Ultrasonic phosphating of Nd-Fe-B magnetic alloys

Ultrasonic phosphating of ground surfaces of Nd-Fe-B magnets was performed at two ultrasound intensities. The process was shown to follow the relationships known for topochemical reactions. High-frequency processing is more efficient in suppressing the autoinhibiting adsorption of reaction intermediates promoted by Schlichting’s acoustic winds in the initial stages of phosphating and has a stronger accelerating effect on intergranular diffusion in the later stages. The low-frequency cavitation results in the erosion of the growing coating. The acceleration of solid-state diffusion prevails over the effect of cavitation heating. The high-frequency phosphating of Nd-Fe-B magnets is more attractive from the viewpoint of the growth rate and corrosion resistance of the resultant coatings.