1. Fundamentals of Cold Spray Processing: Evolution and Future Perspectives

Cold gas dynamic spraying, or cold spraying (CS), is a solid-state coating process wherein powders in a carrier gas are accelerated toward a substrate. Under sufficiently high impact velocities, the powder particles deform plastically and adhere to the substrate. Metals, ceramics, polymers, and composites can be deposited using CS. Among currently available surface coating technologies, CS offers several advantages over thermal spraying, because it utilizes kinetic rather than thermal energy for deposition. This avoids residual stresses, oxidation, and undesirable chemical reactions. The intent to develop new material systems with enhanced properties that fulfill the required surface and interface functionalities for components with many applications has inspired CS investigations of many material combinations. The number of studies and patents on CS and CS-related technologies has increased exponentially in recent years, establishing much new information in a short time. In this chapter, the process of CS is discussed from mechanistic and technological perspectives, including its general operating parameters, current applications to specific material systems, and ongoing research increasing the scope of the technique. A critical discussion on developing CS technologies examines the microstructural bonding mechanisms utilized in variations on the process. Future investigations are suggested, particularly in quantitatively linking CS processing parameters to the behaviors of material systems during impact. This chapter briefly summarizes the rapidly expanding common knowledge on CS to assist researchers and engineers in future endeavors with this technology.