Effect of pH on the characteristics of electroless Ni-P coatings

Abstract

In this study electroless NiP coatings were deposited on W302 steel substrates. The effects of bath pH and heat treatment at 400 °C were investigated on the surface morphology, phase structure, phosphorus content, thickness and microhardness of the coatings. It was observed that both the phosphorus content and coating thickness are dependent on the bath pH. In an acidic/neutral bath, low and medium phosphorus coatings with thickness of 13.9-19.8 μm were synthesized, while in an alkaline bath, high phosphorus, 4.8-5.8 μm-thick coatings were formed. Coatings containing medium or high P seemed to be amorphous, while low P coatings had microcrystalline structures. Hardness was also dependent on the composition of the coating. After heat treatment, the structure of the coatings transformed into crystalline Ni with the precipitation of Ni 3 P phases, which resulted further increases in hardness.

Improvement of AZ91 Alloy Corrosion Properties by Duplex NI-P Coating Deposition

“…In their study, the low-phosphorus Ni-P coatings (2-3 wt.% of P) reached the hardness of 700 HV, and the high-phosphorus Ni-P coatings (10-12 wt.% of P) reached the hardness of 510 HV. In agreement with their observations, also in the work of Czagany and Baumli [29], the microhardness of the coatings decreased with increasing phosphorus content. As the authors stated, the highest microhardness (634 HV0.01) was reached for the coating containing 3.67 wt.% of P while the lowest microhardness (363 HV0.01) was reached for the coating with 13.48 wt.% of P. Figure 4 shows typical potentiodynamic curves of AZ91 magnesium alloy and deposited Ni-P coatings on AZ91 alloy in 0.1 M NaCl.…”

Preparation of Sol-Enhanced Ni–P–Al2O3 Nanocomposite Coating by Electrodeposition

“…Similar situations have been reported in a similar pH bath [24,25]. Besides, it has been pointed out that the pH of the plating solution has an effect on the P content of the coating, that is, the hardness of the coating increases with the decrease of P content [26]. The increase of pH may decrease the P content in the coating.…”

Recent advances in electroless nickel‑boron coatings

“…As said in the introduction, electroless deposition of nickel leads to different types of coatings depending on the reducing agent [15][16][17], and electroless nickel-phosphorus (EN-P) is the most popular [18,162,[201][202][203][204]. Both types of coatings are, however, considered as alternatives to hard chrome plating [18,19].…”

“…The chemical composition of electroless nickel coatings, which is mostly represented by the content of boron or phosphorus, significantly affects the properties of the deposit [20,146,205,206]. This chemistry is in turn influenced by the bath formulation and operating conditions as seen previously [16,22,112,146].…”