Microstructural Evolution and its Effect on the Mechanical Properties of a Novel Second‐Generation Single Crystal Superalloys After Thermal Exposure

In gas turbines, critical components such as turbine blades operate under prolonged high‐temperature conditions, which often result in the degradation of the microstructure in a nonuniform manner. In the article, the relationship between the microstructural evolution and mechanical properties of a novel second‐generation nickel‐based single‐crystal superalloy subjected to extended thermal exposure at 900 °C is examined. The results demonstrate that, with increasing the duration of thermal exposure, the γ′ phase size increases from 0.35 μm (0 h, edge length) to 0.46 μm (1000 h, thickness), transitioning from a regular cubic shape to a rafting structure. The tensile properties of the alloy first increase and then decrease. The coarsening behavior of the γ′ phase in the tested alloy aligns with the Lifshitz–Slyozov–Wagner theory (LSW), with a coarsening rate constant of 5.51 × 10 4 nm 3 h −1 . Additionally, the Kirkendall effect, driven by the uneven diffusion of alloying elements, results in a rise in both the quantity and size of micropores. Microcracks are more likely to start and spread from the pointed corners of micropores. The coarsening of the γ′ phase, combined with the growing presence of large, irregularly shaped micropores, ultimately contributes to the degradation of the alloy's tensile properties.