High temperature damages of Ni-base-superalloy caused by the change of nanotexture due to strain-induced anisotropic diffusion

In order to assure the reliability of advanced gas turbine systems, it is very important to evaluate the damage of high temperature materials such as Ni-base superalloys under creep and fatigue conditions quantitatively. Since the micro texture of the gamma-prime (γ') phase was found to vary during the creep damage process, it is possible, therefore, to evaluate the creep damage of this material quantitatively by measuring the change of the micro texture. The mechanism of the directional coarsening of γ' phases (rafting) of Ni-base superalloy under an uni-axial strain at high temperatures was analyzed by molecular dynamics (MD) analysis. The stress-induced anisotropic diffusion of Al atoms perpendicular to the initially finely dispersed γ/γ' interface in the superalloy crystal was observed clearly in a Ni(001)/Ni ₃Al(001) interface structure. The stress-induced anisotropic diffusion was validated by experiment using the stacked thin films structures which consisted of the (001) face-centered cubic (FCC) interface. The reduction of the diffusion of Al atoms perpendicular to the interface is thus, effective for improving the creep and fatigue resistance of the alloy. It was also found by MD analysis that the dopant elements in the superalloy also affected the straininduced diffusion of Al atoms. Palladium was one of the most effective elements which restrain Al atoms from moving around the interface under the applied stress.