Grain boundary oxidation in iron-based alloys, investigated by 18O18O enriched water vapour – The effect of mixed oxides in binary and ternary Fe–{Al, Cr, Mn, Si} systems

• Selective oxidation at 700 °C in iron-based model alloys.
• Variation of the oxygen isotopes (16O/18O)(16O/18O) to determine fast diffusion pathways.
• Mn containing ternary alloys show severe grain boundary oxidation.
• Grain boundary oxidation similar to theoretical results but bulk oxidation smaller.
• Substitution between bound (oxide) and mobile oxygen observed in Mn-free alloys.

Selective oxidation experiments at 700 °C in binary and ternary iron-based model alloys containing Al, Cr, Mn, and Si were carried out. The internal oxidation behaviour along grain boundaries and inside ferrite grains was analyzed by LOM, SEM and ToF-SIMS. Oxygen isotope exchange revealed the location of fast diffusion pathways in the alloy. Numerical calculations of oxide distributions were compared to experimental findings, revealing that oxygen transport within ferrite grains is significantly lower than reported from literature. Discrepancies between simulations and experiments were discussed. The presented hypothesis of oxygen trapping represents an important viewpoint to explain internal oxidation in metallic alloys.