First-Principles Prediction of Interstitial Carbon, Nitrogen, and Oxygen Effects on the Helium Behavior in Nickel

The effects of interstitial carbon, nitrogen, and oxygen (C/N/O) on the helium behavior in nickel are studied by using first-principles calculations. The interstitial C/N/O changes the occupying priority of helium to the first nearest neighbor Oct-site, which is related to local strain effect and chemical bonding between helium and its adjacent atoms. Both binding energy calculation and diffusion property analysis confirm that the interstitial C/N/O can trap helium in nickel. Moreover, with lower binding energy and larger trapping radii to helium, the interstitial oxygen has significant effect on helium trapping compared with that of nitrogen and carbon. With more helium aggregating at vacancy, the C/N/O would also trap smaller helium clusters and repel larger ones, indicating that the interstitial C/N/O could disperse helium bubbles and further inhibit their growth in nickel. This work helps to understand the helium embrittlement resistant mechanisms of the initial nucleation sites for second phase nanoparticles in nickel-based alloys.