5. Deposition mechanisms

Cold spray leads to deposition if and only if the sprayed particles can adhere to the substrate and to each other as they accumulate with densification. This condition led, shortly after the advent of the process, to the definition of the notion of critical speed. This reflects the impact behavior of the sprayed particle, with its mechanical part via plastic deformation, and its metallurgical part via metallurgical transformations at the particle-substrate interface. The word substrate is taken in its general sense and can therefore represent, for example, a particle that has already been deposited. Improving particle impact behavior to meet critical velocity conditions requires mechanical and/or metallurgical modifications to the material system at impact. Studying these modifications is tantamount to assessing the "impact of impacts". The main ones will be described when we review the...