Enhancing mechanical and tribological properties of laser-based directed energy deposited IN718 alloy via synchronised high repetition laser shock peening

Laser-based direct energy deposition (LDED) has been restricted by unavoidable defects and poor mechanical performance. This study proposes synchronised high repetition laser shock peening (HRLSP) to modify the mechanical and tribological properties of IN718 alloy. After layer-by-layer HRLSP treatment, the densification increased to 99.5%. The average grain diameter decreased by 30.8% with a specified strong texture in the microstructure. Superior strength at various strain rates and enhanced wear resistance were achieved. At the strain rate of 0.01 s(-1), the ultimate tensile strength (UTS) and elongation reached 897 MPa and 24%, respectively. The improved strength was largely ascribed to Hall-Petch, compression residual stress, precipitation, and dislocation strengthening. The numerical results demonstrate that the laser shock wave effectively regulates the residual stress and introduces high-density dislocations that are sensitive to higher temperatures and compression velocity. This study provides a novel insight into utilising HRLSP to form high-performance LDED-built IN718 alloy.