Zirconium (Zr) element doping has proven to be an effective strategy for reinforcing the strength and toughness of Pt-Rh alloys. However, the incorporation of Zr into Pt-Rh alloy in solid solution form renders its microstructural observation challenging through experimental means, thus complicating the elucidation of its underlying mechanisms. Therefore, this study employs density functional theory-based first-principles calculations to investigate the mechanical and thermodynamic properties of Pt-40Rh-xZr (x = 0, 0.1, 0.5, 1.0) alloys. The results reveal that with an increasing Zr weight percentage, Young’s modulus, and hardness of Pt-40Rh-xZr alloys exhibit a trend of an initial decrease followed by a subsequent increase. Notably, at a Zr weight percentage of 1.0 wt.%, the alloy Pt-40Rh-1.0Zr demonstrates the highest Young’s modulus (329.119 GPa) and hardness (10.590 GPa). Concurrently, thermodynamic calculations indicate that as Zr content increases, the crystal thermal stability of Pt-40Rh-xZr alloys initially decreases before rising again. More specifically, the coefficient of thermal expansion for Pt-40Rh-1.0Zr is merely 89.518% of that observed in Pt-40Rh. These results imply that incorporating 1.0 wt.% Zr results in the most substantial enhancement in the comprehensive mechanical properties of the Pt-40Rh-xZr alloy. Consequently, this study offers theoretical insights that can guide the extended application of Pt-Rh alloys.

To meet the demands for high-temperature performance and lightweight materials in aerospace engineering, the Au-Ni solder is often utilized for joining dissimilar materials, such as Ti₃Al-based alloys and Ni-based high-temperature alloys. However, the interaction between Ti and Ni can lead to the formation of brittle phases, like Ti₂Ni, TiNi, and TiNi₃, which diminish the mechanical properties of the joint and increase the risk of crack formation during the welding process. Cu doping has been shown to enhance the mechanical properties and high-temperature stability of the Au-Ni brazed joint’s central area. Due to the difficulty in accurately controlling the solid solution content of Cu in the Au-Ni alloy, along with the high cost of Au, traditional experimental trial-and-error methods are insufficient for the development of Au-based solders. In this study, first principles calculations based on density functional theory were employed to analyze the effect of Cu content on the stability of the Au-2.0Ni-xCu (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 wt%) alloy phase structure. The thermal properties of the alloy were determined using Gibbs software fitting. The results indicate that the Au-2.0Ni-0.25Cu alloy exhibits the highest plastic toughness (B/G = 5.601, ν = 0.416, Cauchy pressure = 73.676 GPa) and a hardness of 1.17 GPa, which is 80% higher than that of Au-2.0Ni. This alloy balances excellent strength and plastic toughness, meeting the mechanical performance requirements of brazed joints. The constant pressure specific heat capacity (C_p) of the Au-2.0Ni-xCu alloy is higher than that of Au-2.0Ni and increases with Cu content. At 1000 K, the C_p of the Au-2.0Ni-0.25Cu alloy is 35.606 J·mol⁻¹·K⁻¹, which is 5.88% higher than that of Au-2.0Ni. The higher C_p contributes to enhanced high-temperature stability. Moreover, the linear expansion coefficient (CTE) of the Au-2.0Ni-0.25Cu alloy at 1000 K is 8.76 × 10⁻⁵·K⁻¹, only 0.68% higher than Au-2.0Ni. The lower CTE helps to reduce the risk of solder damage caused by thermal stress. Therefore, the Au-2.0Ni-0.25Cu alloy is more suitable for brazing applications in high-temperature environments due to its excellent mechanical properties and thermal stability. This study provides a theoretical basis for the performance optimization and engineering application of the Au-2.0Ni-xCu alloy as a gold-based solder.

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.