Co-precipitated Ni/Mn shell coated nano Cu-rich core structure: A phase-field study

This work is to clarify such pending issues as the formation paths, diversity patterns, segregation modes and magnetic effect of Ni/Mn shell-coated Cu-rich particles in Fe-15at. %Cu-1at. %Mn-1at. %Ni alloy by using the phase-field method. It is found that three nucleation mechanisms (classical nucleation, non-classical nucleation and instability decomposition) can coexist in early stage of precipitation, and four kinds of structural patterns of the co-precipitates will appear during the precipitation, growth and coarsening. The Cu-rich nanoparticles gradually transform from bcc-α-Cu to fcc-γ-Cu, the Ni/Mn shell maintains bcc structure and may be precipitated on the surface of bcc-α-Cu, or fcc-γ-Cu, or both surfaces in a heterogeneous nucleation mode and runs through the whole aging stage. The Ni/Mn shell inhibits the crystal structure transformation of bcc-α-Fe matrix, the internal magnetic energy and coherent elastic strain energy also inhibit phase separation and crystal structure transformation. Therefore, we can obtain the characteristic microstructure of different aging stages by adjusting the aging time, magnetic field and elastic field conditions, so as to obtain different microstructure and corresponding mechanical properties. This work is applicable to multicomponent Fe–Cu based alloys and core–shell structural materials.