Diffusion-induced phase transformations across the γ-loop in the Fe–Cr system

Journal article, 2026

Interdiffusion and diffusion-induced phase transformations around the γ-loop in the Fe–Cr system were investigated using diffusion couples between Fe–Cr alloys (10 and 18 wt% Cr) and pure Fe at 800–1000 °C. New phase layers form when the diffusion path intersects the γ-loop. At 1000 °C, a ferrite layer grows into the austenitic Fe–10Cr side, whereas at 900 °C, an austenitic layer forms in the initially ferritic Fe–18Cr / Fe couple. DICTRA simulations accurately reproduce concentration profiles, phase distributions, and interface positions without adjustable parameters. Classical Wagner-type analysis quantitatively reproduces interdiffusion coefficients in both BCC and FCC phases based on the measured phase growth kinetics. The results provide direct experimental evidence of diffusion-induced α→γ transformation driven by chromium depletion and establish its role in accelerated oxidation of Fe–Cr alloys at 900 °C and above.