Sulfur embrittlement on gamma/gamma' interface of Ni-base single crystal superalloys

摘要

The impurity sulfur embrittlement on gamma/gamma' interface of Ni-base single crystal superalloys has been investigated by first principles quantum mechanics DMol calculations. Using a local sum of vertical (SIGMA BO~v) and horizontal(SIGMA BO~h) 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 R_(BO)= SIGMA BO~h/ SIGMA BO~v 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 R_(BO) by 121 percent relative to the sulfur-free gamma/gamma' 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 gamma/gamma' interface results in reduced R_(BO), thus relieving the tendency of interface embrittlement. Furthermore, our model on sulfur embrittlement is compared with previous models.