Interaction of a screw dislocation with Cu-precipitates, nanovoids and Cu–vacancy clusters in BCC iron

In a previous work we studied the interaction of a ½h111i{110} edge dislocation with Cu-rich precipitates containing also vacancies and Ni, thereby mimicking precipitates known to form in RPV steels [1]. Here, we extend the study and consider the interaction of the Cu-rich precipitates with ½h111i screw dislocations, known to govern the slip in BCC metals and alloys below room temperature. The results show that three different mechanisms take place upon interaction of a screw dislocation with pure Cu precipitates, nanovoids and Cu–vacancy clusters. Pure Cu precipitates are always sheared, while in the reaction with nanovoids local climb, especially at high temperature, is also observed. The interaction mechanisms studied at various temperatures reveal that the penetration of the screw dislocation into Cu–vacancy clusters leads to absorption of the majority of the vacancies on the dislocation line, with the consequent formation of a helical turn. The removal of the helical turn, even a very small one, from the dislocation line requires as high stress as for the passage through a row of nanovoids of comparable size.