Effect of boron on the structural stability, mechanical properties, and electronic structures of γ′-Ni3Al in TLP joints of nickel-based single-crystal alloys

Abstract

Boron (B) is known as a melting-point depressant for the middle interlayer to transient liquid phase (TLP) bonding of nickel-based single-crystal alloys. However, the mechanisms of B effects on structural stability, elasticity, and the electronic structures of γ′-Ni3Al remain unclear. In this work, the structural stability, mechanical properties and electronic structures of B-doped γ′-Ni3Al (the doping concentration was 0–20 at%) was investigated by employing the density functional theory. It is found that the Ni24Al8Bm (m = 0, 1, 2, 3, and 4) phases were steady-state structures, while the Ni24Al8Bm (m = 5, 6, 7, and 8) phases were non-steady-state structures. The calculated elastic constants indicated that the Ni24Al8Bm (m = 0, 1, 2, 3, and 4) phases exhibited some anisotropy, and anisotropy gradually decreased with increasing B content. Electronic structure analysis showed that the density of states and charge density were in accordance with the phonon spectra (PS) results. The changes of charge density of Ni-Al and Ni-B bonds with increasing B concentration were found to play important roles in the hardness and phase stability properties of the Ni24Al8Bm (m = 0, 1, 2, 3, 4, 5, 6, 7, and 8) phases.