Comparison of corrosion resistance properties of Ni-P and Ni-W-P coatings obtained by electroless deposition

Issue 25(2) 2020
Pages 66-71

A.B. Drovosekov, Frumkin Institute of Physical Chemistry and Electrochemistry of RAS (IPCE RAS), Moscow, Russian Federation


Keywords: corrosion resistance properties, electroless coatings, Ni-P, Ni-W-P

http://www.doi.org/10.31615/j.corros.prot.2020.96.2-8

 

Corrosion resistance properties, such as porosity, stability in the atmosphere of NaCl mist, and anodic electrochemical activity in a sulfuric acid solution are studied and compared for Ni-W-P and Ni-P coatings obtained by electroless deposition. The studied coatings were obtained from solutions with glycine as the main ligand and contained 10.2 to 15.6 at.% of phosphorus and up to 3.3 at.% of tungsten. It is shown that Ni-W-P coatings with a tungsten content of 2.3 to 3.3 at.% and a thickness of 15 μm have a significantly lower porosity as compared with nickel-phosphorus coatings of the same thickness. Also, significantly better stability of Ni-W-P coatings in a NaCl mist atmosphere was observed, their corrosion damage degree is less than that of Ni-P coatings, and relatively little depends on the duration of exposure in a corrosive environment. Analysis of anodic polarization curves showed an almost similar electrochemical activity upon dissolution of Ni-P and Ni-W-P coatings in sulfuric acid. Both these types of electroless coatings showed a markedly better tendency to anodic dissolution than pure nickel. Taking into account the obtained experimental data, a conclusion is made as to the better protective characteristics of Ni-W-P coatings in comparison with nickel-phosphorus coatings. The main reason of the inferior protective properties of Ni-P coatings is their relatively high porosity.