Electromagnetic Compound Field Enhances Surface Strengthening and Plasticity in Ultrasonic Nanocrystal Surface Modification of Ti64 Alloy

Abstract Surface severe plastic deformation (SSPD) techniques have been widely used to enhance the surface integrity and mechanical performance of metallic materials via modifying surface microstructures and introducing compressive residual stress. In this study, we applied an electromagnetic (EM) compound field to assist a deformation-based surface strengthening technique known as ultrasonic nanocrystal surface modification (UNSM). EM-assisted UNSM outperforms its electric- or magnetic-assisted counterparts by producing a synergistic effect during processing, which leads to significant improvements in the surface hardness and the depth of the compressive residual stress layer in Ti64. X-ray diffraction (XRD) analysis and viscoplastic self-consistent (VPSC) modeling further revealed that the EM field promotes the activation of ⟨c+a⟩ dislocations, which facilitates strain accommodation and weakens crystallographic texture. These findings provide new insights into plasticity control of hard-to-deform metals, with promising implications for advanced forming and surface treatment technologies.