Riccardi et al. /Fusion Engineering and Design 5 000)I-22 Scale Residual SiC coating Fibres Matrix Fig. 5. SEM cross section picture of SiC/SiC sample after 10 000 h of exposure to LigSiOa of 80-100 um, identified as various silicates and 6. Joining and coatings lica, was observed, The original Sic layer is full of voids and cracks across its entire thickness sic The SiC /SiC component of a fusion reactor fibres after 10 000 h are not more protected and cannot be realised directly in the finished form but are exposed to the reacting environment. In spite they have to be realised by assembling small of these observations mechanical properties do components or half finished products. In particu- not appear to be significantly varied, indicatin lar the tauRo blanket assembly require the the bulk is not damaged up to 10 000 h. At 800c joining of small and simple parts(flat and curved the composite's Youngs modulus value after panels, T and L sections, etc. ) Nevertheless limi- 10 000 h of exposure is worsened by 30.8% while tations occur in assembling complex geometry a worsening of about 26% of the flexural strength SiC/Sic elements because welding is not possible was observed. Therefore, since the SiC coating is before reaching the melting temperature of the consumed and the fibres are exposed to the gas SiC fibres, with a partial loss of their mechanical phase a rapid reduction of the mechanical proper- properties, and because diffusion bonding does ties are foreseen for longer exposure times not seem suitable since the inter diffusion of sic As far as the compatibility of Sicr/Sic with is very low even at high temperature. For these respect to Pb-17Li is concerned, only partial data reasons the availability of a reliable joining tech- are available and they concern tests performed at nique is fundamental to realise fusion reactors 800C in stagnant liquid lithium lead using 2-D structures. In general the joints shall utilise low SiC/SiC composites. Tests for high Pb-17Li ve- activation elements, should operate at high tem locity (up to 1 m/s), with relevant duration perature(800-1000oC), should have radiation sta (10 000 h)and proper H, content, aimed at evalu- bility even at high temperature and should be ating the impact of Pb-17Li penetration through chemically compatible with the coolant and the Sicrsic thickness the composite proper- breeder. Several joining techniques are under de- ties, are still to be performed velopment. They include: assembling by sewing atB. Riccardi et al. / Fusion Engineering and Design 51–52 (2000) 11–22 19 Fig. 5. SEM cross section picture of SiC/SiC sample after 10 000 h of exposure to Li4SiO4. of 80–100 mm, identified as various silicates and silica, was observed,. The original SiC layer is full of voids and cracks across its entire thickness. SiC fibres after 10 000 h are not more protected and are exposed to the reacting environment. In spite of these observations mechanical properties do not appear to be significantly varied, indicating the bulk is not damaged up to 10 000 h. At 800°C the composite’s Young’s modulus value after 10 000 h of exposure is worsened by 30.8% while a worsening of about 26% of the flexural strength was observed. Therefore, since the SiC coating is consumed and the fibres are exposed to the gas phase a rapid reduction of the mechanical proper￾ties are foreseen for longer exposure times. As far as the compatibility of SiCf /SiC with respect to Pb–17Li is concerned, only partial data are available and they concern tests performed at 800°C in stagnant liquid lithium lead using 2-D SiCf /SiC composites. Tests for high Pb–17Li ve￾locity (up to 1 m/s), with relevant duration (10 000 h) and proper H2 content, aimed at evalu￾ating the impact of Pb–17Li penetration through the SiCf /SiC thickness on the composite proper￾ties, are still to be performed. 6. Joining and coatings The SiCf /SiC component of a fusion reactor cannot be realised directly in the finished form but they have to be realised by assembling small components or half finished products. In particu￾lar the TAURO blanket assembly require the joining of small and simple parts (flat and curved panels, T and L sections, etc.). Nevertheless limi￾tations occur in assembling complex geometry SiCf /SiC elements because welding is not possible before reaching the melting temperature of the SiC fibres, with a partial loss of their mechanical properties, and because diffusion bonding does not seem suitable since the inter diffusion of SiC is very low even at high temperature. For these reasons the availability of a reliable joining tech￾nique is fundamental to realise fusion reactors structures. In general the joints shall utilise low activation elements, should operate at high tem￾perature (800–1000°C), should have radiation sta￾bility even at high temperature and should be chemically compatible with the coolant and breeder. Several joining techniques are under de￾velopment. They include: assembling by sewing at