To fully understand particle interactions with both substrate and neighboring particles in cold spray, ultrasound wave generation and ultrasonic monitoring of particle impacts were studied. The multi–channel ultrasonic system works in pulse– echo and passive modes. In pauses between pulse–echo data acquisition frames the system is in the passive mode receiving the signals generated by the particle impacts. The particles being deposited generate the ultrasonic signals in a very wideband frequency range at more than 40 dB signal-to-noise ratio. The particle impact signals are considered as a sum of the background wideband noise and the sparse strong pulses observed when the nozzle passes over the location of the transducer. It was shown that these components of the particle impact signal can be separated by threshold processing. The results of the passive monitoring are confirmed by the ultrasonic pulse–echo and direct measurements of a deposited coating geometry.

This study evaluates a nondestructive method for determining the adhesion strength and porosity of thermally sprayed coatings. The method is based on ultrasonic surface echo measurements. Porosity is surmised by the impedance of the coating and adhesion by the transmission coefficient. Experimental results confirmed that the method is effective for its intended use.