Low‐Angle Grain Boundaries in Ni‐Based Single‐Crystal Superalloys: Formation Mechanisms, Microstructural Features, and Mechanical Properties

Low‐angle grain boundaries (LAGBs) are critical crystallographic defects that form during directional solidification of Ni‐based single‐crystal superalloys and remain a key factor limiting the reliability of aero‐engine turbine blades. Unlike conventional grain boundaries in polycrystals, LAGBs in single‐crystal superalloys originate from cumulative dendrite misorientations induced by thermal/solute stresses and interdendritic melt convection, evolving into tilt or twist configurations characterized by distinct dislocation networks. Despite decades of investigation, the mechanistic understanding of LAGB formation, evolution, and associated deformation behavior remains incomplete, particularly regarding the coupling between microstructural development and mechanical degradation. In this review, we comprehensively summarize recent progress in LAGB research, emphasizing (i) atomic‐scale characterization of boundary structure and chemistry, (ii) solidification‐driven formation mechanisms linked to dendritic deformation under process‐induced stresses, (iii) microstructural signatures including orientation gradients, solute segregation, and γ/γ′ topology, and (iv) the effects of LAGBs on mechanical performance. Furthermore, we analyze composition‐ and process‐ based mitigation strategies, including microalloying with B, C, Hf, and Zr to enhance boundary cohesion and damage tolerance. This review aims to provide a mechanistic framework for LAGB control and guide the development of defect‐tolerant next‐generation single‐crystal superalloys.