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Spasojevic M.,University of Kragujevac | Ribic-Zelenovic L.,University of Kragujevac | Maricic A.,Joint Laboratory for Advanced Materials of SASA | Spasojevic P.,University of Belgrade
Powder Technology | Year: 2014

A dark gray nanostructured coating of an alloy composed of 87.3wt.% Ni, 11.3wt.% Fe and 1.4wt.% W (Ni87.3Fe11.3W1.4) was electrodeposited from an ammonia citrate bath on a titanium cathode at a current density of 500mAcm-2.A cathodic polarization curve was recorded and dependence of the current efficiency of alloy deposition on current density was determined. Partial polarization curves for alloy deposition and hydrogen evolution were also measured. Alloy deposition at current densities of up to 300mAcm-2 is an activation-controlled process which turns into a diffusion-controlled process at higher current densities. At potentials more positive than -960mV, hydrogen is evolved from NH4 + and (HCit)3- ions (where (HCit)3- denotes triply deprotonated citric acid, C6H5O7 3-). At potentials more negative than -960mV, hydrogen evolution from water is the dominating reaction.SEM images show that the surface of the deposit obtained at 500mAcm-2 has a globular structure containing a large number of craters, mostly located between the globules.XRD analysis revealed that the alloy contains an amorphous matrix with embedded nanocrystals of the FCC-structured solid solution of Fe and W in Ni with a mean particle size of 8.8. nm. The deposit has a high internal microstrain value and a high density of chaotically distributed dislocations.Heating and milling the alloy cause structural changes involving changes in the magnetic properties of the alloy. Structural relaxation takes place in the temperature interval of 80. °C tO 420. °C. In this temperature range, magnetization of both as-deposited and milled alloy samples increases with increasing temperature, reaching maximum at a certain temperature, but decreases thereafter with further heating. During structural relaxation, short-term structural arrangement facilitates the expansion and orientation of magnetic domains, leading to increased magnetization of the alloy. The abrupt decline in magnetization at higher temperatures is the result of a heat-induced change in magnetic domain orientation.Annealing the alloy at temperatures above 420. °C causes amorphous phase crystallization and growth of crystal grains of the FCC-structured solid solution of Fe and W in Ni, as well as a simultaneous decrease in internal microstrain and mean density of chaotically distributed dislocations. The same structural changes, somewhat lower in intensity, are also caused by alloy milling. The new state of the microstructure achieved through annealing and milling is best illustrated by the mean crystal size. The increase in mean crystal size results in a shift of the Curie temperature towards lower temperatures, whereas magnetization increases at first, reaching maximum at a certain mean crystal size, but decreases, thereafter, with a further increase in mean crystal size. © 2014.

Pesic O.,Joint Laboratory for Advanced Materials of SASA | Spasojevic M.,Joint Laboratory for Advanced Materials of SASA | Spasojevic M.,University of Kragujevac | Jordovic B.,Joint Laboratory for Advanced Materials of SASA | And 3 more authors.
Science of Sintering | Year: 2014

Nanostructured nickel-cobalt-molybdenum alloy powders were electrodeposited from an ammonium sulfate bath. The powders mostly consist of an amorphous phase and a very small amount of nanocrystals with an mean size of less than 3 nm. An increase in deposition current density increases the amorphous phase percentage, the density of chaotically distributed dislocations and internal microstrains in the powders, while decreasing the mean nanocrystal size. The temperature range over which the structural relaxation of the powders deposited at higher current densities occurs is shifted towards lower temperatures. A change in relative magnetic permeability during structural relaxation is higher in powders deposited at higher current densities. Powder crystallization takes place at temperatures above 700oC. The formation of the stable crystal structure causes a decrease in relative magnetic permeability.

Spasojevic M.,University of Kragujevac | Spasojevic M.,Joint Laboratory for Advanced Materials of SASA | Cirovic N.,Joint Laboratory for Advanced Materials of SASA | Ribic-Zelenovic L.,University of Kragujevac | And 4 more authors.
Journal of the Electrochemical Society | Year: 2014

Nanostructured nickel-iron-tungsten alloy coatings were electrodeposited from an ammonia citrate bath on steel and copper substrates at current densities in the range of 50 to 300 mA cm-2. The contents of iron and tungsten in the alloy increase and that of nickel decreases with increasing deposition current density. At current densities below 100 mA cm-2, smooth shiny coatings with no cracks and craters are deposited. Higher current densities result in matte coatings developing cracks and craters. XRD analysis showed that the coatings contain nanocrystals of FCC structured solid solution of iron and tungsten in nickel embedded in an amorphous matrix. Increasing deposition current density leads to an increase in the amorphous phase content and a decrease in both the content and mean crystallite size of the FCC phase. The coatings with an increased amorphous phase content and a decreased mean FCC crystallite size exhibit lower magnetization and reduced hardness. During annealing at temperatures up to 400°C, the alloy undergoes structural relaxation along with short-range structural arrangement, resulting in increased magnetization and hardness. At temperatures above 500°C, annealing leads to amorphous phase crystallization and crystal grain growth in the FCC solid solution, thus leading to reduction in both magnetization and hardness. © 2014 The Electrochemical Society. All rights reserved.

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