Ageing process of pre-precipitation phase in Ni_0.75Al _0.05Fe_0.2 alloy based on phase field method

By utilizing phase field method combined with analysis on free energy and interatomic potentials, pre-precipitation phase formation and transformation process of Ni_0.75Al_0.05Fe_0.2 alloy in early precipitation stage during the ageing process under 1 000 K were studied. And free energy, microstructures, compositions and volume fractions of pre-precipitation phase and equilibrium phase were analyzed. The simulation results indicate that nonstoichiometric L1₀ pre-precipitation phase formed first, and then would gradually transform into L1₂ equilibrium phase. It is discovered that the phase transformation process was closely related to free energy and interatomic potentials. Additionally, it is revealed that free energy of L1₀ pre-precipitation phase was higher and interatomic potential was smaller than that of L1₂ equilibrium phase. Therefore, it is concluded that L1₀ phase was unstable, and phase transformation would occur to L1₂ which was more stable.