Magnetostriction of Fe-Ga coatings and their application in ultrasonic guided wave sensing

Fe₈₃Ga₁₇ (at. %) coatings with a thickness of 270-500 μm were prepared on 316L stainless steel by high velocity oxy-fuel spraying technology. The coatings exhibited a lamellar structure, and the magnetostriction reached 34.5 ppm. The magnetostrictive coatings were applied to electromagnetic acoustic transducers (EMATs), where the different bias magnetic fields and coating thicknesses were considered to examine the ultrasonic guided wave sensing capability and the detection sensitivity. The 180-kHz ultrasonic guided waves were captured from artificial defects and the pipe end under different bias magnetic fields. Among them, the EMATs exhibited the best sensing performance under a bias magnetic field of 255.7 Oe. Meanwhile, magnetostrictive stress induced the decrease of the magnetic permeability and the rearranged magnetic moment, resulting in a large strain sensitivity (dλ/dH). Because of the relatively good field sensitivities in magnetization and magnetostriction, the EMATs using Fe₈₃Ga₁₇ coating with a thickness of 500 μm exhibited better detection sensitivity than that of 300 μm. This work provides a good prospect of Fe-Ga alloy coatings applied in non-destructive testing.