Study on the Effect of Segregation on the Mechanical Properties of Nanocrystalline Cu-Ni Alloys
In the classical Hall-Petch relationship,the strength of polycrystalline metals usually increases with decreasing grain size.However,the strength decreases(softening occurs)when the grain size is extremely small(usually less than 10 to 20 nm),at which point the Hall-Petch relation fails.The failure of the Hall-Petch effect suggests that the strengthening of nanocrystalline metals is not only affected by the size,but also by the stability of the grain boundary(GB).In this paper,a Cu-Ni nanocrystalline model was constructed using LAMMPS,and molecular simulations of different scenarios of grain boundary segregation of nanocrystalline Cu-Ni alloys were carried out by means of hybrid Monte Carlo/molecular dynamics(MC/MD).It is found that the presence of grain boundary segregation inhibits grain softening,the grain size effect no lon-ger dominates the mechanical properties of nanomaterials(inverse Hall-Petch effect),and solute segregation no longer has a significant strengthening effect on the nanoscale alloys.After a comprehensive analysis of grain boundary energies and dislo-cations,it can be concluded that the ideal maximum strength model is obtained by inhibiting solid solution formation and promoting grain boundary polarization while optimizing the concentration of solute atoms.The strongest mechanical proper-ties of the material are obtained when the uniform degree of segregation of the nanograin metal is about 0.9.The MD simula-tions provide the first comprehensive and in-depth study of polarization from the perspective of dislocation binding GB en-ergy.
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