a b s t r a c tUsing molecular dynamics simulations, we elucidate irradiation-induced point defect evolution in fcc pure Ni, Ni 0.5 Fe 0.5 , and Ni 0.8 Cr 0.2 solid solution alloys. We find that irradiation-induced interstitials form dislocation loops that are of 1/3h1 1 1i{1 1 1}-type, consistent with our experimental results. While the loops are formed in all the three materials, the kinetics of formation is considerably slower in NiFe and NiCr than in pure Ni, indicating that defect migration barriers and extended defect formation energies could be higher in the alloys than pure Ni. As a result, while larger size clusters are formed in pure Ni, smaller and more clusters are observed in the alloys. Vacancy diffusion occurs at relatively higher temperatures than interstitials, and their clustering leads to the formation of stacking fault tetrahedra, consistent with our experiments. The results also show that the surviving Frenkel pairs are composition dependent and are largely Ni dominated.

Abstract

Irradiation-induced damage accumulation in Ni 0.8 Fe 0.2 and Ni 0.8 Cr 0.2 alloys are investigated using molecular dynamics (MD) simulations to assess possible enhanced radiation-resistance in these face-centered cubic (fcc), single-phase, concentrated solid-solution alloys, as compared with pure fcc Ni. The Ni 0.8 Cr 0.2 and Ni 0.8 Fe 0.2 alloys demonstrate higher radiation resistance compared to Ni. The total number of point defects produced in Ni 0.8 Cr 0.2 and Ni 0.8 Fe 0.2 is approximately 2.5 and 1.4 times lower than in Ni, respectively, due to efficient defect recombination in the chemically disordered alloys. Both interstitial and vacancy clusters are formed in all three materials. In Ni, large interstitial clusters are produced; whereas in Ni 0.8 Cr 0.2 , smaller interstitial clusters are produced but with a higher number. This indicates a higher mobility of interstitials in Ni compared to Ni 0.8 Cr 0.2. Moreover, Ni 0.8 Cr 0.2 shows better radiation resistance than Ni 0.8 Fe 0.2. Larger interstitial clusters and 1.7 times higher numbers of accumulated point defects are observed in Ni 0.8 Fe 0.2 , in comparison with Ni 0.8 Cr 0.2. Due to the low mobility of vacancies on the MD time scales, they are found primarily as single point defects and small clusters in all materials. While performance improvement is observed in the alloys, the difference in irradiation response between Ni 0.8 Cr 0.2 and Ni 0.8 Fe 0.2 indicates the importance of element choice to achieve the desired property.

Grain growth of nanocrystalline materials is generally thermally activated, but can also be driven by irradiation at much lower temperature. In nanocrystalline ceria and zirconia, energetic ions deposit their energy to both atomic nuclei and electrons. Our experimental results have shown that irradiation-induced grain growth is dependent on the total energy deposited, where electronic energy loss and elastic collisions between atomic nuclei both contribute to the production of disorder and grain growth. Our atomistic simulations reveal that a high density of disorder near grain boundaries leads to locally rapid grain movement. The additive effect from both electronic excitation and atomic collision cascades on grain growth demonstrated in this work opens up new possibilities for controlling grain sizes to improve functionality of nanocrystalline materials.