Influence of grain structure and crystallographic orientation on fatigue crack propagation behavior of 7050 alloy thick plate

• Anisotropy of fatigue growth rate is different from strength and toughness.
• Fatigue behaviors are analyzed based on crystallographic model and Schmid factors.
• Twist angle differences determine the intergranular or transgranular propagation.
• Crack deflection and branch depend on slip systems and loading stress.

Fatigue crack propagations of 7050 alloy thick plate in different orientations were investigated. Anisotropy of fatigue property showed some difference compared to that of strength and toughness. Microstructural observations revealed that the anisotropy was significantly influenced by structure and orientation characteristics of recrystallized grains. Detailed analysis based on crystallographic model and Schmid factors suggested that the fatigue behaviors, including inter/transgranular propagation, crack deflection or bifurcation, depend on crystallographic orientations and geometry of local microstructure, particularly the tilt and twist angle differences of slip planes or crack planes, together with cooperation and competition between movement of slip systems and loading stress.