Thermodynamic study on the retardation of phase transformati 2026 Next M

Oxide dispersion-strengthened (ODS) steels are promising structural materials for advanced nuclear systems because finely dispersed nanosized oxides effectively suppress dislocation, grain-boundary, and phase-boundary motion. In this study, the effect of oxide particle dispersion on the α →γ transformation behavior in 11Cr-ODS steel was investigated using a thermodynamic reference framework. Specimens with systematically varied oxide dispersion states were prepared by long-term high-temperature annealing. The transformation behavior was monitored by in-situ high-temperature X-ray diffraction, while oxide particle size and number density were characterized by transmission electron microscopy. The equilibrium A1 temperature was determined using CALPHAD-based phase equilibrium calculations, and the Δ G –Δ T relationship was constructed using literature values of the transformation entropy. Minimum driving forces required to overcome oxide particle pinning were estimated from TEM-based analysis and compared with Ac1 shifts obtained by in-situ XRD during continuous heating. Mapping these independently derived quantities onto a common Δ G –Δ T reference reveals a systematic correspondence between oxide dispersion degradation and reduced transformation resistance, providing a physically consistent interpretation of the α →γ reverse transformation in ODS steels.