Studies of single-particle impact

Cold spray (CS) manufacturing is accomplished by the sequential consolidation of sprayed solid microparticles (μPs) via collision-induced extreme plastic deformation of μPs with a substrate or other consolidated μPs. Due to the extreme deformation originating from high strain, high strain rate, and related adiabatic heating in a short timescale (<100 ns), the material characteristics of μPs are considerably altered locally within a single μP. However, since the actual CS is typically performed with a high feed rate, the essential parameters of colliding μPs, such as temperature, impact velocity, and size, are statistically estimated. Thus, CS-related materials studies have primarily relied on postmortem characterizations of CS specimens, and understanding the consolidation process of μPs has been slow compared to the technical progress in CS manufacturing. This chapter introduces emerging single-particle impact studies with precisely-controlled collision parameters, performed mainly based on the laser-induced projectile impact test (LIPIT). Unique aspects, representative demonstrations, opportunities, and perspectives of the single-particle studies are provided for fundamental advances of CS.