Wear characteristics of mechanically milled TiO2 nanoparticles incorporated in electroless Ni–P coatings

Nanosized TiO₂ particles have been prepared by top down approach using mechanical milling with high energy planetary ball mill at 250 rpm for different extents of time (5, 10, 20, 30 and 40 h). Electroless (EL) Ni–P–TiO₂ nanocomposite coatings were developed using alkaline bath containing milled TiO₂ nanoparticles (4 g/l). The results show that, the morphology of TiO₂ particles milled for 40 h exhibit irregular shape with a particle diameter in the range of 33–45 nm. Wear studies of the coatings with 30 μm thickness were investigated using 1, 1.5 and 2 N loads with 0.1 and 0.2 m/s rotation speeds. The Ni–P–TiO₂ nanocomposite coatings exhibit the enhanced hardness and wear resistance as compared to that of Ni–P alloy coatings. Also the composite after heat treatment at 400 °C for 1 h in argon atmosphere showed improved hardness (1010 VHN) and wear resistance (1.5e-06 mm³/N m).     

Process and properties of electroless Ni–Cu–P–ZrO2 nanocomposite coatings

Electroless Ni–Cu–P–ZrO₂ composite coating was successfully obtained on low carbon steel matrix by electroless plating technique. Coatings with different compositions were obtained by varying copper as ternary metal and nano sized zirconium oxide particles so as to obtain elevated corrosion resistant Ni–P coating. Microstructure, crystal structure and composition of deposits were analyzed by SEM, EDX and XRD techniques. The corrosion behavior of the deposits was studied by anodic polarization, Tafel plots and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution. The ZrO₂ incorporated Ni–P coating showed higher corrosion resistance than plain Ni–P. The introduction of copper metal into Ni–P–ZrO₂ enhanced the protection ability against corrosion. The influence of copper metal and nanoparticles on microhardness of coatings was evaluated.     

Tribological characteristics of electroless Ni–B coating and optimization of coating parameters using Taguchi based grey relational analysis

Electroless nickel coating is an autocatalytic coating whose characteristics are very much dependent on the composition of electroless bath. The present study is an attempt to minimize the friction and wear characteristics of electroless Ni–B coatings simultaneously by optimizing the three coating parameters viz. bath temperature, concentration of reducing agent and concentration of nickel source together with the annealing temperature. Taguchi based grey relational analysis is employed for the optimization of this multiple response problem using an L₂₇ orthogonal array. Analysis of variance reveals that concentration of reducing agent has the maximum contribution in controlling the friction and wear behaviour of Ni–B coating. The interaction between bath temperature and nickel source concentration is also found to possess significant contribution in controlling the friction and wear characteristics. The surface morphology, composition and phase structure analysis are done with the help of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD), respectively. Moreover the wear mechanism is studied and found to be in general abrasive in nature.     

Antibacterial activity of electroless Ni–B coating

Abstract

A surface deposition treatment like electroless Ni–B deposition, which is a new candidate to use in a wide range of engineering applications owing to many advantages, including low cost and good wear resistance, may improve the antibacterial activity and physical properties of stainless steel biomedical devices. In the present study, the structural and antibacterial properties of electroless Ni–B coatings deposited on AISI 304 stainless steels under different deposition conditions were investigated. Escherichia coli, the most important causative organism for infection, were used as the testing bacteria for in vitro test, including incubation at 37°C and 24 h. X-ray diffraction for crystallographic examination and scanning electron microscopy for morphological analysis were also used. The characterisation results showed that the antibacterial activity of the steel substrates deposited with coatings having especially high NaBH₄ concentrations (1·2 g L^?1), thus being amorphous, was strongly improved. Furthermore, the bactericidal performance difference of the coatings exhibiting cauliflower-like surface morphology was more obvious than that of the others. Electroless Ni–B surface treatment may be utilised for increasing the lifetime of stainless biomedical devices.     

Using RSM optimization to fabricate Ni–Fe–P ternary alloy electroless coating and explore its corrosion properties

Journal of Materials Science: Materials in Electronics - In this paper, the Ni–Fe–P ternary alloy coating was fabricated by electroless deposition and the process parameters of coating...     

Pulse plating of Ni–B/WC nanocomposite coating and study of its corrosion and wear resistance

The aim of this study is to investigate the impact of WC content on the properties of the Ni–B/WC nanocomposites deposited by the pulse method. It is obtained that, although by addition of WC nanoparticles to the bath in initial steps (WC 4 and 8 g?l^?1), the grain size was increased and hence mechanical and electrochemical properties got worse, but at the higher amount of WC (WC 12 g?l^?1), due to the formation of the fine and packed structures, the great corrosion and wear resistance was achieved. The corrosion resistance of the Ni–B/WC12 g?l^?1 coating is 59,967?Ω and wear weight loss is 2.1 mg?cm^?2 with the friction coefficient of 0.64.     

Structure and morphology of electroless Ni–P deposits

Abstract

The high-voltage electron microscope has been used to study the structure and morphology of electroless Ni–P deposits of varying phosphorus contents. Except for low (<3 wt-%) phosphorus contents the deposits are amorphous. The crystallization processes depend on a number of variables, including thickness and phosphorus content of the deposit and presence or otherwise of an iron substrate. These processes include epitaxial crystallization of Ni_2.55P, spherulitic (or dendritic) crystallization of Ni_2.55P and Ni₃P, precipitation of nickel particles, and structures arising from interdiffusion between nickel, phosphorus, and the substrate.

MST/660     

Ternary alloy Ni–W–P nanoparticles electroless deposited within alumina nanopores

Abstract

A high yield of Ni–W–P nanoparticles with uniform size was prepared by electroless deposition within the nanopores of anodic aluminium oxide (AAO) template. The resulting Ni–W–P nanoparticles were amorphous and the Ni₃P phase was appeared in the sample annealed at 623 K. The crystallisation temperature of the nanoparticles is 579 K, which is 100 K lower than that of the Ni–W–P film. The nanoparticles possess a low coercivity at room temperature as the film, showing soft magnetic characteristics.     

Preparation and properties of electroless Ni–Zn–P alloy films

Electroless deposition of Ni–Zn–P layers was studied on steel electrodes by varying the bath temperature (40–90°C), pH and chemical composition. The deposition parameters were optimized. Alloys containing 70–86 wt % Ni, 6–20 wt % Zn and 6–10 wt % P are obtained at 20 m h^–1 and 85°C. Corrosion measurements were performed in aerated 5% sodium chloride solution, the corrosion potential and current density are, respectively, –0.49 V/SCE and 2.6 A cm^–2.     

An investigation on effects of heat treatment on corrosion properties of Ni–P electroless nano-coatings

Electroless Ni–P coatings are recognized for their excellent properties. In the present investigation electroless Ni–P nano-crystalline coatings were prepared. X-ray diffraction technique (XRD), scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were utilized to study prior and post-deposition vacuum heat treatment effects on corrosion resistance together with the physical properties of the applied coatings.     

High-temperature corrosion behavior of Ni–50Cr coating deposited by high velocity oxygen–fuel technique on low alloy ferritic steel

Ni–50Cr coatings were deposited using the HVOF technique on low alloy ferritic steel (2.25Cr–1Mo) substrates to improve their performance in high temperature steam environments. Different thermal spray parameters were studied in order to optimize the corrosion resistance of the coatings. High temperature thermal tests at 650 °C in different CO₂ atmospheres (air with 0, 15 and 25 vol.% CO₂) and thermal cycling tests in air at 550 °C and 650 °C were conducted to study the effectiveness of the coating protection system. The uncoated specimens were severely corroded but no oxidation in the coated substrates was detected. A reduction of 10 times in terms of weight change per area unit in the coated steel was obtained after 360 h of testing respect to that of the uncoated steel.     

Characterization and corrosion behavior of electroless Ni–P/nano-SiC coating inside the CO2 containing media in the presence of acetic acid

In this research, Ni–P and Ni–P/nano-SiC coatings were applied on the X70 steel substrate successfully without any surfactant. Then, CO₂ corrosion in the presence of acetic acid (HAc) was investigated using electrochemical techniques. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were used for surface analyses of the coatings. The electrochemical behavior of corrosion was investigated using polarization test and electrochemical impedance spectroscopy (EIS). XRD pattern of Ni–P/nano-SiC coating was very similar to that of Ni–P coating. EDS results demonstrated the presence of SiC particles in the coating. SEM images confirmed the presence of SiC nano-particles with almost uniform distribution in the coating. The corrosion current density was less in the Ni–P and Ni–P/nano-SiC coated samples than uncoated X70 steel. Ni–P/nano-SiC coated sample had the most corrosion resistance because of less effective metallic area available for corrosive media. The overall protection mechanism of Ni–P and Ni–P/nano-SiC coatings was achieved by formation of a layer of adsorbed hypophosphite anions (H₂PO₂⁻).     

Effects of conventional and active screen plasma nitriding on properties of electroless Ni–B coating

Abstract

In the present study, the properties of nitrided electroless Ni–B coatings prepared by conventional plasma nitriding and active screen plasma nitriding were investigated. For this purpose, electroless Ni–B coatings were deposited from an alkaline bath on AISI 4140 substrates. Then, some of the prepared coatings were plasma nitrided by conventional method and the other ones by active screen method under the same conditions. Microstructure, morphology, microhardness and wear resistance of the coatings were evaluated. Based on the results, post-treatments change the amorphous as deposited coating structure to a crystalline one, which increases microhardness and wear resistance. Employing plasma nitriding treatment on the coatings results in higher microhardness and superior wear resistance than conventional heat treatment. The sputtering of iron atoms during plasma nitriding process can be the main reason for these results. In addition, active screen plasma nitriding demonstrates less surface roughness and superior wear resistance than conventional plasma nitriding.     

Pulse electrodeposition and corrosion properties of Ni–Si3N4 nanocomposite coatings

The development of modern technology requires metallic materials with better surface properties. In the present investigation; Si₃N₄-reinforced nickel nanocomposite coatings were deposited on a mild steel substrate using pulse current electrodeposition process employing a nickel acetate bath. Surface morphology, composition, microstructure and crystal orientation of Ni and Ni–Si₃N₄ nanocomposite coatings were investigated by scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The effect of incorporation of Si₃N₄ particles in the Ni nanocomposite coating on the micro hardness, corrosion behaviour has been evaluated. Smooth composite deposits containing well-distributed silicon nitride particles were obtained and the crystal grains on the surface of Ni–Si₃N₄ composite coating are compact. The crystallite structure was face centred cubic (fcc) for electrodeposited nickel and Ni–Si₃N₄ nanocomposite coatings. The micro hardness of the composite coatings (720 HV) was higher than that of pure nickel (310 HV) due to dispersion-strengthening and matrix grain refining and increased with the increase of incorporated Si₃N₄ particle content. The corrosion potential (E _corr) in the case of Ni–Si₃N₄ nanocomposite had shown a negative shift, confirming the cathodic protective nature of the coating.     

Magnetic susceptibility of electroless Ni84P16 and Ni84P16–B4C

X-ray amorphous and crystallised NiP alloys possess structural inhomogeneities with nano-scale sizes, linked to the existence of a distribution of excess free volumes. The way the observed magnetic inhomogeneities are related to structural ones is not yet fully understood. In particular the dispersion of ceramic particles in a NiP-matrix composite adds further, uninvestigated structural peculiarities. In this work we focus our attention on the possibility of antiferromagnetic exchange between nickel atoms in the relevant materials. The magnetic susceptibility was investigated by the Faraday method in the temperature range 290–770 K with magnetic fields B=0.4–1.2 Tl. Amorphous pure-matrix and composite samples show one and two spin-glass transitions, respectively. Crystallised pure-matrix material shows field-independent susceptibility and ferromagnetic behaviour. Crystallised composites show field-dependent susceptibility, but are superparamagnetic.     

Preparation of polystyrene–clay nanocomposite by solution intercalation technique

Polymer–clay nanocomposites of commercial polystyrene (PS) and clay laponite were prepared via solution intercalation technique. Laponite was modified suitably with the well known cationic surfactant cetyltrimethyl ammonium bromide by ion-exchange reaction to render laponite miscible with hydrophobic PS. X-ray diffraction analysis in combination with scanning electron microscopy gives an idea of structural and morphological information of PS–laponite nanocomposite for different varying organo-laponite contents. Intercalation of PS chain occurs into the interlayer spacings of laponite for low organo-laponite concentration in the PS–O-laponite mixture. However, aggregation and agglomeration occur at higher clay concentration. The molecular bond vibrational profile of laponite as well as PS–laponite nanocomposite have been explored by Fourier transform infrared spectroscopy. Thermogravimetric analysis along with differential scanning calorimetry results reveal the enhancement of both thermal stability and glass transition temperature of PS due to the incorporation of clay platelets.     

Wear resistance of austenite–TiC–graphite microstructures prepared by laser coating

Abstract

Cast iron was laser coated with a nickel based covered electrode. The cover material consisted of titanium, cobalt, carbon, rare earth, and slag forming powders. The laser coated layer included substantial amounts of austenite, some TiC particles, and nodular graphite, as well as small quantities of austenite–Fe₃C eutectic. Sliding wear tests were carried out to evaluate the wear properties of the microstructures. The effects of alloying elements and microstructures on wear resistance were investigated. The role of austenite during wear was particularly emphasised by experimental tests.     

Insight of the interface of electroless Ni–P/SiC composite coating on aluminium alloy,LM24

Electroless nickel composite coatings with silicon carbide, SiC, as reinforcing particles deposited with Ni–P onto aluminium alloy, LM24, having zincating as under layer were subjected to heat treatment using air furnace. The changes at the interface were investigated using scanning electron microscope (SEM) and energy dispersive X-ray (EDX) to probe the chemistry changes upon heat treatment. Microhardness tester with various loads using both Knoop and Vickers indenters was used to study the load effect clubbed with the influence of second phase particles on the coating at the vicinity of the interface. It was observed that zinc was absent at the interface after elevated temperature heat treatment at 400–500 °C. Precipitation of copper and nickel with a distinct demarcation (copper rich belt) along the coating interface was seen with irregular thickness of the order of 1 μm. Migration of copper from the bulk aluminium alloy could have been the factor. Brittleness of the coating was confirmed on heat treatment when indented with Vickers. However, in composite coating the propagation of the microcrack was stopped by the embedded particles but the microcracks continue in the matrix when not interrupted by second phase particles (SiC).     

Microstructure and electromagnetic interference shielding effectiveness of electroless Ni–P plated polyester fabric

Microstructure and electromagnetic interference shielding effectiveness of electroless Ni–P deposits obtained from an alkaline hypophosphite reducing electroless nickel bath was studied. The effects of plating temperature on the deposition rate, surface morphology, chemical composition and structure of the electroless Ni–P deposits were investigated. Surface resistance and electromagnetic interference (EMI) shielding effectiveness (SE) of Ni–P plated polyester fabric were also evaluated. The results demonstrated electroless Ni–P plated polyester fabric present useful EMI shielding materials.