Material characterization of thermal sprayed nickel aluminum coatings using a laser ultrasound technique

Thermal spraying processing usually use nickel-aluminum alloy system as major powder due to its strong adhesion to substrates. The contents of powder material and the processing parameters used in the spraying process cause material properties of coating exhibiting a wide variation. It is difficult to investigate mechanical properties of coating layer in nondestructive way. This research aims at nondestructive characterization of thermal spraying coatings. A laser-generation/laser-detection laser ultrasound technique (LUT) is used for the measurements of dispersion spectra of guided waves. Theoretical model for surface waves propagating along a multilayered structure with coating and substrate is used to model the sprayed coatings. An inversion algorithm based on Shuffled Complex Evolution (SCE-UA) is used to extract mechanical properties from the measured dispersion spectra cooperating with theoretical model. In the results, three sets of surface wave dispersion spectra are measured for three different thickness coatings. The difference thickness of coatings is reacted to dispersion spectrum of guided waves. This method is potentially useful to characterize the mechanical properties of thermal spraying coating in a nondestructive way.