The multiscale characterization on the phase-transformation response of the nanoscale B2 antiphase domain by the phase-field modeling

The antiphase domain (APD), having a great influence on the service performance of various superalloys occurs frequently inside the intermetallic strengthening phases. To characterize the response details (lattice evolution, elemental concentration evolution and distribution behavior) of the nanoscale APD induced by the phase-transformation variables (temperature, ternary additive, nominal composition change and lattice misfit) along the A2 to B2 path in the BCC system, the atomic scale phase-field modeling is constructed for the Fe-Al and Fe-Al-Ni. The results show that the lattice and elemental concentration of the APD evolve qualitatively in a three-stage fashion at the atomic and nanoscale, respectively. The flow of the elemental concentration is qualitatively related to the body part of the APD and varies with the atomic type, which determines the final chemical environments of the APD and the APB. Mathematically, the elemental concentration quantitatively responds as a linear function of the individual phase-transformation variable, which naturally determines the interfacial chemical environment to respond linearly. Further, the analysis of the free energy uncovers that the linear response of the elemental concentration is attributed to the synchronously regular variation of the atomic occupation configuration in the B2 unit cell. The simulation results agree well with existing experimental characterizations at the atomic and nanoscale. This work provides new quantitative and qualitative information on the evolution, partitioning and response of elements in the nanoscale B2-type APD and offers computational references in understanding, evaluating and designing superalloy properties containing the APD.