Atomic-scale understanding of interfacial structure and chemistry effects on hydrogen trapping and migration in Cu-precipitation-strengthened steels

Cu-nanoparticles strengthened steels have received considerable attention due to their high strength and excellent resistance to hydrogen embrittlement, but an atomistic understanding of hydrogen-precipitate interaction mechanisms have not been clearly elucidated. In this study, we thoroughly investigate the influence of crystal lattice, interfacial structure, and solute segregation on hydrogen trapping and migration behaviors in a Fe–Cu–(Ni,Mn) system by using first-principles calculations. Our results shows that the Cu/Fe heterophase interfaces, rather than the precipitate cores, are preferable hydrogen trapping sites, and the hydrogen solution enthalpy of the interfaces follows the order of fcc-Cu/bcc-Fe < 9R-Cu/bcc-Fe < bcc-Cu/bcc-Fe. We found that the interfacial misfit and solute segregation are two important factors in determining the hydrogen trapping energetics. Specifically, large interfacial misfit can induce large fluctuations in interstitial volume, which results in large space for hydrogen trapping. Moreover, large interfacial misfit also leads to a large energy barrier and a rugged energy landscape for hydrogen migration along and across the Cu/Fe interfaces, which results in decreased hydrogen mobility at the interfaces. In addition, solute segregation of Mn and Ni at the Cu/Fe heterophase interfaces can further enhance the hydrogen trapping due to their strong chemical bonding with hydrogen atoms. Finally, we compared our calculation results with experimental observations, which shows a satisfactory agreement. These findings shed insights into the mechanism of the interfacial structure and chemistry effects on hydrogen trapping, which helps in the design of novel steels with high resistance to hydrogen embrittlement by interfacial engineering.