Electroless Ni-P/nano-WO3 coating and its mechanical and corrosion protection properties

Abstract

Tungsten trioxide (WO3) nanoparticles were loaded into the electroless Ni-P bath in order to synthesize the Ni-P/nano-WO3 coatings. Scanning Electron Microscopy (SEM) showed that pore-free, compact, and columnar Ni-P/nano-WO3 coatings without inter-columnar corrosion defects were applied on the brass substrate by the addition of 0.1, 0.3, and 0.5 g. L−1 WO3 nanopowders into the plating bath. The co-deposition of the WO3 nanoparticles was verified by Energy Dispersive X-ray Spectroscopy (EDS) technique. Moreover, uniform distribution of the imbedded nanoparticles was shown by the EDS mapping. Diffraction peaks of the nanoparticles were not observed in X-ray Diffraction (XRD) pattern of the Ni-P/nano-WO3 coatings, which may be due to homogenous distribution of the nanoparticles. Electrochemical Impedance Spectroscopy (EIS) and pH measurements in the plating bath revealed that electrostatic attraction acts as an effective factor to trap the nanoparticles in the matrix of the Ni-P/nano-WO3 coatings. The anti-corrosion characteristic of the Ni-P deposit in 3.5 wt% NaCl corrosive electrolyte was significantly improved by co-deposition of the WO3 nanoparticles. The Ni-P/nano-WO3 coating which was obtained by loading 0.3 g. L−1 nanoparticles showed the highest corrosion resistance. Furthermore, micro-hardness and wear resistance of the electroless layer were significantly enhanced after incorporation of the WO3 nanoparticles.