Atomistic insights into enhanced plastic deformation and diffusion in laser- and ultrasound-assisted cold spray of Ni–Cr–Co alloy

Nickel (Ni)–Chromium (Cr)–Cobalt (Co) medium-entropy alloys are well known for their excellent mechanical strength, toughness, and thermal stability under extreme service conditions. Solid-state cold spray additive manufacturing (CSAM) has emerged as a promising route for manufacturing and repairing these alloys by eliminating melt-related defects through high-velocity kinetic bonding. However, achieving effective in situ alloying during CSAM requires enhanced atomic diffusion while preserving the advantages of the solid-state process. In this work, atomic-scale simulations are employed to investigate the effects of ultrasonic excitation, laser post-treatment, and substrate heating on the deformation and diffusion of Ni, Cr, and Co particles deposited on a polycrystalline Ni substrate. The results show that ultrasonic excitation enhances plastic deformation through the acoustoplastic effect, whereas laser irradiation and substrate heating significantly promote atomic diffusion required for alloy formation. A nonlinear increase in atomic diffusivity with laser intensity is observed while maintaining temperatures below the melting points of the constituent elements. Furthermore, process maps reveal that laser intensity primarily governs diffusion, while ultrasonic excitation provides a complementary enhancement in plastic deformation, highlighting the distinct roles of thermal and mechanical assistance during CSAM. Overall, this study elucidates the complementary roles of mechanical and thermal assistance in enabling in situ alloying during CSAM and provides fundamental mechanistic insights for optimizing externally assisted solid-state additive manufacturing processes.