Effect of Ni and Mn on the Interaction of an Edge Dislocation with Cu-rich Precipitates in Bcc Fe

Abstract

The interactions of a 1/2 <111> {110} edge dislocation with nano-sized Cu, Cu-Ni and Cu-Mn precipitates have been investigated by using of molecular dynamics method. It is found that the increase of precipitates size enhances their obstacle strength, while, the rise of temperature causes the reducing of obstacle strength. The results prove that Cu-Mn precipitates will have maximum resistance for dislocation gliding, followed by Cu-Ni and Cu precipitates. It is originated from Mn atoms in Cu-rich precipitate that exhibit attractive to dislocation segment. And Mn atoms can improve the fraction of transformed atoms from bcc structure to 9R structure for Cu-Mn precipitates with a diameter of 4 nm. These will lead to the increase of obstacle strength of Cu-Mn precipitates. For 4 nm Cu-Ni precipitate, the critical resolved shear stress is much bigger than that of 4 nm Cu precipitate, due to Ni atoms promoting the phase transition from bcc to 9R structure. Moreover, the fraction of transformed atoms is inversely proportional to temperature. Eventually, these features are confirmed that the appearance of Ni or Mn atoms enhances the obstacle strength of Cu precipitates for dislocation gliding in bcc Fe matrix, especially for Mn atoms.

Appendix

Two methods of creating Cu-rich precipitates are carried out in the present paper. The first one is developed by Osetsky and Bacon [30]. It introduces the Cu precipitate directly in modes. Cu-Mn and Cu-Ni precipitates are built by randomly replacing 40% Cu atoms in Cu precipitate by Mn or Ni atoms. The second method is to create precipitates according to experiment results. The Cu precipitates detected by Atom probe tomography in ref.8, contains some amount of Fe and Cu, as well as a little of Mn and Ni atoms. We first attain the contents of Fe, Cu, Mn and Ni elements in Cu-rich precipitates at different distances from the precipitate core to the interface. The precipitates are divided into as many isometric layers as possible, and with each layer filled using corresponding contents according to the distribution of different elements in Cu precipitates from the core to the interface. The precipitates will be introduced into the calculation models to relax adequately. The precipitates after relaxation are stable enough and interface effect between different layers in precipitates can be ignored. The corresponding pure Cu precipitate is created by substitution of the Mn and Ni atoms for Cu atoms in order to study the influence of Mn and Ni atoms on the obstacle strength of Cu-rich precipitates.

Figure A1 presents the stress-strain curves for interaction of dislocation with 4 nm Cu, Cu-Mn and Cu-Ni precipitates created by the first method. It can be seen that the Mn or Ni atoms enhance the critical resolved shear stresses of Cu-rich precipitates.

Fig. A1.

Stress–strain curves for 4 nm precipitates created by the first method at 100K

Figure A2 shows the stress-strain curves for interaction of dislocation with 4 nm pure Cu precipitate and Cu-rich precipitate containing Fe, Mn and Ni atoms built by the second method. The critical resolved shear stress for Cu-rich precipitate built by experimental results is more than 450 MPa, which is much bigger than that of pure Cu precipitate (~260 MPa). More strain (about 3%) should be applied before the dislocation departure from the Cu-rich precipitate. It reveals that the Mn and Ni atoms can improve the obstacle strength of the Cu-rich precipitate built by experimental results. It agrees with the conclusion obtained in the Fig. A1 and the dependence of stress-strain curves on strain is similar in the Figs. A1 and A2. Therefore, the first method of creating Cu-rich precipitates can be applied to qualitatively study the separate influence of Mn and Ni on the obstacle strength of Cu-rich precipitate.

Fig. A2.

Stress–strain curves for 4 nm precipitates created by the second methods at 100K