Quantifying the impact of oxidized carbide expansion on fatigue crack initiation in a Ni-based single-crystal superalloy

Abstract

Carbide oxidation is commonly observed near fracture surfaces of superalloys under atmospheric fatigue conditions. Here, we investigated how MC carbide oxidation affects crack initiation in single-crystal superalloys during intermediate-temperature low-cycle fatigue. The findings reveal that an oxide layer composed of nanocrystalline anatase-TiO₂ and B-Ta₂O₅ formed within the carbides, triggering local lattice rotations in the surrounding matrix that exceeded 15° and GND densities above 4 × 10¹⁵ /m², likely due to multislip. First-principles calculations and finite element analysis revealed that (i) the formation of the oxide layer can cause approximately 28.5 % expansion of the carbide lattice, and (ii) the resulting thermal stress along with oxidation primarily concentrates near the oxide and carbide interface. A physical model is proposed to explain how carbide oxidation facilitates fatigue crack initiation in single-crystal superalloys under cyclic loading.