Effects of alloying elements on vacancies and vacancy-hydrogen clusters at coherent twin boundaries in nickel alloys.

The interactions between several typical alloying elements (i.e., Al, Cr, Mo, Nb and Ti) and hydrogen at coherent twin boundaries (CTB) in Ni alloys were systematically studied through first-principles calculations. It was found that solute atoms generally prefer to segregate at CTBs, with the segregation tendency prescribed by the size mismatch between the solute and host Ni atom. Moreover, there exist attractive interaction between certain solute atoms, potentially promoting solute co-segregation at CTBs. Though the solute presence does not favor hydrogen accumulation, it can considerably reduce the formation energies of vacancies and vacancy-hydrogen clusters at CTBs, which, if augmented by large-scale plastic deformation, may facilitate nanovoid nucleation to promote eventual crack initiation at CTBs. The present study demonstrated the critical role of alloying in hydrogen-induced crack initiation at CTBs, providing a new perspective towards understanding HE in Ni alloys. [ABSTRACT FROM AUTHOR]