ELSEVIER Journal of Nuclear Materials 212-215 (1994) 143-147 The threshold energy for defect production in Sic: a molecular dynamics study * J. Wong, T. Diaz de la Rubia, M.W. Guinan, M. Tobin Chemistry and Materials Science Department, Lawrence Livermore National Laboratory, L-248, Livermore, CA 94550, USA J.M. Perlado, A.S. Perez, J. Sanz Instituto de Fusion Nuclear, Universidad Politecnica de Madrid, Jose Gutierrez Abascal2, E-28006 Madrid, Spain zyxwvutsrqponmlk Abstract We discuss the results of molecular dynamics computer simulation studies of the threshold energy for defect production in P-Sic. The simulations are performed with the Tersoff potential for Sic which provides accurate values of many of its defect properties. In addition, we show that it properly describes the melting behavior of Sic. Simulations were carried out for Si and C recoils in three-dimensional cubic computational cells with periodic boundary conditions and up to 4096 atoms. The results show anisotropy in the threshold for Si and C recoils as well as for the recoil direction. The lowest threshold is 25 eV for C recoils along [ill] and the highest is 85 eV for Si recoils along [llO]. Details of the defect configurations obtained will be discussed. 1. Introduction In the last few years, Sic has been proposed as a structural component for the first wall of fusion reac- tors [l]. The most recent magnetic [2] and inertial [3] fusion reactor studies all incorporate it in their designs, either in the form of monolithic P-Sic or as SiC/SiC ceramic-matrix composites. A critical property for the increasing interest in Sic-based materials for fusion reactors is their low activation under neutron irradia- tion [4]. Low activation materials must conform to severe standards regarding their behavior under neu- tron irradiation. In particular, waste management, acci- dent safety, and maintenance considerations are most important. Sic provides a most encouraging solution, showing a significant reduction in the end-of-life ra- dioactive inventory [4]. Also, their high temperature resistance, low density and coefficient of expansion, * This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Lab- oratory under contract W-7405-Eng-48. together with a good thermal conductivity and corro- sion behavior, make these materials an excellent prospect for future fusion reactors [5]. Despite the promise of Sic-based materials as low activation components in fusion reactors, little is known about their response to high energy neutron irradia- tion. Recent work [6-81 has begun to assess the radia- tion damage-induced property changes in these materi- als. Of concern is the lattice swelling that takes place between 60 and 1000°C [9]. This results from volume changes arising from the introduction of defects and chemical disorder. Above lOOO”C, Sic exhibits void swelling [9,10], similar to metals but at a considerable lower peak rate of AV/V = 0.2%/ dpa. Also important for reactor considerations is the observed differential amorphization rate and modulus change of the matrix and the fiber in the composites [ll]. In inertial fusion reactors, sub-ps fluence bursts of = 1013 neutrons/cm2 are expected to reach the first wall as frequently as every 0.1 s, after being moderated by blanket materials [12]. Therefore, detailed knowl- edge of the primary state of damage and the diffusion properties of the point and extended defects present is 0022-3115/94/$07.00 8 1994 Elsevier Science B.V. All rights reserved SSDI 0022-3115(94)00125-S