Effect of Ni Concentration in Cu-Fe-Ni alloys Coating on mild steel substrate Prepared by Electrochemical Deposition

Mild steel has applications in construction, automobiles, mechanical engineering and general purpose fabrication, fencing, cages, frames, furniture components for different shapes, pipelines and other in industries. Cu-Fe-Ni alloy coating with different concentration of Ni was produced on low carbon steel substrate by electrodeposition in this research. This technique is favorable to us because of its low cost and easy to approach. The electrolytic bath contained the 31.92g/l CuSO 4 , 54.2 g/l FeSO 4 , NiSO 4 .7H 2 O (0.00 g/l, 14.04 g/l, 28.08 g/l, 42.12 g/l) and 15.4 g/l H 3 BO 3 as buffer to maintain pH at 3 . The electrodeposition is done at suitable deposition parameters. The effect of Ni concentration on the surface morphology, structure and mechanical properties of coating were revealed by scanning electron microscope (SEM), X-ray diffraction (XRD) analysis and Vicker hardness tester respectively. Obtained results showed that with the increase in Ni content grain size increases and elongation decreases while the mechanical properties increases. The thickness of deposited Cu-Fe-Ni alloys has decreasing trend of thickness with increasing of Ni contents.


Introduction
Fe-Ni alloys have the lowest thermal expansion coefficient and strong magnetic performance [1].Hence Fe-Ni alloys have wider common usage in today's evolving and expending heavy industries of aerospace, electronics and machine building (mechanics).because of its better deposition quality, fast productivity and low cost the technology of electrodeposition offers new scenarios in electronic fabrication businesses.e.g. it has been widely used in recording heads to deposit magnetic alloy on it [2].Different types of alloys are formed to have greater tensile strength then their metals themselves, hence there is always a greater ever increasing use of various kinds of alloys in modern day's metal industry.The common use of stainless steels is in house hold products and construction machinery [3].The other common examples of alloy uses is in ornamental jewelry made with gold.The gold is used in form of alloys due to the high malleability of pure gold metal.On the other hand the alloys of brass and bronze are mostly used in making of musical instruments, decorative pieces, locks and zippers etc [1].
Due to the most important properties of sustainability, elasticity, corrosion resistance, strength or shape memory, a number of alloys are used in electrical, mechanical, medical and likewise many other sophisticated engineering groups.The most common examples of alloy uses are aluminum alloys.The aluminum alloys have comparatively greater tensile durability and strength then the metal itself which makes it lighter and equally durable medium fit for construction of large engines and their parts and airplanes body frames or wings.Wind turbines, modern building structures and military equipment's have greater and ever increasing usage of this alloy for its cost effectiveness, lightness and durability.
Cu-Ni alloys have the unique tendency of shape memory and truly are justified to be called shape memory alloys (SMA's).Copper (Cu) not only increases the corrosion resistance in its Ni-Ti SMA's alloys but also it has the striking biological features like antibacterial activities [4].The presence of Cu in Cu-Ti-Ni SMA's improves the shape memory behavior of above mentioned alloy.It makes it easier to go casting [5] and making it the best medium for orthodontic wires widely used in dentistry.Ni and Cu helps in enhancing mechanical properties and strength of Titanium.It also increases the antibacterial capabilities of the alloys [6].
Electrodeposition technology offers new prospects in the microelectronic fabrication businesses in these days.
The characteristics and morphology of deposits are significantly influenced by the electrodeposition conditions.The electrodeposition of Fe-Co alloys in Different solution has been discovered for nearly two decades [7][8][9].Several additives get considerable attention due to their positive influence on electrolytic bath stability and quality of the deposition which forms during the process.The most frequently used additive to improve the features of the Fe group alloys is saccharin [10][11][12].As it has the tendency to reduce the tensile strength, improved grain size and roughness [13].The experiments show that during the process of electroplating, the Sulphur atom present in the sulphone group of sodium saccharin reduces sulphide ion during the electrochemical process which incorporates itself in to the deposits [14].Sodium propargyl sulfonate was proven to be a good addition for reduction of internal stresses and the refinement of grains in the Fe-Co deposits.The internal forces appear to be an important source of coercion.Lower coercivity is usually equated by the reduced stress [15].On the contrary, no electrodeposition of Fe-Co alloy in Sodium propargyl sulfonate solution have been formed yet.
Mild steel has applications in construction, automobiles, mechanical engineering and general purpose fabrication, fencing, cages, frames, furniture components for different shapes, pipelines and fences for business and homes and other industries, but it has weak mechanical properties, degrades and corrode easily.To cover these problems we use the Ni in Cu-Fe alloy because Ni has all the properties related to that problem.Nickel is very important and widely used in alloy steels.It is ideal for solid solution to make strengthen, a hardenability agent and very important to promote high toughness at low temperature.Ni helps to cover corrosion, heat resistance and scratches.Ni also increase the elastic limit of mild steel.When Ni alloy is coated on steel, its hardness and density increases.It also improve resistance to corrosion and oxidation.Hence, if we coated Cu-Fe alloy with different concentration of Ni it covers most of the problems that we face in mild steel.

Materials and methodology
Four different plating baths were prepared containing NiSO 4 , FeSO 4 and CuSO 4 .All baths were prepared at 40 °C.FeSO 4 and CuSO 4 concentration was kept constant at 31.92 (g/l) concentration in all the four baths while NiSO 4 concentration was varied as 0, 14.04 g/l, 28.08 g/l and 42.12 g/l.The low nickel content in the baths was taken to ensure diffusion controlled deposition of nickel.15.4 g/l boric acid was added to solution as a buffer.2.5 g/l saccharin was used to maintain the pH of the solution.The pH of the baths was adjusted to 3. All chemicals used were of laboratory grade.
Electrodeposition experiments were carried out for all four baths in galvanostatic mode.The bath composition and operating parameters for electrodeposition are given in Table 1.The anode were placed on the front side of the cathode to maintain uniformity of coating on one side of the steel substrate.Magnetic stirring was also employed for well mixing before each experiment, samples were rinsed with distilled water and electrodeposition was carried out immediately to ensure no oxide film forms on the surface before deposition.Masses of the dried substrates were measured by a weight balance (Sartorius BSA 224S-CW) before and after the deposition.The initial mass was subtracted from the final mass to get the actual mass of the coating.This mass was used in the calculation of the thickness of the coating.Scanning electron microscopy was performed using a FESEM (Carl Zeiss AG -Supra 25) to understand the coating surface morphology and microstructure.The XRD patterns were obtained using an X-ray source with a 45 kV accelerating voltage and a 40 mA emission present.

Results and Discussion
The thickness of the deposited alloy was calculated by using the following equation.
Where 't' is the thickness of the deposited material and 'm' is the mass that is deposited on the substrate and 'A' is the area of deposited material and 'ρ' is the average density of deposited alloy.The data obtained from Eq. ( 1) is   deposited on the surface.The decrease in thickness could be related to decrease in deposition mass [16].
X-ray diffractometer is used to determine the lattice parameters, phase structure and grain size of binary Cu-Fe as well as ternary Cu-Fe-Ni alloys.Results obtained from x-ray diffraction analysis are given in Table 3.The effect of Ni concentration on the structure of ternary alloy Cu-Fe-Ni coating is shown with the XRD patterns in Fig. 2 The reflection have a face centered cubic.(fcc) structure and the crystal planes in all coating are (111), ( 200) and (220) at different 2θ angles 43.408°, 50.445° and 73.799° are detected [17].[20].While the increase in crystallite size can be attributed to increase in lattice constant [21].
The influence of electrolyte composition on the surface morphology of coatings is shown in Fig. 4 (b-c) represents the surface morphology of un-doped NiSO 4 .The surface of Cu-Fe coating has smaller grain size of 5.66 μm with relatively partial nodule structure.Increasing the Ni concentration significantly affects the surface morphology.

Fig. 4 Surface morphology of Cu-Fe-Ni alloys without and with Ni contents
As the Ni content of the alloy increased, the grain size is observed to increase up to 16.25 μm in Cu-Fe-Ni alloy coatings element and this effect is may be caused by the formation of Cu-rich intermetallic prior to the nucleation of α-Fe dendrites [22].By increasing the Ni content, This little nodule structure also changes to globular structure [23].
Results of micro-hardness thin films before and after doping of nickel with different concentration are shown in Table 5.  5. From the graph it is clear that with the increase in concentration of nickel the ultimate tensile stress as well as hardness of the material also increases.
It is exhibited from the Table 5 that the UTS and hardness of first sample is 308.499 and 402.835 respectively when no nickel is added in the solution.Then UTS and hardness increases to almost 3% and 13% when nickel is added in the solution and it continuously increases.While for the last sample of maximum nickel content UTS and microhardness increases approximately 5% and 24% greater than when nickel is absent in the deposition.The increase in hardness and UTS must be related to the formation of Cu-and Ni-rich intermetallic.It is possible that an increase in contiguity in the 3D-network is responsible for the increase in hardness and UTS [24].These results are in accordance with the results reported by Kaya et al [25,26].To clarify the mechanical behavior of the coating, their elastic modulus and yield stress is taken as a function of nickel content presented in Fig. 6.From the graph it is clear that there is continuously increment in the elastic modulus and yield stress of the coating.The elastic modulus and yield strength of the substrate is 200.236GPa and 240.922MPa respectively as given in Table 6.But as Cu-Fe alloy is deposited on substrate the elastic modulus and yield strength increases to almost 2.7% and 6% respectively.When nickel concentration is added in deposition, these number continuously increases and reach to 7.3% and 12% respectively.It is reflected from the graph that the elastic modulus and yield strength of the sample with the lowest content of nickel is approximately 4.5% and 9% more than substrate while the yield strength of specimen with the highest nickel content reaches to 7.3% and 12% respectively more than substrate as mentioned earlier.The increase in coating elastic modulus yield stress can be attributed to the higher elastic modulus and yield stress value of nickel particles with the increase of their contents as compared to other elements i.e. copper and iron [27,28].
drawn between thickness of an investigated alloys and different Ni concentration as shown in Fig.1

Fig. 1
Fig. 1 Concentration of Ni verses the thickness of the coating Cu-Fe-Ni alloy

Fig. 3
Fig. 3 Concentration of Ni verses Lattice Constant

Fig. 5
Fig. 5 Concentration of nickel verses UTS and Micro-hardness of Cu-Fe-Ni alloy coatings

Fig. 6
Fig. 6 Concentration of nickel verses Micro-hardness of Cu-Fe-Ni alloy coatings

Fig. 7
Fig. 7 Elongation as a function of Concentration of nickel

Table 1 .
Bath compositions for electrodeposition of all samples

Table 2 :
Deposited mass and thickness of Cu-Fe-Ni coating

Table 3 :
Structure parameters obtained from XRD data for Cu-Fe-Ni alloys

Table 4 :
Crystallite size and lattice constant with different Ni concentration.
increases.It is exhibited from the graph that crystallite size and lattice constant of first sample is 30.503nm and 3.6075 respectively when no Ni is added.

Table 5 :
Ultimate tensile stress and micro-hardness of Cu-Fe-Ni alloy coatings with different concentration of Ni

Table 6 :
Elastic modulus and yield stress of Cu-Fe-Ni alloy coatings with different concentration of Ni.

Table 7 :
[24,26]ion of Cu-Fe-Ni alloy coatings with different Concentration of Ni.Fe alloy is 39.780 and decreases continuously.When nickel is added in the deposition it continuously decreases further.When first concentration of nickel which is 14.04 g/l as shown in table 4. Is added in the deposition, elongation decreases to 38.453.While as nickel content increases elongation decreases to 37.033 and these results are in accordance with the results reported in the literature[24,26].
In Fig.7elongation is taken as a function of nickel content as shown in graph.From the graph it is clear that with the increase in concentration of nickel the elongation decreases.It is exhibited from the graph that elongation of first sample Cu-