First principles calculation of the effect of Pd doping on the mechanical and thermodynamic properties of Au-2.0Ni solder

To meet the demands of high-temperature usage and weight reduction in aerospace engineering, Au-Ni solder is commonly employed for dissimilar joining of Ti3Al-based alloys and Ni-based high-temperature alloys. However, the interaction between Ti and Ni results in the formation of brittle phases such as Ti₂Ni, TiNi, and TiNi₃, leading to diminished mechanical properties of the joint and potential formation of sensitive cracks during welding. Previous research has indicated that doping with Pd enhances the mechanical properties of the joint’s central region due to its strong affinity. Nevertheless, conventional experimental methods struggle to observe the microstructure of the Au-Ni-Pd solid solution phase and analyze its interface strengthening mechanism. This study employs first principles calculations based on density functional theory to assess the stability of the Au-2.0Ni-MPd (M = 0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0) alloy. The mechanical and thermal properties were assessed. The results indicate that the anisotropy of the Au-2.0Ni-MPd alloy is minimized when M is 0.5 wt.%, suggesting that 0.5 wt.% Pd effectively enhances the stability of the alloy. Specifically, when the Pd content is below 0.5 wt.%, it demonstrates higher dislocation strain energy (2.713 J m⁻¹). Furthermore, Au-2.0Ni-0.5Pd exhibits high hardness (2.629 GPa) and good toughness (Cauchy pressure = 41.796 GPa, ν = 0.364), satisfying the mechanical property requirements for brazing joints. Thermodynamic calculations demonstrate that the addition of Pd enhances the specific heat capacity of the alloy under constant volume and pressure conditions at high temperatures. The analysis of the volume–temperature and Debye temperature curves reveals that the Au-2.0Ni-0.5Pd alloy demonstrates the lowest volume change rate (8.1%) and Debye temperature slope (− 0.019) at high temperatures, suggesting reduced sensitivity to temperature fluctuations and enhanced high-temperature resistance and thermal shock fracture resistance due to Pd addition in the Au-2.0Ni material. The results demonstrate that the mechanical and thermal properties of Au-2.0Ni solder are most effectively enhanced by 0.5 wt.% Pd. This study offers theoretical guidance for further applications of Au-Ni solder in aerospace engineering.

The relationship between Debye temperature and temperature of Au-2.0Ni-Pd alloy (a) and the slope of Debye temperature (b)