Interfacial bonding and microstructural evolution of Al in kinetic spraying

Bonding and microstructural evolution of Al particles in kinetic spraying (cold gas dynamic spraying) result from ultra-high strain rate plastic deformation during supersonic single and successive collisions of the particles. The coating formation of kinetic spraying is composed of three stages (an individual particle impact + subsequent impacts + isothermal heating during full coating). When a single particle impacts, interfacial shear strain location under adiabatic state produces inter-particle bonding and grain refinement at narrow zone (<220 nm) by continuous dynamic recrystallization. After the individual particle impact, successive supersonic in-flight particle impact results in static recovery and static recrystallization at unrefined area using the heat energy converted from the kinetic energy as activation energy. In this study, the bonding state and microstructure of individually impacted Al particle and full Al coating were analyzed using a focused ion beam technique and a transmission electron microscopy. The mechanisms of interfacial bonding and microstructural evolution of Al particle during kinetic spraying were suggested.