ABSTRACT
Cold spray (CS) is a process whereby metallic particles are consolidated to form a coating by means of ballistic impingement upon a suitable substrate. The particles typically ranging in size from 5 to 100 μm are accelerated to high velocity by injection into a stream of high-pressure gas that is subsequently expanded to supersonic velocity through a nozzle. After exiting the nozzle, the particles are impacted onto a substrate, where the solid particles deform and create a bond with the substrate. As the process continues, particles continue to impact and form bonds with the previously consolidated material. The properly established process produces a uniform deposit with a very little porosity and high bond strength. However, because of the complexity of the particle consolidation phenomena and difficulties for controlling all parameters of the spray process various defects may arise in the coatings. Thus, nondestructive evaluation of the coatings and monitoring of the CS process are important problems. This chapter is devoted to application of ultrasonic testing and characterization of the coating deposited by CS technology and ultrasonic in-line monitoring in pulse-echo and passive modes.
