °C for 1 h. The coatings were examined by X-ray diffraction for phase identification. The microstructure was observed by scanning electron microscopy. The chemical composition was analyzed by energy dispersive X-ray spectroscopy. The Vickers hardness was measured with a microhardness tester. The results indicated that the critical temperature for generating WC was 1200 °C. When the coatings were heat-treated below 1200 °C, the diffusion of W and C played a dominant role. W grains in 1100 and 1200 °C heat-treated samples presented a diffusion-induced rearrangement around the carbon fibers or the pores on the surface of C/C substrate. The amount of W and the hardness of the heat-treated coatings were reduced as the temperature increased. However, the reaction of W and C played a dominant role above 1200 °C. The amount of WC and the hardness of the heat-treated coatings were greatly increased as the temperature increased.