Atomic-scale defect-mediated interfacial bonding in cold spray: FCC vs. BCC metal systems

The intense plastic deformation induced by the supersonic impact of powder particles during cold spray deposition determines particle-substrate interfacial properties. Herein, large-scale molecular dynamics simulations are employed to investigate the atomistic microstructural evolution of similar particle–substrate systems during impact. The focus is placed on elucidating the distinct responses exhibited by a FCC metal system (such as Al-Al) versus a BCC metal system (such as Fe-Fe) to enable a systematic comparison of deformation mechanisms, defect generation, and phase transformations intrinsic to each material type. Results indicate that the FCC system accommodates deformation through transient solid-state phase transformations from FCC to BCC and FCC to HCP, accompanied by localized interfacial rim melting and amorphization, as well as intense dislocation activity, which collectively enhance atomic intermixing and bonding. Conversely, deformation in the BCC system primarily occurs through atomic disordering and extensive twinning. At intermediate impact duration, the FCC system exhibits a significantly higher dislocation density, predominantly composed of partial dislocations. Interactions between these dislocations form sessile junctions that restrict slip and stabilize the interface. While, the BCC system is characterized by perfect dislocations closely associated with twin growth and thickening, which accommodate plastic deformation while locally limiting slip. In the final stage, both systems undergo grain refinement/recrystallization, forming new grains predominantly within the particle. Grain refinement in both systems increases grain boundary density, thereby strengthening interfacial bonding. Through these analyses, this study advances the understanding of fundamental bonding phenomena and the influence of intrinsic material properties on interfacial characteristics under solid-state deposition conditions.