Experimental study of functionally graded materials of Fe/Al2O3 compound coatings on the steel substrate by using the laser ultrasound method

In this paper, the propagation characteristics of surface acoustic wave (SAW) and longitudinal wave in the iron-based alumina functionally graded materials (FGMs) were studied by using laser based ultrasonic technology, and then the ultrasound signals were analyzed to evaluate the properties of FGM. SAW and longitudinal wave were excited on FGM by using Nd:YAG pulsed laser and then detected by Polyvinylidene Fluoride (PVDF) transducer and laser interferometer, respectively. By analyzing the dispersion of SAW in the FGM the surface properties of materials were evaluated, and the internal nature and layered structures of FGM were determined by analyzing longitudinal wave and echo signals. The experimental results validate the correlation properties of FGM and demonstrate the feasibility and validity of the method by using SAW and longitudinal wave.