Microstructure evolution and performance improvement of 42CrMo steel repaired by an ultrasonic rolling assisted laser directed energy deposition IN718 superalloy

Laser direct energy deposition (LDED) has emerged as a notable additive manufacturing technology, garnering significant interest for the production and repair of components. However, the utilization of LDED for part repair is associated with several issues, such as the presence of defects, the tendency to form columnar grains, and poor bonding between dissimilar materials. These issues ultimately compromise the mechanical properties of the components. To address these challenges, this study proposes an ultrasonic rolling assisted laser direct energy deposition method and establishes a dedicated process platform for depositing IN718 superalloy onto a 42CrMo substrate for repair purposes. The effects of ultrasonic rolling on bond strength, porosity, microstructure evolution, and mechanical properties of the repaired specimens were investigated, and the microstructure evolution mechanism during ultrasonic rolling was explored. The results show that ultrasonic rolling reduces defect size and quantity, refines grain structure, enhances the metallurgical bonding of dissimilar materials, and generates numerous low-angle grain boundaries with high dislocation density. The hardness of UR-LDED specimens was increased by about 17 % compared to LDED specimens. The yield strength and ultimate tensile strength along the X-direction increased from 661.7 MPa to 732.5 MPa and 856.1 MPa to 920.2 MPa, respectively, with a slight decrease in elongation. The yield strength and ultimate tensile strength in the Y-direction increased from 643.6 MPa to 736.7 MPa and 826.4 MPa to 897.5 MPa, respectively, and the elongation increased.