Paper Title
Light Absorbance and Machinability of TIB2-SIC-C Ultra-High-Temperature Ceramics

Abstract
The reaction assisted hot pressing approach [1] allows obtaining nonporous TiB2-SiC-C ultra-high-temperature ceramics at 1850°C (30MPa and 2min sintering) by the following in-situ reaction: 2TiC + B4C + xSi → 2TiB2 + xSiC + (3-x)C The exothermic reaction positive impact on the green body densification kinetics in this case surpasses that of a Spark-Plasma Sintering for the investigated TiB2-SiC-C based systems. It is shown that carbon is emerging from the precursors during the charge consolidation/reactions nucleates into submicron graphite platelets. The carbon platelets enhance the material mechanical properties. The crack tip blunting in the soft particles [2] precludes crack propagation. This leads to toughness growths from 7MPa∙m1/2 to almost 10MPa∙m1/2. Moreover, this process, combined with the Young’s modulus reduction, leads to rise of the thermal shock stability. TiB2-SiC-C ceramic is by an order of magnitude more shock resistant as comparing to pure TiB2-SiC matrix. The TiB2-SiC-C composite hardness is degrading as the soft phase content, graphite platelet concentration, increases. The produced ultra-high-temperature ceramics are shown to be machinable as the platelet content approaches and exceeds 20 vol.%. The investigation of sintered materials optical characteristics with the use of laser ellipsometer at the wavelength of 632.8 nm showed that the TiB2-SiC matrix absorbance (~65%) is higher than that of pure titanium diboride (~55% [3]). High coefficient of light absorption combined with high thermal shock and crack resistance allows to recommend the reactively sintered TiB2-SiC-C ultra-high-temperature ceramics as a perspective concentrated solar power absorbers.