Ultrasonic Evaluation of the Adhesion Between Regenerative Coatings and Steel Substrates

The rise in resource consumption and environmental pressures are driving the development of a circular economy, in which the remanufacturing of machine and vehicle parts plays a significant role. Despite numerous studies on regeneration technologies (including additive manufacturing, cladding, and spraying), the literature lacks analyses concerning the non-destructive evaluation of the coating–substrate bond quality—when tested from the substrate side. The aim of this study was to evaluate the applicability of the ultrasonic method for the detection of defects (delaminations, detachments) in the adhesive joint between the regenerative coating and the base material. The study demonstrated that the ultrasonic method enables non-destructive, portable, and single-sided inspection of the integrity of the coating–substrate interface, making it a useful tool in industrial practice. Fifteen samples (including one reference sample) of varying thicknesses (from 1.9 µm to 1753.9 µm) were tested using ultrasonic probes with frequencies ranging from 1 MHz to 20 MHz. It was found that the adhesion of coatings approximately 74 µm thick can be estimated using an ultrasonic wave with a frequency of 1.66 MHz, whereas for coatings approximately 250 µm thick, adhesion can be estimated using higher frequencies, i.e., from 2.75 to 20 MHz.