Electroless Nickel-phosphorous Coatings Research Articles

Wear and mechanical properties of electroless NiP and NiP-Silicon Carbide (SiC) composite coatings on En8 steel

Electroless coating technique is widely used in various industrial applications. This coating is the decision for some design applications with different actual attributes of electroless Nickel coatings, for example, hardness, wear resistance and coating thickness. The major advantages of Electroless Ni-P coatings are uniform coating thickness, improved wear and corrosion resistance, hardness, ability to deposit on surface activated non-conductors etc. In this article, a pure Nickel phosphorous (NiP) and Nickel phosphorous-Silicon Carbide (SiC) composite coatings are deposited on En8 steel using electroless coating to enhance the mechanical and wear properties of En8 steel. The wear test was carried out using Pin on Disc Tribometer against the counter part of stainless steel at atmospheric condition with various process parameters such as load, sliding velocity and sliding distance. The surface hardness and elemental composition of the coating were analyzed by Vickers hardness test and Optical Emission Spectroscopy respectively.

Mechanical properties and tribological behaviour of electroless Ni–P–Cu coatings on corrosion-resistant alloys under ultrahigh contact stress with sprayed nanoparticles

Threaded components manufactured from corrosion resistant alloys (CRA's) are vulnerable to galling. This paper develops a test matrix to systematically investigate the mechanical properties and tribological performance of electroless nickel phosphorous coatings on CRA's when subjected to high contact stress. Samples manufactured from 28Cr stainless steel were shot-peened for various periods prior to being electo/electroless coated. The coefficient of friction (CoF) of different coating systems was evaluated via sliding cross-pin method. Various wet and dry lubricants were utilised to examine tribological performance, furthermore the adhesion strength of the coatings was investigated by a bond and pull-off method. The study has shown a significant reduction in CoF for electroless nickel phosphorous coatings with prior shot-peening treatment and sprayed nanoparticles.

Monolayered versus multilayered electroless NiP coatings: Impact of the plating approach on the microstructure, mechanical and corrosion properties of the coatings

Electroless nickel-phosphorous (NiP) coatings were produced on low carbon steel substrates for a total plating time of 3 h. Different preparation modalities were pursued. Multilayered coatings were produced by stacking three layers of the same composition by successive electroless plating with rinsing steps in between. On the other hand, coatings termed ‘monolayered’ for the sake of comparison were deposited by one step electroless process, with and without undergoing bath replenishment of the electrolyte during plating. All the samples were subjected to thermal annealing at 400 °C for 1 h under argon atmosphere.The results show that the multilayer approach prevents crack propagation in the as-deposited coatings because the interfaces between layers block the advance of defects. Bath replenishment during monolayered coatings production creates pseudo-interfaces similar to those of the multilayered case but they are ineffective in terms of corrosion protection. Un-replenishment of the electrolyte promotes a change in the coating's microstructure from lamellar to columnar which severely worsens their performance. Upon annealing, the presence of interfaces, along with the recrystallization of the metallic matrix, promotes an upgrading of the corrosion performance of the multi-layered coatings. The corrosion products spread laterally at the interface where they stockpile. At a certain point, the accumulation of these by-products provokes the exfoliation of the outermost layer exposing the layer underneath to the corrosive media, thereby delaying the advancement of the corrosion attack. The results of this study highlight the importance of the plating approach selection, as well as the need for proper electrolyte maintenance during the production of high-performance electroless coatings.

Fabrication and investigation of the scratch and indentation behaviour of new generation Ni-P-nano-NiTi composite coating for oil and gas pipelines

Oil and gas pipelines operate under severe mechanical and chemical conditions, which could lead to catastrophic failure. Electroless nickel-phosphorous (Ni-P) coatings are an excellent candidate for protection against wear and corrosion for oil and gas pipelines. Ni-P coatings exhibit superior corrosion resistance over many commercially available coatings, as well as high hardness. However, electroless Ni-P coatings suffer from low toughness, which has limited its use in applications where high scratch and dent resistance is required. To enhance the toughness of the Ni-P coatings, nano-sized particles of superelastic NiTi alloy were incorporated within the coating. In the present work novel Ni-P-nano-NiTi composite coating has been successfully plated on API X100 pipe steel. Scratch tests under constant and increasing loads were performed to determine the effect of NiTi nano-particles on wear damages. Indentation tests were carried out to assess the dent resistance and crack modes of the coating. The addition of superelastic nano-particles into the Ni-P matrix led to toughening through transformation toughening, crack bridging, deflection, and microcracking. The composite coatings exhibited lower hardness in comparison to monolithic Ni-P coatings, but still provided considerable improvement upon the steel substrate. Optical and scanning electron examinations showed evidence of delamination, radial, and Hertzian cracking, as well as a reduction in crack length with the addition of superelastic NiTi.

Adhesivity of electroless Ni-P layer on austenitic stainless steel

Purpose: Optimization of testing of adhesivity of electroless deposited nickel-phosphorous coatings on austenitic stainless steel substrate. Design/methodology/approach: The main study has been focused on comparison of testing methods of adhesivity of electroless nickel- phosphorous coatings and analyses of influence of heat treatment on adhesivity of electroless nickel- phosphorous. Findings: It was found out that adhesivity of electroless nickel- phosphorous coatings can be successfully characterized by Vickers hardness tester. Research limitations/implications: The study was not extended to other types of deposited layers in order to be able to bring a general decision about applicability of this method in the testing of adhesivity of deposited layers. Practical implications: Based on experimental results it was found out that heat treated nickel-phosphorous coating have higher microhardness than non-heat treated electroless nickel-phosphorous coatings. High microhardness of heat treated nickel-phosphorous coating is connected with formation of Ni3P phase. Moreover, better adhesivity can be achieved by application of proper activation process before electroless coating. Originality/value: Standard Vickers hardness method was successfully applied in testing of adhesivity of electroless nickel- phosphorous coatings on austenitic stainless steel substrate.

Taguchi -Grey Based Optimization of Friction and Wear of Electroless Ni-P Coatings in Acidic Environment

The present study describes the synthesis of electroless Ni-P (nickel-phosphorous) coatings on mild steel substrate and optimization of the coating process parameters for minimum friction and wear in acidic (1M H2SO4) solution using Taguchi based grey relation analysis. The study is carried out using different combinations of four coating process parameters, namely, concentration of nickel source, concentration of reducing agent, deposition temperature and annealing temperature with three levels each. The tribological tests are conducted with a pin-on-disk tribometer. Analysis of variance reveals that annealing temperature has the maximum contribution in controlling the friction and wear characteristics of Ni-P coating. The coating is characterized using scanning electron microscopy, energy dispersive X-ray and XRD analysis, respectively. It is found that Ni-P coating is amorphous in as-deposited condition but gradually turns crystalline with heat treatment. Moreover the wear mechanism is found to be abrasive in nature.

Design, fabrication, and characterization of electroless Ni–P alloy films for micro heating devices

In this work electroless nickel–phosphorous coatings were used as the micro heaters for scanning thermal microscopy. The deposition of Ni–P alloys not only simplified the microelectromechanical system fabrication steps but also provided flexibility in the tuning of the resistance of the heating elements.Ni–P films were plated on patterned silicon substrates and silicon with a silicon nitride film. The pre-deposition reactive ion etch (RIE) treatment caused a change in surface roughness that enhanced the adhesion of Ni–P coatings. Optimization of RIE parameters and pH values could achieve selective deposition of Ni–P, thus helped the lift-off of a serpentine circuit pattern.The chemical composition and microstructure of Ni–P films affect the electrical properties of micro heaters. Energy-dispersive X-ray spectroscopy identified the Ni–P composition and confirmed its insignificant level of oxidation. The high-temperature X-ray diffraction indicated that the as-deposited film was crystalline Ni, which later transformed into Ni3P at higher temperature. The resistivity of Ni–P films was tailored between 10−5 and 10−7Ωm via a post-deposition annealing, which also obtained a stable temperature coefficient of resistance. Consequently, the performance of micro heaters could be designed with a high degree of flexibility.

Effect of Nanoadditives with Surfactant on the Surface Characteristics of Electroless Nickel Coating on Magnesium-Based Composites Reinforced with MWCNT

An experimental investigation has been carried out on optimizing process parameters of electroless nickel-phosphorous coatings on magnesium composite reinforced with carbon nanotube. A comprehensive experimental study of electroless Ni–P coatings on magnesium composite reinforced with multiwalled carbon nanotube under specific coating conditions was performed. The electroless coating bath consists of nickel sulphate (26 g/L), sodium hypo-phosphite (30 g/L) as reducing agent, sodium acetate (16 g/L) as stabilizer, and ammonium hydrogen difluoride (8 g/L) as the complexing agent. The surfactant SLS was added in the solution for better wetting and spreading of coating on substrate. The stabilizer thiourea (1 ppm) was added in the bath to prevent decomposition of bath. Different nanoadditives such as ZnO, Al2O3, SiO with various concentrations were used in the bath and their influence on coating process characteristics were studied The nano additives such as ZnO, Al2O3, SiO were added at concentrations of 0.1%, 0.5%, 1%, and 2% in the EN bath. The output parameters such as surface roughness, microhardness, specific wear rate, and surface morphology were measured. Surface morphology was studied using scanning electron microscope. The results showed that the proposed method resulted in significant improvement on the quality of the coatings produced.

Improving fretting fatigue behaviour of Al 7075-T6 bolted plates using electroless Ni–P coatings

In this paper, the effect of electroless nickel–phosphorous coatings on the fatigue and fretting fatigue behaviour of Al 7075-T6 bolted plates has been investigated. A double-lap bolted joint specimen was designed and manufactured from the aluminium plates and subsequently coated with Ni–P coatings of 40μm in thickness with a high phosphorous content of 10–13wt.%. Then, different tightening torques were applied to clamp the plates together with the aim of studying the effect of clamping force on the fretting fatigue life of the joints. Ni–P coatings were found to protect Al 7075-T6 clamped plates against fretting fatigue damages even at low fatigue loads where the uncoated joints showed a large reduction in their fatigue life due to the fretting effects. Fretting fatigue life of moderately and firmly clamped plates was successfully improved by approximately 30–40% and 50–60% respectively after the application of Ni–P coatings. Furthermore, fatigue cracks were found at the outer surface of the aluminium substrate at the edge of the hole associated with nodular defects whose deleterious effect was more pronounced at high cyclic loads. The Ni–P deposit presented a very good adhesion to the substrate at low and moderate loads; however, considerable delaminations and fracture of the coating film at high cyclic loads was observed.

Prediction of phosphorus content of electroless nickel–phosphorous coatings using artificial neural network modeling

A multilayer feedforward neural network with two hidden layers was designed and developed for prediction of the phosphorus content of electroless Ni–P coatings. The input parameters of the network were the pH, metal turnover, and loading of an electroless bath. The output parameter was the phosphorus content of the electroless Ni–P coatings. The temperature and molar rate of the bath were constant ( $$ 91^\circ {\text{C}},\:0.4\,{\text{Ni}}^{{{\text{ + + }}}} /{\text{H}}_{2} {\text{PO}}_{2}^{{ - - }} $$ ). The network was trained and tested using the data gathered from our own experiments. The goal of the study was to estimate the accuracy of this type of neural network in prediction of the phosphorus content. The study result shows that this type of network has high accuracy even when the number of hidden neurons is very low. Some comparison between the network’s predictions and own experimental data are given.