Effect of ultrasonication and Na2MoO4 content on properties of electroless Ni-Mo-P coatings

摘要

Electroless Ni-Mo-P composite coatings with or without ultrasonic field were successfully deposited. The Sodium molybdate concentration was changeable to receive various Mo and P contents. Compared with the absence of ultrasound field, the coatings obtained smoother surface and higher Mo and P contents. The microhardness was determined by Vickers diamond indentation. The results showed that the hardness improved with increasing molybdenum and phosphorus content. The sample revealed the optimum hardness (886 HV) as it possesses 8 wt-% of Mo and 14 wt-% of P. Furthermore, the coatings exhibited higher hardness under ultrasound field. The corrosion resistance was analysed by potentiodynamic polarisation. The results showed that the corrosion resistance was enhanced in the increase of molybdenum. The sample with the highest Mo content (10 wt-%) showed the best corrosion resistance (5.81 mu A cm(-2)). In addition, the coatings with ultrasound field have an influence on improving the corrosion resistance of the coating.