Interest in ferritic and ferritic-martensitic steels has stimulated the development of Fe-Cr potentials such as those discussed by Malerba and coworkers.129 These potentials have been applied to investigate the influence of Cr on displacement cascades13 , and on point defect diffusion.1 The MD cascade study by Malerba and coworkers130 involved cascade energies from 0.5 to 15keV at 300 K. In contrast to the Fe-C and Fe-Cu results discussed above, a slight increase in stable defect formation was observed in Fe-10%Cr relative to pure Fe. The asymptotic value of the defect survival ratio (relative to the NRT) at the highest energies was 0.28 for Fe and 0.31 for Fe-10%Cr. In a later study by the same

authors, which involved a larger number of simula­tions and energies up to 40 keV, they also concluded that the presence of 10%Cr did not lead to a change in the collisional phase of the cascade but rather reduced the amount of recombination during the cooling phase.1 Additional detailed studies per­

formed with more recent Fe-Cr potentials essentially confirmed the absence of any significant effect of Cr on primary damage in Fe-Cr alloys as compared to pure Fe.136-138

The lack of a Cr effect on the collisional or ballistic phase of the cascade may be expected because, like Cu, the mass of Cr is similar to Fe. The reduced recombination appears to be related to the formation of highly stable mixed Fe-Cr dumb­bell interstitials. About 60% of interstitial dumbbells contain a Cr atom, which is substantially higher than the overall Cr concentration of 10%. In spite of the strong mixed dumbbell formation, the fraction of point defects in clusters did not seem to be signifi­cantly different than in pure Fe. However, if the stability and mobility of the mixed dumbbells and clusters containing them proves to be appreciably different than pure iron dumbbells,1 2 there could be an influence on damage accumulation at longer times. Experimental results that are consistent with this hypothesis135 are mentioned in Terentyev and

coworkers.138