Effects of Re, W and Co on dislocation nucleation at the crack tip in the γ -phase of Ni-based single-crystal superalloys by atomistic simulation

Abstract

The effects of Re, W and Co on dislocation nucleation at the crack tip in Ni have been studied by the molecular dynamics method. The results show that the activation energy of dislocation nucleation is lowered by the addition of Re, W and Co; moreover, the activation energy decreases when the alloying element increases from 1 at.% to 2 at.%. The energy landscapes of the atoms are studied to elucidate these effects. Quantification analyses of the bonding strength between Ni and X (X = Re, W or Co) reveal that strong bonding between Ni and X (X = Re, W or Co) in the dislocation nucleation process can suppress the cleavage process and enhance the ability of dislocation nucleation. The surface energy and unstable stacking fault energy are also calculated to understand the alloying effects on the dislocation nucleation process. The results imply that interaction between alloying elements and Ni atoms plays a role in promoting the dislocation nucleation process at the crack tip. The ability of Re, W and Co in improving the ductility of the Ni crack system is in the order W > Re > Co. The results could provide useful information in the design of Ni-based superalloys.

Molecular dynamics simulations of dopant effects on lattice trapping of cracks in Ni matrix*

“…To further investigate the strengthening mechanisms of the doped Ni crack system, we used MD simulations to calculate the average atomic (E eatom ) and surface (γ) energies (see Fig. 5), defined below: [4,7,13,29]…”

“…[1,2] The γ-Ni phase is a popular host matrix for the Ni-based SC superalloys as it affects the overall mechanical properties of the resulting materials, [2,3] while the crack in γ phase restricts its applications. Analysis of the γ phase microstructure evolution was reported [4][5][6][7] earlier. However, the fracture in superalloys are complex, and the strengthening mechanism of γ-Ni matrix is still not very clear.…”