Effect of Microstructural Changes during Annealing on Thermoelectromotive Force and Resistivity of Electrodeposited Ni_85.8Fe_10.6W_1.4Cu_2.2 Alloy

Abstract

Cu 2.2 alloy powder containing nanocrystals of an FCC-structured solid solution of iron, tungsten, and copper in nickel embedded in an amorphous matrix was electrodeposited from an ammonia citrate solution. The alloy exhibits thermal stability in the temperature range between 25 ∘ C and 150 ∘ C. Over the range 150−360 ∘ C, the alloy undergoes intense structural relaxation which considerably increases the electron density of states and, hence, its electrical conductivity. Less intense structural relaxation takes place at temperatures between 360 ∘ C and 420 ∘ C. In the temperature range of 420 ∘ C to 460 ∘ C, relatively more intense changes in the electron density of states at the Fermi level occur, as induced by the structural relaxation resulting from the stabilization of larger less mobile tungsten atoms and copper atoms. The large decrease in electrical resistivity and the high increase in the electron density of states at the Fermi level in the temperature range 460−520 ∘ C are due to amorphous matrix crystallization and FCC-phase crystal grain growth.

Electrodeposition, Microstructure and Magnetic Properties of Nickel-Cobalt-Copper Alloy Powders

“…Specifically, during the alloy deposition, copper is co-deposited at the limiting diffusion current at high overpotential, which leads to the rapid formation of nuclei and generation of deposits having large surface areas. 50,59,60 The current efficiencies of alloy deposition decrease with increasing current density. At the same current density, the current efficiencies of the copper-containing alloy are higher by about 12% than those of the alloy without copper.…”

“…The greater density of nuclei on the deposit surface causes the formation of smaller crystalline grains, which exhibit higher internal microstrain values and a higher density of chaotically distributed dislocations. 49,50,59,60 As the mean nanocrystal size decreases, the mass percentage of the amorphous matrix located between the nanocrystals increases. [61][62][63][64] Therefore, Ni/Co electrodeposits with Cu have a larger amount of the amorphous phase compared to those without copper.…”

“…[38][39][40][41][42][43][44][45][46][47][48][49][50] The deposition of small amounts of copper with iron group metals ensures the obtainment of powders having an appropriate mean particle size, nanosized crystalline grains, good magnetic properties and high corrosion resistance. [51][52][53][54][55][56][57][58][59][60] Electrodeposited ternary nickel-cobalt-copper z E-mail: smilica84@yahoo.com alloys are used as magnetic or magnetoresistive materials, which have better corrosion resistance than the Co-Cu system. [51][52][53][54][55][56][57][58] Nanostructured alloys occur in a metastable state.…”

“…Annealing these alloys at elevated temperatures leads to heat-induced changes in their microstructure, which consequently affect their physical and chemical properties. [46][47][48]59,60 Annealing nanostructured alloys at temperatures below the crystallization temperature results in their structural relaxation, which involves short-range ordering. [46][47][48]59,60 At higher temperatures, amorphous phase crystallization and crystal grain growth take place, leading to changes in the mechanical, electrical, magnetic and corrosion properties of the alloy.…”

“…[46][47][48]59,60 Annealing nanostructured alloys at temperatures below the crystallization temperature results in their structural relaxation, which involves short-range ordering. [46][47][48]59,60 At higher temperatures, amorphous phase crystallization and crystal grain growth take place, leading to changes in the mechanical, electrical, magnetic and corrosion properties of the alloy. [46][47][48]59,60 The objective of this experiment was to examine the effect of the deposition of small amounts of copper with nickel and cobalt on the chemical composition, morphology and microstructure of electrodeposited Ni-Co-Cu alloys, and to evaluate the effect of these properties and annealing temperature on magnetic characteristics.…”