Electroless Ni-P coating has been widely developed as a simple, low-cost and an easy technique [1]. In spite of the desirable properties of the binary Ni-P coatings such as high corrosion and wear resistance, good ductility and surface uniformity, improvement in their structure and corrosion protection has been studied by many scientists [2]. In the present research, for the first time, the specific effects of ultrasonic irradiation and its direction on the final morphology of coated layer and its anticorrosive performance have been reported. The resultant sonochemically electroless films on the mild steel have been also compared with the classical one which produced in the absence of ultrasound waves. The morphology of the final surfaces has been characterized and the chemical composition has been determined. The corrosion behavior for all samples has been studied by electrochemical techniques including the linear polarization resistance, Tafel extrapolation and electrochemical impedance spectroscopy. The results confirmed that the final characteristic of the fabricated surfaces was depended on two determining factors including the presence of ultrasonic waves during coating and the location of the plate with respect to the horn of ultrasonic apparatus. The analysis indicated that the Ni-P layer prepared by sonication has smoother surface with higher anticorrosive property in comparison with the classical one especially when the plate was situated in a perpendicular position with respect to the horn.

Keywords