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.

S. Ganesh Sundara Raman

Department of Metallurgical and Materials Engineering

Suresh Krishnamoorthy Seshadri

Brittle fracture

Characterization

Electrodeposition

Hardness

Nanostructured materials

Protective coatings

Synthesis (chemical)

Wear resistance

INVERSE HALL-PETCH

NANOCRYSTALLINE COATINGS

NICKEL TUNGSTEN ALLOYS

Sliding wear

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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It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

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 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 aims to study the hardness and wear resistance of electroless Ni-B coatings. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni-B coatings. The structure, microhardness and wear resistance of electroless Ni-B coatings, both in as-plated and heat-treated conditions, were evaluated using X-ray diffraction (XRD), Leitz microhardness tester and a pin-on-disc wear test apparatus. XRD patterns reveal that electroless Ni-B coatings are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. The microhardness of the electroless Ni-B coatings increases with increase in heat-treatment temperature and exhibit two maxima in the hardness vs. heat-treatment temperature curve. The specific wear rate increases with increase in applied load from 20 to 40 N and at all applied loads, the specific wear rate and coefficient of friction are less for heat-treated electroless Ni-B deposits compared to that obtained for as-plated ones. The wear process of electroless Ni-B coatings is governed by an adhesive wear mechanism. © 2004 Elsevier B.V. All rights reserved.

Electroless Ni-B coatings: Preparation and evaluation of hardness and wear resistance

The present work deals with the formation of Ni-P/Ni-B duplex coatings by electroless plating process and evaluation of their hardness, wear resistance and corrosion resistance. The Ni-P/Ni-B duplex coatings were prepared using dual baths (acidic hypophosphite- and alkaline borohydride-reduced electroless nickel baths) with both Ni-P and Ni-B as inner layers and with varying single layer thickness. Scanning electron microscopy (SEM) was used to assess the duplex interface. The microhardness, wear resistance and corrosion resistance of electroless nickel duplex coatings were compared with electroless Ni-P and Ni-B coatings of similar thickness. The study reveals that the Ni-P and Ni-B coatings are amorphous in their as-plated condition and upon heat-treatment at 450 °C for 1h, both Ni-P and Ni-B coatings crystallize and produce nickel, nickel phosphide and nickel borides in the respective coatings. All the three phases are formed when Ni-P/Ni-B and Ni-B/Ni-P duplex coatings are heat-treated at 450 °C for 1h. The duplex coatings are uniform and the compatibility between the layers is good. The microhardness, wear resistance and corrosion resistance of the duplex coating is higher than Ni-P and Ni-B coatings of similar thickness. Among the two types of duplex coatings studied, hardness and wear resistance is higher for coatings having Ni-B coating as the outer layer whereas better corrosion resistance is offered by coatings having Ni-P coating as the outer layer. © 2003 Elsevier B.V. All rights reserved.

Materials Chemistry and Physics

Electroless Ni-P/Ni-B duplex coatings: Preparation and evaluation of microhardness, wear and corrosion resistance

Nickel composite coatings have been prepared on mild steel substrates by sediment electro-co-deposition (SECD) technique. Silicon nitride, fly ash and calcium fluoride are used as the reinforcements. Metallographic studies, microhardness, friction and wear tests under various loads and sliding speeds have been carried out on these coatings. Optical and scanning electron microscopy (SEM) studies on the worn surfaces were conducted. A theoretical model was used to predict the wear rates of the composite coatings. All the composite coatings exhibited a lower coefficient of friction and better wear resistance when compared with nickel coatings at all loads and sliding velocities studied. However, nickel-calcium fluoride composite coatings possessed the lowest coefficient of friction and wear rates. Significant effect of load and sliding speed on both the coefficient of friction and wear rates of nickel, nickel-silicon nitride and nickel-fly ash coatings has been observed. SEM studies of the worn surfaces reveal delamination process at higher loads. The predicted wear rates are in reasonable agreement with the experimental values. © 2003 Elsevier Science B.V. All rights reserved.

Journal	Materials Science and Engineering A
ISSN	09215093
Open Access	No