Effect of P impurity on NiAlΣ5 grain boundary from first-principles study

First-principles calculations based on the density functional theory（DFT） and ultra-soft pseudopotential are employed to study the atomic configuration and charge density of impurity P in Ni Al Σ5 grain boundary（GB）. The negative segregation energy of a P atom proves that a P atom can easily segregate in the Ni Al GB. The atomic configuration and formation energy of the P atom in the Ni Al GB demonstrate that the P atom tends to occupy an interstitial site or substitute a Al atom depending on the Ni/Al atoms ratio. The P atom is preferable to staying in the Ni-rich environment in the Ni Al GB forming P–Ni bonds. Both of the charge density and the deformation charge imply that a P atom is more likely to bond with Ni atoms rather than with Al atoms. The density of states further exhibits the interactions between P atom and Ni atom, and the orbital electrons of P, Ni and Al atoms all contribute to P–Ni bonds in the Ni Al GB. It is worth noting that the P–Ni covalent bonds might embrittle the Ni Al GB and weakens the plasticity of the Ni Al intermetallics.

Effect of P impurity on mechanical properties of NiAl Σ5 grain boundary:From perspectives of stress and energy

In this paper,we employ the first-principle total energy method to investigate the effect of P impurity on mechanical properties of NiA1 grain boundary(GB).According to"energy",the segregation of P atom in NiA1E5 GB reduces the cleavage energy and embrittlement potential,demonstrating that P impurity embrittles NiA1E5 GB.The first-principle computational tensile test is conducted to determine the theoretical tensile strength of NiA1E5 GB.It is demonstrated that the maximum idea/tensile strength of NiA1E5 GB with P atom segregation is 144.5 GPa,which is lower than that of the pure NiA1E5 GB(164.7 GPa).It is indicated that the segregation of P weakens the theoretical strength of NiA1E5 GB.The analysis of atomic configuration shows that the GB fracture is caused by the interfacial bond breaking.Moreover,P is identified to weaken the interactions between A1-A1 bonds and enhance Ni-Ni bonds.

Effect of nickel segregation on CuΣ9 grain boundary undergone shear deformations

Impurity segregation at grain boundary（GB） can significantly affect the mechanical behaviors of polycrystalline metal. The effect of nickel impurity segregated at Cu GB on the deformation mechanism relating to loading direction is comprehensively studied by atomic simulation. The atomic structures and shear responses of Cu Σ9（114） 110 and Σ9（221） 110 symmetrical tilt grain boundary with different quantities of nickel segregation are analyzed. The results show that multiple accommodative evolutions involving GB gliding, GB shear-coupling migration, and dislocation gliding can be at play, where for the 2ˉ21ˉ shear of Σ9（114） 110 the segregated GBs tend to maintain their initial configurations and a segregated GB with a higher impurity concentration is more inclined to be a dislocation emission source while maintaining the high mechanical strength undergone plastic deformation for the 11ˉ4ˉ shear of Σ9（221） 110. It is found that the nickel segregated GB exerts a cohesion enhancement effect on Cu under deformation： strong nickel segregation increases the work of separation of GB, which is proved by the first-principles calculations.