Corrosion Resistance Of Electroless Ni-P/Cu/Ni-P Multilayer Coatings

Abstract

coatings were prepared by deposition of Cu layer between two Ni-P layers. The Cu layer was deposited by metal displacement reaction between Cu 2+ and Fe atoms. Corrosion behavior of single-layer Ni-P coatings, double-layer Ni-P/Cu coatings, and three-layer Ni-P/Cu/Ni-P coatings were investigated by electrochemical tests in 3.5% NaCl solution. The three-layer coatings exhibited more positive E corr and decreased I corr compared with conventional single-layer Ni-P coatings, which indicated an improved corrosion resistance. The polarization curves of the three-layer coatings were characterized by two passive regions. The improved corrosion resistance was not only attributed to the function of the blocked pores of Cu. The Cu interlayer also acted as a sacrificial layer instead of a barrier in the coatings, which altered the corrosion mechanism and further improved the corrosion resistance of the coatings.Keywords: electroless plating, multilayer coatings, porosity, electrochemical tests, crystalline Cu layerWielowarstwowe powłoki Ni-P/Cu/Ni-P wytworzono metodą osadzania miedzi pomiędzy dwoma warstwami Ni-P. Warstwę Cu otrzymano dzięki reakcji wypierania metalu przez metal (dla miedzi i żelaza). Aby określić właściwości korozyjne jednowarstwowej powłoki Ni-P, dwuwarstwowej Ni-P/Cu oraz trójwarstwowej Ni-P/Cu/Ni-P przeprowadzono pomiary elektrochemiczne w 3,5% roztworze NaCl. Powłoki trójwarstwowe w porównaniu do jednowarstwowych wykazały się większą wartością E corr , przy malejącej wartości I corr . Wskazuje to na poprawę odporności na korozję. Krzywe polaryzacji dla powłok trójwarstwowych charakteryzują się występowaniem dwóch obszarów pasywacji. Poprawa odporności na korozję jest skutkiem nie tylko tzw. zjawiska blokowania porów w miedzi. Powłoka z Cu działała także jako warstwa protektorowa, modyfikując mechanizm korozji i poprawiając odporność korozyjną powłok.

Damage Development on the Surface of Nickel Coating in the Initial Period of Erosion

“…Thus, literature studies have shown that Ni–P coatings, regardless of the P content, are characterized by a better corrosion resistance (a lower corrosion rate) compared to steels. The corrosion tests presented in this paper are in accordance with the results obtained in [ 48 , 49 , 50 , 51 , 52 ] and confirm the better corrosion resistance of the Ni–P coating comparing to the Nimax substrate steel, regardless of the immersion time.…”

“…Investigations of the electroless Ni–P coatings presented in [ 48 , 49 , 50 ] showed that the content of phosphorus affects porosity and corrosion resistance. The content of phosphorus depends on many parameters, such as concentration of the phosphorus donor in the bath, pH, temperature, or current density.…”

“…In addition, defects with a wide range of diameters were formed during coating deposition. According to [ 49 ], defects in electroless Ni coatings are related to the phosphorus content and coating thickness. Thus, the cause of the numerous and large defects was likely the high content of phosphorus.…”

Recent advances in electroless-plated Ni-P and its composites for erosion and corrosion applications: a review

“…Multilayers of electroless ENP coatings were prepared by Zhao et al [56] and were arranged in the following configuration: Ni-P/Cu/Ni-P. The presence of crystalline Cu deposits blocks pores of the three-layer coatings, leading to a decrease in coating porosity and to an increase in corrosion resistance.…”

“…The coated samples and their times of deposition are described as the follows: sample 6 (Ni-P single layer, 60 min), sample 7 (Ni-P inner layer, 10 min/Cu interlayer, 10 min/Ni-P outer layer, 50 min), sample 8 (Ni-P inner layer, 20 min/Cu interlayer, 10 min/ Ni-P outer layer, 40 min), sample 9 (Ni-P inner layer, Fig. 6 Porosities of the single-(sample 6) and three-layer coatings (Ni-P/Cu/Ni-P), samples 7-11, for different deposition times [56] 30 min/Cu interlayer, 10 min/Ni-P outer layer, 30 min), sample 10 (Ni-P inner layer, 40 min/Cu interlayer, 10 min/Ni-P outer layer, 20 min), and sample 11 (Ni-P inner layer, 50 min/Cu interlayer, 10 min/Ni-P outer layer, 10 min). Sadreddini et al used SiO 2 nanoparticles to form electroless Ni-P-SiO 2 nanocomposite coatings on Mg substrate that enhanced the porosity of the ENP coatings [57].…”