Papers by Author: Li Qun Chen

Abstract: NiAl is one kind of high-temperature alloys with broad potential applications in aerospace industry. Its mechanical properties are believed to be largely related to the dislocation behavior and impurity-dislocation interaction. In the paper we report first principles study of the alloying effect of Zr in the [10(010) edge dislocation core of NiAl. The binding energy of doping system decreases 3.77 eV when a Zr atom substituted for an Al, only decreases 1.06 eV with substitution for a Ni atom. The result of the binding energy shows that a Zr atom prefers to occupy an Al site in the dislocation core of NiAl. The analyses of the charge distribution, the interatomic energy and the partial density of states suggest that Zr will greatly enhance the interaction between Zr atom and neighboring host atoms, as well as that between host atoms. These results show that the alloying element Zr induced pinning effect on the edge dislocation motion is predicted, and could be helpful for understanding microscopic mechanisms of alloying-induce hardening in NiAl alloy.

Abstract: The effect of light impurities (C, N) upon the electronic structure of the [100](010) edge dislocation core in NiAl single crystals is investigated by using the Dmol and the discrete variational method within the framework of density functional theory. The impurity segregation energy, interatomic energy and charge distribution are calculated, and the effects of impurity atoms upon the dislocation motion are discussed. The energy analysis shows that both C and N atoms can stabilize the [100](010) edge dislocation core, and prefer to occupy the interstitial site in the Center-Ni dislocation core. Meanwhile, the impurity atoms can form strong bonding states with their neighboring host atoms via hybridization between the 2p orbitals of the impurity atom and the 3d4s4p orbitals of the host Ni atoms; as well as between the 2p orbitals of the impurity atom and the 3s3p orbitals of the host Al atoms. The strong interaction between impurity atom and host atoms in the dislocation core may improve the strength of NiAl single crystals.

Abstract: The optimal geometries and mechanical properties of a kink with P are studied by applying density functional theory to the ½[111](1¯10) edge dislocation in bcc iron. The calculated impurity segregation energy shows that the P atom can be potentially trapped by the kink, and the doping P preferably segregates to the core region of the ½[111](1¯10) edge dislocation rather than to the <100>(010) edge dislocation. The analysis of the electronic structure indicates that the sideward motion of the kink is impeded owing to strong a interaction between P and neighboring Fe atoms. That is, the P induces a pinning effect on the ½[111](1¯10) edge dislocation. The hybridizations between P and Fe come from P 3p and Fe 3d4s4p. The p and d states have an obvious orientation, which may not be favorable to the toughness of iron. The localized effect of the P-kink complex distinctly affects the electronic structure as well as the energy of the system.

Abstract: By the use of the first-principles method, based upon density functional theory, we investigated the effect of C upon the electronic structure of a kink on the ½[111](1¯10) edge dislocation in bcc iron. The results show that C has a tendency to segregate towards the kink. The structural energies of some atoms of interest in the kink with C are lower than those of corresponding atoms in the clean kink. Furthermore, the interactions between C and the neighboring Fe atoms are very strong due to the hybridization between the C 2p state and the Fe 3d4s4p states. We find that there exists some charge accumulations between C and the neighboring Fe atoms. The analysis of the electronic structure indicates that the introduction of C can stabilize the kink system and impede the sideways motion of the kink. The C induces a strong pinning effect on the ½[111](1¯10) edge dislocation and may result in solid solute hardening.

Abstract: Using the first-principles self-consistent discrete variational method based on density functional theory, we investigated the energetics and the electronic structure of 3d impurity Mn and Cr in the kink on the [100](010) edge dislocation in bcc iron. The calculations of binding energies show that both Mn and Cr can stabilize the system containing kink. We also calculate the structural energy, the interatomic energy, the local density of states and the charge density difference. The results indicate that both Mn and Cr in the kink can enhance the interatomic interaction between the impurity atom and the neighboring Fe atoms due to the hybridization of impurity d-Fe d orbitals. The introduction of the Mn and Cr impurity leads to a strong pinning effect on the dislocation motion in bcc iron, which may explain the solid solute hardening of Mn and Cr.

Abstract: Using the first-principles self-consistent discrete variational method based upon density functional theory, we investigated the energetics and the electronic structure of the 3d impurities Ni and Co in a kink on the [100](010) edge dislocation (ED) in bcc iron. The calculated results show that the interatomic energies between the impurity atom and the neighboring host atoms decrease. The bonding for the impurity atom (Ni, Co) and the neighboring host Fe atoms is weaker than that for an Fe atom at the X site and the corresponding atoms in the clean kink. These results indicate that sideways motion of the kink in the <100>{010} ED is accelerated by an impurity atom such as Ni or Co and that, consequently, the presence of impurities increases the dislocation mobility, thus leading to solid-solution softening.