Effect of Low-Angle Grain Boundaries on High-Temperature Fatigue Crack Behavior in DD413 Nickel-Based Superalloy

Fatigue behavior of low-angle grain boundaries (LAGBs) in a DD413 single-crystal (SX) superalloy was systematically investigated at 900 °C using EBSD, XCT, and fracture analysis. Tilt-I boundaries exhibited the highest fatigue life (>10 7 cycles), maintaining ordered γ′ morphology and achieving four times the fatigue life of Twist boundaries. With increasing misorientation from 4.8° to 17.8°, fatigue life decreased markedly by ~80%, with a critical transition occurring in the misorientation range of ~10-13°. Three-dimensional XCT revealed a transition from transgranular cracking at low angles to carbide-assisted interfacial fracture at higher angles. A composite stress concentration model (K t ) was proposed to unify the roles of boundary type and misorientation in controlling crack evolution, enabling quantitative prediction of fatigue life. These findings highlight that optimizing LAGBs toward Tilt-I configurations with misorientation <10° can significantly improve the fatigue resistance of turbine blade alloys. • Tilt-I LAGBs show superior fatigue resistance due to high slip compatibility. • Fatigue life decreases by ~80% as misorientation increases from 4.8° to 17.8°. • A composite Kt model quantifies LAGB effects through GND density and geometry. • 3D XCT reveals late-stage cracks propagate along carbide–matrix interfaces. • Results provide guidelines for grain boundary engineering to enhance fatigue life.