Abstract: Pourbaix diagrams are calculated to describe electrochemical processes for alloys in aqueous solution. With the multi-component differentiation of alloy systems, the construction of Pourbaix diagrams is facing challenges, especially for non-single-phase alloy systems. In this study, the simultaneous construction of phase diagrams and Pourbaix diagrams were implemented for predicting the evolution of the phases in the immune and passive regions. The CALPHAD (CALculation of PHAse Diagram) approach was used to quickly access the Gibbs free energies of various phases and the chemical potential of the elements in the phases from the thermodynamic database of the Ni-Si-Al-Y system. The corrosion behavior of two typical Ni-Al-Si and Ni-Al-Y systems was investigated. Si and Y were added to Ni-based alloys to produce the solid solutions L1_2-Ni₃(Al,Si) and L1_2-Ni₃Al + Ni₅Y, respectively. Calculations showed that NiO and Al₂O₃ make up the passive area of the Ni₃Al₁ alloy. The introduction of SiO₂ and Y(OH)₃ in the passive region separately helped to minimize the alloys' susceptibility to corrosion. However, Si reduced the thermodynamical possibility of NiO formation in the passive film, and the addition of Y caused extreme galvanic corrosion. Experiments on Ni-based alloys validated the results through electrochemical corrosion. It was also discovered that the presence of Ni₅Y produced galvanic corrosion and that Si reduced the oxide in the passive film, causing pitting corrosion. The corrosion prediction of the quaternary alloys indicates that the solid solution of Si in Ni₅Y reduces the galvanic corrosion effect and the dissolution of passive film. The current work demonstrates that phase diagrams and Pourbaix diagrams may be efficiently and accurately predicted using a well-constructed thermodynamic database, which has major implications for future studies on the corrosion behavior of multi-component alloys.

Key words: Pourbaix diagrams, CALPHAD, Ni-based alloys, Passive film