Segregation of Re at theγ/γ'boundary of Ni-based single crystal superalloys revealed by first-principles calculations based Monte-Carlo simulations

Nickel-based single crystal superalloys have been widely used in aero-engines and gas turbine engines.To improve the creep resistance,rhenium is often added to the alloys.However,it is not yet fully under-stood how the added Re elements distribute in the alloys and how the microstructure evolves with the addition of Re.Here,we performed extensive first-principles calculations based Monte-Carlo simulated annealing of Ni-Al-Re ternary alloys with different Re concentrations ranging from 0.5 at.%to 6.0 at.%.The results demonstrate that with the decreasing temperature,most of Re atoms stay in theγphase,while a few of Re atoms stay in theγ'phase and tend to occupy the Al positions.At low temperatures,the Re atoms segregate at theγ/γ'boundary,in good agreement with experiment.We find that the disorder-order transition temperature of the Ni-Al-Re ternary alloys increases with the Re concentration due to the Re-enhanced Al-Al ordering tendency.In addition,we observe that at low temperatures the Re segregation at theγ/γ'boundary promotes the formation of Ni 4 Re-or Ni 8 Re-like local structures as the Re concentration is over 2 at.%.The formation of a large amount of these local structures consumes the Re atoms in solid solutions,and thus from the solid-solution strengthening point of view,this would have a negative influence on the creep resistance of the superalloys.This work provides important atomistic insights on the Re distribution and its effects on the stability of superalloys.