Effect of refractory elements M (=Re, W, Mo or Ta) on the diffusion properties of boron in nickel-based single crystal superalloys

Abstract

Boron (B) is known as a melting-point depressant for the middle interlayer to transient liquid phase (TLP) bonding of the nickel-based single crystal superalloys (Ni-SCS). However, the mechanisms for the effect of refractory elements M (=Re, W, Mo or Ta) on B diffusion in Ni-SCS remain unclear till now. Thus, the refractory elements M (=Re, W, Mo or Ta)'s effects on the diffusion of B in Ni-SCS is investigated using the density functional theory in this paper. It is found that Mo and Re atoms are mainly distributed in the γ-Ni phase, while majority of W and Ta atoms are mostly located in the Al site in γ′-Ni3Al phase. The octahedral interstices of γ-Ni and γ′-Ni3Al are preferentially occupied by B atoms. The results indicate that the M (=Re, W, Mo or Ta) atoms doped in the structures prevent B diffusion, and the change trend of B diffusion E(BFP) follows Re < Mo < W < Ta. Electronic structure analysis shows that the different atomic radiuses from Re to Ta and different hybrid orbitals between M d and B 2p from Re to Ta play important roles in the diffusion properties of B in the nickel-based single crystal superalloys.