Thermal-mechanical coupled regulation of Ti-22Al-25Nb/Ti-6Al-4V bimetallic structures during an alternating ultrasonic surface rolling – laser directed energy deposition hybrid process

Although bimetallic structures have demonstrated great thermomechanical compatibility under extreme temperature gradients, the poor bonding performance and damage resistance still hinder wider application. In this study, an alternating ultrasonic surface rolling process-laser directed energy deposition (USRP-LDED) hybrid process is proposed to enhance the bonding performance and fracture toughness of Ti-22Al-25Nb/Ti-6Al-4V bimetallic structure based on thermal-mechanical coupled regulation. The study revealed the anisotropic bending response of the bimetallic structure and demonstrated that the hybrid process significantly enhances the fracture toughness under different loading modes. Additionally, the coordinated matching of multi-regional microstructures further enhances bonding strength by 31.4%. Consequently, the thermal-mechanical regulation mechanism was elucidated and decoupled through systematic deconstruction analysis. For the deposition region, the stress-dominated crystal continuity destruction and the precipitation inhibition caused by thermal regulation increased the stress intensity factor to 38.1 MPa·m¹/². For the substrate region, interlayer USRP suppressed the brittleness effect in the heat-affected zone, increasing the elongation by 37% while suppressing α’ phase coarsening. For the transition zone, interlayer USRP reduces elemental diffusion through attenuated heat input while significantly improving bonding strength by refining the α2 phase.