Defeating phase boundary-induced internal oxidation via eliminating interfacial Al segregation in D0₁₉-strengthened high-entropy alloys

Internal oxidation severely limits the high-temperature reliability of precipitation-strengthened high-entropy alloys (HEAs), yet the role of phase boundary chemistry remains unclear. Here, we demonstrate that pronounced Al segregation at lamellar D0₁₉ phase boundaries triggers severe internal oxidation by creating preferential oxygen transport pathways and disrupting the continuity of the Al₂O₃ scale. Thermomechanical processing effectively eliminates this undesired segregation through high-strain serrated phase boundaries with dense dislocation networks, enabling the homogeneous interfacial chemistry and associated improved oxidation resistance at 800 ℃, with the parabolic rate constant reduced from 2.06 × 10⁻⁴ to 7.12 × 10⁻⁵ mg²·cm⁻⁴·h⁻¹. The results demonstrate that phase boundary segregation governs oxidation transport behavior, establishing interface engineering as a promising microstructure engineering approach to suppress internal oxidation in precipitation-strengthened alloys.