Microstructure evolution of dual-phase Fe₃₆Ni₃₆Al₁₅Cr₁₀Si₂Mo₁ multi-principal element alloy during long-term heat treatment at 700°C

FeNiAlCr multi-principal element alloys (MPEAs) have emerged as a potential candidate for applicability by virtue of their excellent mechanical properties and corrosion resistance at high temperature. The duplex nature proved to be stable after heating cycles to near melting and after aging treatments. In this work, we investigated the microstructure evolution, such as grain size, precipitate size and phase volume fraction of Fe₃₆Ni₃₆Al₁₅Cr₁₀Si₂Mo₁ alloy during long-term heat treatment at 700 °C. The corresponding mechanical properties were also considered and characterized. Experiment results indicated that the size of the L1₂ and BCC precipitates, rather than the grains, grew rapidly in the first 15 days and then entered a stage with low coarsening rate. Phase transformation of metastable L1₂ precipitates in FCC matrix phase to B2 phase occurred in this process. The coarsening and phase transformation phenomena led to the decreased strength and increased elongation of Fe₃₆Ni₃₆Al₁₅Cr₁₀Si₂Mo₁ alloy. The coarsening and phase transformation behavior of precipitates were then discussed from a thermodynamic perspective with the help of Thermo-Calc software. Using the characterization techniques of SEM/EBSD/TKD and detailed analysis, this research clarified the microstructure evolution process and may provide potential guidance for the phase stability of MPEAs in industrial applications.