Kuiying Chen

Sulfur embrittlement on γ/γ′ interface of Ni-base single crystal superalloys

Abstract The impurity sulfur embrittlement on γ/γ′ interface of Ni-base single crystal superalloys has been investigated by first principles quantum mechanics DMol calculations. Using a local sum of vertical (∑BOv) and horizontal (∑BOh)Mayer bond orders, we proposed a new method to evaluate the competition between the shear and cohesive strengths of the interface. Coupled with the phenomenological theory of fracture, we define the ratio of RBO=∑BOh/∑BOv to assess the embrittlement trend of the interface related to sulfur doping or sulfur doping combined with Re substitution. It is shown that sulfur increases RBO by 121% relative to the sulfur-free γ/γ′ interface, which could induce interface embrittlement from the electron bonding point of view. Calculations of both BO and charge density distribution reveal that it is the strong bonds between sulfur and Ni atoms lying within the interface that contribute to the interface embrittlement. The substitution of Re for Al at the γ/γ′ interface results in reduced RBO, thus relieving the tendency of interface embrittlement. Furthermore, our model on sulfur embrittlement is compared with previous models.

Synergetic effect of Re and Ru on γ/γ′ interface strengthening of Ni-base single crystal superalloys

Abstract The synergetic effect of Re and Ru on γ/γ′ interface strengthening of Ni-base SC superalloys has been investigated by performing DMol3 calculations. Results show that the synergetic effect of Re and Ru on the interface strengthening is better than that achieved by the individual Re or Ru due to Re-d/Ru-d, Re-d/Ni-d and Ru-d/Ni-d hybridizations. The electronic mechanism underlying the synergetic effect of Re and Ru on γ/γ′ interface strengthening is related to the charge transfer of electrons and the enhancement of d-bonding hybridization among ReRu, ReNi and RuNi atoms.

Electronic origin of anomalously high shear modulus and intrinsic brittleness of fcc Ir

Through ab initio density functional theory based calculations, we find that the anomalously large shear modulus and the intrinsic brittleness of face-centred cubic (fcc) iridium (Ir) are primarily a consequence of its relatively strong bonds. Comparative analysis of the bond order, which dictates the bond strength, the localization of the valence electrons and the elastic constants of Ir and a selection of fcc metals allows us to rationalize the peculiarities of Ir in terms of its strong and directional bonds. Furthermore, the similarities between the failures of Al and Ir are suggested to reflect the resemblance existing between the angular features of their bonds.