A molecular dynamics study of temperature effects on defect production by displacement cascades in alpha-iron

Assessment of the hardening and embrittlement of pressure vessel steels and welds as a function of neutron dose uses trend curves derived from surveillance specimens. For some materials in the UK typical of those used in older plant, these curves incorporate an empirical factor to describe the temperature-dependence of matrix hardening. In the present work, molecular dynamics (MD) simulations have been used to obtain detailed information on defect number and arrangement produced in the primary cascade state of radiation damage as functions of irradiation temperature, T-irr, in alpha-iron. To allow for heat dissipation during the thermal spike phase, the continuum treatment of heat conduction was used to adjust the temperature of the boundary atoms in MD throughout the cascade process. The continuum parameters were calibrated to match those of the atomic structure, This new hybrid model allows for the variability in form between one cascade and another and has been applied to defect generation by cascades of either 2 or 5 keV at 100 K, 400 K, 600 K and 900 K. The effect of T-irr on the production of Frenkel pairs is small but statistically significant: the total number decreases by about 20-30% as T-irr increases from 100 K to 900 K. The decrease is smaller than would be consistent with the factor in the trend curves, implying that most of the observed temperature dependence arises from postcascade processes. (C) 1997 Elsevier Science B.V.