B. Riccardi et al./Fusion Engineering and Design 51-52(2000)11-22 stress with the absence of interlaminar delamina en and the increase of the matrix crystallinity tion during manufacturing and use, and lower and properties. Recently, the use of an hybrid dispersion of the shear strength process combining CVI and PIp processes al CERASEP N3-1 features can be improved by lowed the fabrication of composites with relevant high purity SiC fibres virtually stoichiomet thicknesses(6 and 10 mm) with an intermediate ric and oxygen freeand with thermal conductiv- matrix structure [13]. Flat panels were produced ity intrinsically higher than that of the with different duration of CVI process and num- NICALONTM CG. Benefits with respect neutron ber of PIP cycles. The maximum density for 10 irradiation induced change in the fibre properties mm thick panels was reached at 60 h of CvI and are expected. Other positive aspects related to the seven PIP cycles( 2.05 g cm-2) use of such fibres are: an increasing in the maxi mum operating temperature from 1100 to 1300oC and improvements in mechanical properties 4. radiation In parallel with Sic, SiC composite manufac turing by the CVI technique, alternative matrix Neutron and particle irradiation induces dis- processing routes are going to be investigated, in placement damage and helium production in SiC particular polymer infiltration and pyrolisis(Pip) based materials, In order to assess the effect of [12]. This technology is less expensive than CVI, irradiation damage and He production on the can be carried out at lower temperature and al- mechanical properties of Sic /SiC structural com- lows the manufacturing of more complex shapes posites a testing campaign was carried out at the ENEA has extensively used preceramic polymers Institute of Advanced Materials/Joint Research with SiC nanopowders. This composites exhibited Centre, Ispra-Italy up to 1998. In particular the interesting mechanical properties in particular material tested was produced by the SEP Division high strain to failure and toughness. As all com- of SNECMA using a 2-D woven laminate of posites produced by PIP, the material exhibits NICALONTM fibres and a CVI infiltration of lower thermal conductivity, poor crystallinity and B-SiC matrix. The neutron irradiation of SiC/ SiC high residual oxygen content. The availability specimens was carried out at the high flux reactor more advanced fibres allowing higher pyrolysis (HFR), Petten-NL up to accumulated damage temperature will permit the reduction of free oxy- doses of 1. 29, 2.69 and 5.23 dpa at 750C irradia- Table I SEP SiCSiC composites main properties roperty Temperature CERASEP N2-1 CERASEP N3. (2-D) 2.5 2.4 10±2 Fibre content (%) Tensile strength(in plane)(MPa) ile strain (in plane)(%) ung module Trans-laminar shear strength Inter-laminar shear strength(MPa) 00-0000000 0.8±0.25 200 200±20 200 MPa 200+20GPa Thermal conductivity (in plane)(Wm-K-) 15 Thermal conductivity(trough the thickness)(W m-K 3±2 Thermal conductivity(trough the thickness)(W m-K Thermal conductivity(trough the thickness)(W m-K Thermal expansion coefficient (in plane)(K-) 4.0×10=6 4.0×10 Thermal expansion coefficient(trough the thickness)(K-) 20 2.5×10B. Riccardi et al. / Fusion Engineering and Design 51–52 (2000) 11–22 15 stress with the absence of interlaminar delamina￾tion during manufacturing and use, and lower dispersion of the shear strength. CERASEP® N3-1 features can be improved by using high purity SiC fibres virtually stoichiomet￾ric and ‘oxygen free’ and with thermal conductiv￾ity intrinsically higher than that of the NICALON™ CG. Benefits with respect neutron irradiation induced change in the fibre properties are expected. Other positive aspects related to the use of such fibres are: an increasing in the maxi￾mum operating temperature from 1100 to 1300°C and improvements in mechanical properties. In parallel with SiCf /SiC composite manufac￾turing by the CVI technique, alternative matrix processing routes are going to be investigated, in particular polymer infiltration and pyrolisis (PIP) [12]. This technology is less expensive than CVI, can be carried out at lower temperature and al￾lows the manufacturing of more complex shapes. ENEA has extensively used preceramic polymers with SiC nanopowders. This composites exhibited interesting mechanical properties in particular high strain to failure and toughness. As all com￾posites produced by PIP, the material exhibits lower thermal conductivity, poor crystallinity and high residual oxygen content. The availability of more advanced fibres allowing higher pyrolysis temperature will permit the reduction of free oxy￾gen and the increase of the matrix crystallinity and properties. Recently, the use of an hybrid process combining CVI and PIP processes al￾lowed the fabrication of composites with relevant thicknesses (6 and 10 mm) with an intermediate matrix structure [13]. Flat panels were produced with different duration of CVI process and num￾ber of PIP cycles. The maximum density for 10 mm thick panels was reached at 60 h of CVI and seven PIP cycles ( 2.05 g cm−2 ). 4. Irradiation Neutron and particle irradiation induces dis￾placement damage and helium production in SiC￾based materials. In order to assess the effect of irradiation damage and He production on the mechanical properties of SiCf /SiC structural com￾posites a testing campaign was carried out at the Institute of Advanced Materials/Joint Research Centre, Ispra-Italy up to 1998. In particular the material tested was produced by the SEP Division of SNECMA using a 2-D woven laminate of NICALON™ fibres and a CVI infiltration of b-SiC matrix. The neutron irradiation of SiCf /SiC specimens was carried out at the high flux reactor (HFR), Petten-NL up to accumulated damage doses of 1.29, 2.69 and 5.23 dpa at 750°C irradia￾Table 1 SEP SiCf /SiC composites main properties Property Temperature CERASEP CERASEP ® N3-1 ® N2-1 (°C) (3-D) (2-D) Density (g/cm 20 2.5 3 ) \2.4 Porosity (%) 20 10 1092 Fibre content (%) – 40 40 Tensile strength (in plane) (MPa) 300 20 285 920 Tensile strain (in plane) (%) 0.75 0.8 20 90.25 Young modulus (in plane) (GPa) 200 20 200920 Trans-laminar shear strength 20 200 MPa 200920 GPa Inter-laminar shear strength (MPa) 44 20 – Thermal conductivity (in plane) (W m 1000 15 15 −1 K−1 ) Thermal conductivity (trough the thickness) (W m 20 9 1392 −1 K−1 ) Thermal conductivity (trough the thickness) (W m 5.8 7.6 −1 K−1 ) 800 Thermal conductivity (trough the thickness) (W m 1000 5.7 7.5 −1 K−1 ) 20 4.0×10−6 Thermal expansion coefficient (in plane) (K−1 ) 4.0×10−6 2.5×10 – −6 Thermal expansion coefficient (trough the thickness) (K−1 ) 20