High-temperature oxidation behavior of a single-crystal high-entropy superalloy strengthened by dense intermetallic nanoparticles

The oxidation behavior of a newly developed single-crystal L1₂-strengthened Co-rich high-entropy superalloy, Co₄₁Ni35Al_11.5Ta_2.5Cr₄Ti₆ (at%), was investigated systematically in air at 800, 900, and 1000°C. The results reveal that this alloy demonstrates excellent oxidation resistance from 800 to 1000°C. At 800°C, a bilayer oxide scale was formed, consisting of a TiO₂/Al₂O₃ mixture layer and a Cr₂O₃ layer. The continuous but non-dense Cr₂O₃ layer could not effectively inhibit internal oxidation and internal nitridation. Complex hierarchical-structure oxide scale formed at 900 and 1000°C, mainly composed of spinels, Cr₂O₃, TiTaO₄, and Al₂O₃. Surprisingly, an anomalous improvement in oxidation resistance was found in a temperature range from 900 to 1000°C. Specifically, the formation of a more complex and continuous five-layer oxide scale at 1000°C, particularly the bottom compact Al₂O₃ layer, endows the alloy with exceptional resistance to oxidation at 1000°C.[Figure not available: see fulltext.]