Sonochemical Formation of Intermetallic Coatings

An energy-dispersive X-ray (EDX) study of the agglomerates produced during the sonication of a series of mixed-metal powders in decane indicates that metal particles are both fused by the action of ultrasound and develop coatings which are intermetallic in nature. The principal mechanism of these effects is believed to be interparticle collision caused by the rapid movement of particles of less than 50 μm diameter which are propelled by shockwaves generated at cavitation sites. By examination of mixed-metal systems including Ni/Co, Al/Ni, Al/Co, Ni/Mg, and Cu/Mo with substantially different tribological characteristics, it has been determined that the coatings are generated by both adhesive wear and direct impact. The fusion of Cu and Mo is particularly intriguing, as these two metals are immiscible below 1000 °C. This indicates the enormous impact temperatures produced in sonically induced collisions. The mechanisms of intermetallic coatings produced via ultrasound are discussed.