High‐Temperature Oxidation of the CrFeNi Medium‐Entropy Alloy

The isothermal high‐temperature oxidation behavior of the equiatomic CrFeNi medium‐entropy alloy is a key issue that determines whether this material is suited for high‐temperature application. In this view, the understanding of the long‐term behavior is even more crucial than short‐term corrosion effects. Herein, a single‐phase CrFeNi alloy of the face‐centered‐cubic structure is exposed to synthetic air at 1000, 1050, and 1100 °C for 24, 100, and 1000 h and its oxidation behavior is systematically compared to that of 316L steel, which shows a surprising initial oxidation stabilization during early stages. The oxidation rate of CrFeNi is parabolic at 1000 °C (with a parabolic constant k _p = 1.4·10 ⁻⁵ mg ⁻² cm ⁻⁴ s ⁻¹ ) and 1050 °C ( k _p = 2.7·10 ⁻⁵ mg ⁻² cm ⁻⁴ s ⁻¹ ), but breakaway oxidation occurs at 1100 °C after 4 h of exposure. In all cases, the oxide scales are found to (at least) partially spall off. Chromium diffuses outward to form a Cr ₂ O ₃ layer at the gas/oxide interface, and a thin layer of (Cr, Fe, Ni) ₃ O ₄ is identified at the oxide/alloy interface. Unlike the 316L alloy, which contains more Mn and Fe, the CrFeNi alloy does not show any catastrophic oxidation behavior at the investigated conditions.