Enhancement effect of Ni on the mechanical and thermodynamic properties of Au-xNi (x = 0.5,1.0,1.5,2.0,2.5,3.0) alloy: a first-principles study

Abstract Au-17.5Ni is a high-performance solder extensively utilized in the assembly of satellites, aircraft engines, and ceramic components, owing to its exceptional high-temperature properties. However, its inherent brittleness renders it susceptible to defects such as fractures, cracking, and delamination during the manufacturing of welding wires and foils. To mitigate these challenges, this study employs first-principles calculations to investigate the structural stability, mechanical properties, and thermal behavior of the primary phase in the Au-17.5Ni alloy, with a particular focus on the Au-rich phase, a solid solution of Ni in Au. The results indicate that the Au-2.0Ni composition exhibits the highest plasticity, characterized by a Pugh’s ratio (B/G) of 7.671 and a hardness value of 0.643 GPa, representing a 31.76% increase compared to pure Au. These improvements significantly enhance the processing performance of the Au-17.5Ni alloy. Moreover, the constant pressure specific heat capacity (C p ) of Au-xNi alloys exceeds that of pure Au and increases with higher Ni content. At 800 K, the Au-3.0Ni alloy exhibits the highest C p at 31.179 J mol −1 ·K −1 , indicating improved high-temperature stability. Additionally, the thermal expansion coefficients for Au-1.0Ni, Au-2.0Ni, and Au-3.0Ni increase by 13.037%, 22.858%, and 38.097%, respectively, which may lead to elevated thermal stresses in welded joints. Consequently, maintaining the Ni content in the Au-rich phase of the Au-17.5Ni solder below 2.0 wt% can significantly enhance solder processability, ultimately improving the yield of welding wires and foils.