Deposition behavior of electroless Ni-W-P coating on Zr-4 surface

Electroless Ni-W-P coating was successfully deposited on Zr-4 alloy by an electroless plating technique. In order to obtain the deposition behavior of Ni-W-P coating on the Zr-4 surface, scanning electron microscopy (SEM, ZEISS EV0MA15), energy dispersive X-ray spectrometer (EDS), X-ray diffractogram (XRD, DX-2700) and electrochemical workstation were used to observe the changes of microstructure, elemental composition, phase composition and corrosion resistance of the coating at different times (3, 5, 10, 30, 60, and 120 min). Based on the analysis of test results, the growth process of Ni-W-P coating on a pre-coated Zr-4 surface can be summarized as follows: Na3ZrF7?Na3ZrF7 partially transformed into NiZrP & RARR;NiZrP was covered by the amorphous materials composing of Ni, W and P elements. Moreover, incomplete Ni-W-P coating did not have the ability to improve the corrosion resistance of the Zr-4 substrate, and the nickel unit cell grew for at least 30 min before initially forming a barrier to the corrosive medium.