Multiscale mechanisms of residual stress evolution and cyclic loading inspired cracking in laser additively manufactured TC11 large-scale components

Regulating the residual stress during the laser powder-directed energy deposition (LP-DED) process of large-scale and complex components in aerospace field exists a significant challenge. Herein, we propose to solve this critical problem by reducing the defects, minimization of sharp-angular structural features and adjusting the basketweave microstructure. The large-scale TC11 spacecraft components were manufactured by LP-DED process. Through the fracture morphology analysis and macroscopic thermal–mechanical coupling finite element calculation, the loading mode of residual stress during the LP-DED process is obtained as an asymmetric cyclic loading mode, including stable cycle-burst, nonlinear cyclic and linear cyclic stage. The stress concentration caused by defects and geometric shapes is usually the main reason for residual stress-induced crack initiation. Through crystal plasticity calculation, the coarse basketweave with appropriate lamellar thickness has the best crack resistance of asymmetric loading residual stress. In addition, the linear cyclic loading mode has the largest damage driving force, with the strain localization and stress concentration being the origin of crack initiation and propagation. Under the condition of asymmetric cyclic loading, the Widmanstätten microstructure forms the initiation point of lamellar crack, expanding along the long axis of α lamellae. The basketweave microstructure forms a dot crack initiation point at the cross position of the α lamellae and propagates by interconnecting. This work provides new insights into the evolution mechanisms of residual stress during LP-DED process, and provides theoretical guidance for reducing the residual stress in large-scale components.