The present work deals with evaluation of corrosion behaviour of electrodeposited nanocrystalline Ni-W and Ni-Fe-W alloys. Corrosion behaviour of the coatings deposited on steel substrates was studied using polarization and electrochemical impedance spectroscopy techniques in 3.5% NaCl solution while their passivation behaviour was studied in 1N sulphuric acid solution. The corrosion resistance of Ni-W alloys increased with tungsten content up to 7.54 at.% and then decreased. In case of Ni-Fe-W alloys it increased with tungsten content up to 9.20 at.% and then decreased. The ternary alloy coatings exhibited poor corrosion resistance compared to binary alloy coatings due to preferential dissolution of iron from the matrix. Regardless of composition all the alloys exhibited passivation behaviour over a wide range of potentials due to the formation of tungsten rich film on the surface. © 2007 Elsevier B.V. All rights reserved.

S. Ganesh Sundara Raman

Department of Metallurgical and Materials Engineering

Suresh Krishnamoorthy Seshadri

Corrosion resistance

dissolution

Electrochemical impedance spectroscopy

Electrodeposition

Nanocrystalline alloys

Passivation

Polarization

NICKEL-IRON-TUNGSTEN ALLOYS

NICKEL-TUNGSTEN ALLOYS

Nickel alloys

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

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IIT Madras

Materials Science and Engineering A

Ni-W alloys with 16–28 at% tungsten (W) content were electrodeposited from citrate bath utilizing various pulse parameters. The influence of pulse parameters on microstructure, composition and mechanical properties was systematically studied. The corrosion behavior was analyzed in 1 M H2SO4 using potentiodynamic polarization and electrochemical impedance spectroscopy. Nanocrystalline Ni-W coatings were found to have superior corrosion resistance compared to their duplex nanocrystalline-amorphous counterpart. The corrosion behavior was rationalized based on semiconducting properties of oxide film using Mott–Schottky analysis and depth wise composition analysis utilizing X-ray Photoelectron Spectroscopy. An attempt is made to correlate corrosion current with intercrystalline defects. © 2019 Elsevier Ltd

Corrosion Science

Influence of pulse parameters on the mechanical properties and electrochemical corrosion behavior of electrodeposited Ni-W alloy coatings with high tungsten content

The present study deals with corrosion behaviour of compositionally modulated nanocrystalline Ni–W alloy coatings and conventional hard chrome coatings. Compositionally modulated Ni–W alloy coatings of known composition were systematically deposited using pulse current deposition. The corrosion behaviour was analysed using potentiodynamic polarization and impedance spectroscopy in 2N H2SO4. Compositionally modulated Ni–W alloy coatings depicted substantial improvement in corrosion resistance over its single-layer counterpart and hard chrome coatings. The corrosion behaviour was rationalized based on porosity and surface residual stresses present in these coatings. © 2019, © 2019 Institute of Materials, Minerals and Mining Published by Taylor &amp; Francis on behalf of the Institute.

Surface Engineering

Corrosion behaviour of compositionally modulated nanocrystalline Ni–W coatings

The aim of the present study is to understand the sliding wear response of pulse electrodeposited nanocrystalline nickel (Ni) – tungsten (W) alloy coatings in both as-deposited and heat-treated conditions. Ni-W alloy coatings with a wide range of W content (0% to 25 at%) were deposited using pulse electrodeposition and subsequently annealed at 700 °C up to 1 h. The tribological behaviour of Ni and Ni-W coatings (both as-deposited and heat-treated) was studied using a unidirectional pin-on-disc configuration at two different normal loads 3 kg and 5 kg respectively. All tests were performed in atmospheric air, at room temperature and at a constant sliding speed of 0.67 m s−1 using WC-Co disc as countersurface. Wear test results indicated that Ni-W alloy coatings exhibit greater wear resistance when compared to pure Ni coatings at both the loads. The wear mechanism in pure Ni coatings was attributed to severe abrasive wear along with brittle fracture whereas Ni-W alloy coatings exhibited mild ductile wear characterized by micro-ploughing. In the case of as-deposited Ni-W alloy coatings, the addition of W up to 17 at% increased the wear resistance due to improvement in hardness, however, further increase in W content resulted in amorphization and reduced the hardness with corresponding decrement in wear resistance. Heat treatment of coatings resulted in grain growth, crystallization of amorphous phase and precipitation of nanoprecipitates (beyond 12 at% W). Presence of nanoprecipitates and crystallization of amorphous phase resulted in significant improvement in wear resistance of the heat-treated coatings compared to their as-deposited counterparts. Addition of W to Ni did not vary the coefficient of friction (CoF) significantly and was found to be independent of W content, load and hardness of the coatings. The effect of load and hardness of the coatings on wear rate did not follow the wear relationship proposed by Archard. © 2018 Elsevier B.V.

Wear

Sliding wear of as-deposited and heat-treated nanocrystalline nickel-tungsten alloy coatings

The present study deals with the electrodeposition and structural characterization of as-deposited and heat treated nickel-tungsten (Ni-W) alloy coatings. The coatings were deposited using pulse reverse electrodeposition (PRED) and pulse electrodeposition (PED) from a Ni-W plating bath. Wide range of alloy compositions have been obtained with tungsten (W) percentage in the alloy ranging from 0% to 25&nbsp;at% by altering pulse parameters. The coatings were subsequently heat treated at a temperature of 700&nbsp;°C for 1&nbsp;h and were characterized in terms of phases present, grain size, hardness and elastic modulus. It was observed that the coatings were crystalline up to 12&nbsp;at% W and beyond which the coatings were found to be a mixture of amorphous and crystalline phases. Heat treatment resulted in crystallization of amorphous phase and precipitation of secondary phases. Substantial grain growth had occurred after heat treatment and as a result, the hardness of heat treated coatings was found to be less than that of their as-deposited counterparts up to 17&nbsp;at% W. Beyond 17&nbsp;at% W hardness of heat treated Ni-W was found to be higher due to dispersion hardening. © 2017 Elsevier B.V.

Surface and Coatings Technology

Influence of heat treatment on microstructure and mechanical properties of pulse electrodeposited Ni-W alloy coatings

Surface degradation processes such as wear, oxidation, corrosion and fatigue cause failure of many engineering components under varied circumstances. Among the various surface engineering processes, phosphate conversion coatings and, electro- and electroless plating processes have received widespread acceptance following their less complex processing sequence and cost-effectiveness. The present review addresses the recent developments in the areas of phosphate conversion coatings, electro deposition and electroless deposition. © 2011, by Walter de Gruyter GmbH & Co. All rights reserved.

Fulltext

Corrosion Reviews

Recent advances in surface treatment and electrodeposition

The present work deals with the effect of crystallite size on the hardness and fatigue life of steel samples coated with electrodeposited nanocrystalline Ni-W alloys. The Ni-W alloys were electrodeposited on steel samples at four different current densities (0.05, 0.10. 0.15 and 0.20 A/cm2) and at a temperature of 75 °C. The crystallite size of the deposit reduced (from 40 to 13 nm) with an increase in current density (from 0.05 to 0.20 A/cm2) due to an increase in the tungsten content (from 0.72 to 9.33 at.%). Ni-W alloy containing 9.33 at.% W and having a crystallite size of 13 nm exhibited the maximum hardness of 638 HV. The alloys, with the crystallite size in the range 40-13 nm, followed the direct Hall-Petch relation, i.e. hardness increased with a reduction in the crystallite size. The coated samples exhibited inferior fatigue lives compared to uncoated samples. This may be attributed to the presence of tensile residual stresses and inherent microcracks in the coatings. Among the specimens coated with Ni-W alloys, as the crystallite size decreased, the fatigue life of the specimen increased owing to the increase in hardness values. © 2006 Elsevier B.V. All rights reserved.

Materials Letters

Influence of crystallite size on the hardness and fatigue life of steel samples coated with electrodeposited nanocrystalline Ni-W alloys

The present work involves synthesis, characterization and evaluation of hardness and sliding wear resistance of electrodeposited nanocrystalline Ni-W alloys. Crystallite size reduced with an increase in current density due to an increase in the W content. Ni-W alloy with 9.33 at.% W plated at 75 °C exhibited the maximum hardness of 638 HV. Alloys plated at 75 °C followed direct Hall-Petch relation. However, alloys plated at 85 °C exhibited an inverse Hall-Petch relation below a crystallite size of 15 nm. Wear resistance of alloys plated at 75 °C increased due to an increase in hardness with a reduction in the crystallite size up to 20 nm. It reduced due to brittle fracture of the coating below 20 nm. Wear resistance of alloys plated at 85 °C increased with a reduction in the crystallite size in the direct Hall-Petch region and decreased in the inverse Hall-Petch region. Ni-W coatings with 6-8 at.% W exhibited superior wear resistance. © 2005 Elsevier B.V. All rights reserved.

Synthesis and evaluation of hardness and sliding wear resistance of electrodeposited nanocrystalline Ni-W alloys

Electroless Ni-P composite coatings have gained a good deal of popularity and acceptance in recent years as they provide considerable improvement of desirable qualities such as hardness, wear, abrasion resistance, etc. The disagreement among researchers on the corrosion behaviour of these coatings warrants a thorough investigation. Among the various techniques available for the determination of corrosion resistance, electrochemical impedance spectroscopy (EIS) is considered to be superior as it provides not only an assessment of the corrosion resistance of different deposits but also enables the mechanistic pathway by which the deposits become corroded to be determined. The present investigation focuses on the evaluation of the corrosion resistance of electroless Ni-P and Ni-P-Si3N4, Ni-P-CeO2 and Ni-P-TiO2 composite coatings produced using an acidic hypophosphite-reduced electroless nickel bath, using EIS. The study makes evident that the same fundamental reaction is occurring on all the coatings of the present study but over a different effective area in each case. The charge transfer resistance of electroless Ni-P and Ni-P composite deposits are in the range 32,253-90,700 Ω cm2, whereas the capacitances of these coatings are in the range 11-17 μF/cm2. The improved corrosion resistance obtained for electroless Ni-P and Ni-P composite coatings is due to the enrichment of phosphorus on the electrode surface, which enables the preferential hydrolysis of phosphorus over that of nickel. The better corrosion resistance obtained for electroless Ni-P composite coatings can be ascribed to the decrease in the effective metallic area prone to corrosion. Among the three electroless Ni-P composite coatings, the corrosion resistance is in the following order: Ni-P-CeO2 = Ni-P-Si3N4 &gt; Ni-P-TiO2.

Journal	Materials Science and Engineering A
ISSN	09215093
Open Access	No