Atomic-scale computer simulation study of the interaction of Cu-rich precipitates with irradiation-produced defects in α-Fe

Abstract

Copper-rich precipitates can nucleate and grow in ferritic steels containing small amounts of copper in solution and this affects mechanical properties. Growth kinetics, composition and structure of precipitates under irradiation are different from those under thermal ageing, and also vary with type of radiation. This implies that the interaction between radiation defects, i.e. vacancies, self-interstitial atoms (SIAs) and their clusters, and precipitates is influential. It is studied here by atomic-scale computer simulation. The results are compared with those of elasticity theory based on the size misfit of precipitates and defects, and the modulus difference between bcc iron and bcc copper. It is found that SIA defects are repelled by precipitates at large distance but, like vacancies, attracted at small distance. Copper precipitates in iron can, therefore, be sinks for both vacancy and interstitial defects and hence can act as recombination centres under irradiation conditions. A tentative explanation for the mixed Cu–Fe structure of precipitates observed in experiment and the absence of precipitate growth under neutron irradiation is given. More generally, agreement between the simulations and elasticity theory suggests that the results are not artefacts of the atomic model: both vacancy and interstitial defects in metals may bind to precipitates with weaker cohesion than the matrix.

Acknowledgments

ACA would like to thank the University of Liverpool for providing a studentship grant. This work was performed under a research grant from the UK Engineering and Physical Sciences Research Council and partly supported by the Division of Materials Sciences and Engineering and the Office of Fusion Energy Sciences, US Department of Energy, under contract DE-AC05-00OR22725 with UT–Battelle, LLC. We thank Dr Ian C. Smith of the CSD Department for the provision of computing resources of the University's experimental Condor service.