Effects of segregated Cu on an Fe grain boundary by first-principles tensile tests.

Cu is known as one of the harmful tramp elements in recycled Fe. In the present work, the effects of Cu on Fe grain boundary (GB) embrittlement have been investigated by first-principles tensile tests. Because the Fe-Cu bonds are rather isotropic and the effects due to their difference in atomic size are negligibly small, the GB atomic structure prior to straining is little changed by Cu segregation. However, the Fe-Fe bond around the Cu atom is weakened due to charge transfer from the Fe atom to the Cu atom, and premature bond breaking occurs at the weakened Fe-Fe bond, resulting in an enhancement of GB embrittlement by Cu segregation. The s and p electrons play a vital role in the charge transfer.