Low-activation W–Si–C composites for fusion application

Abstract

W–Si–C composites were fabricated by active filler controlled pyrolysis of W powder (high tungsten content) and W–SiC powder mixtures (low tungsten content), infiltrated by a preceramic polymer and heat treated at temperatures from 1600 to 2000°C. Material with high volume fraction of W in initial powder–polymer mixture, formed a composite material composed of W, W2C and W5Si3 with closed porosity in a single polymer infiltration and pyrolysis (PIP) cycle. After heat treatment at 1700°C the material exhibited flexural strength above 350MPa, hardness of 7.8GPa and indentation modulus of 250GPa. Room temperature thermal conductivity of the composite was rather low, 23Wm−1K−1, however, thermal conductivity increased with increasing temperature achieving 35Wm−1K−1 at 1000°C. The effect of W as active filler in W–SiC powder mixtures with low volume fraction of tungsten was negligible. Therefore, six polymer infiltration and pyrolysis cycles were used to achieve significant densification with 15% porosity. The material fabricated at 1800°C was composed of SiC, WC and WSi2 and exhibited flexural strength of ∼400MPa and room temperature thermal conductivity of 100Wm−1K−1, which decreased to 32Wm−1K−1 at 1000°C.