Int. J. Machining and Machinability of Materials, Vol. 17, No.

1, 2015 79

Electrochemical machining of 20MnCr5 alloy steel

with ferric nitrate mixed aqueous NaCl electrolyte

S. Ayyappan*
Government College of Engineering,
Salem – 636011, Tamilnadu, India
Email: ayyappansola@gmail.com
*Corresponding author

K. Sivakumar
Bannari Amman Institute of Technology,
Sathyamangalam – 638401, Tamilnadu, India
Email: ksk71@rediffmail.com

M. Kalaimathi
School of Mechanical and Building Sciences,
VIT University,
Vellore – 632014, Tamilnadu, India
Email: mkm1979@rediffmail.com

Abstract: Electrochemical machining (ECM) is a fast growing and widely used

advanced machining process. Improving a material removal rate (MRR) of
ECM is still a topic of concern in order to utilise its full potential. In this paper,
ferric nitrate (FeNO3) was included in small proportions in the aqueous NaCl
electrolyte solution in the direction of improving ECM performance. The
performance parameters i.e. MRR and surface roughness (Ra) have been greatly
improved by enhancing the ionisation of the electrolyte by this new mixture of
electrolyte. It was found that FeNO3 has suitable characteristics to mix
with NaCl to enhance the ionisation reaction. In this work, experimental
investigation was conducted to study the electrochemical machining
characteristics of 20MnCr5 alloy steel for both aqueous NaCl and FeNO3
mixed aqueous NaCl electrolytes. The significance of ECM process parameters
such as flow rate of electrolyte, tool feed rate, voltage and current on MRR and
Ra was analysed. Microstructure of surface of the specimen machined with
FeNO3 mixed aqueous NaCl electrolyte shows the improvement in surface
finish.

Keywords: electrochemical machining; ECM; material removal rate; MRR;

surface roughness; Ra; ferric nitrate; aqueous NaCl electrolyte; 20MnCr5 alloy
steel.

Reference to this paper should be made as follows: Ayyappan, S.,

Sivakumar, K. and Kalaimathi, M. (2015) ‘Electrochemical machining of
20MnCr5 alloy steel with ferric nitrate mixed aqueous NaCl electrolyte’,
Int. J. Machining and Machinability of Materials, Vol. 17, No. 1, pp.79–94.

Copyright © 2015 Inderscience Enterprises Ltd.

80 S. Ayyappan et al.

Biographical notes: S. Ayyappan is currently an Assistant Professor of

Mechanical Engineering in Government College of Engineering, Salem,
Tamilnadu, India. He graduated in Mechanical Engineering from Thiagarajar
College of Engineering, Madurai Kamaraj University, Tamilnadu, India. He
obtained his Master degree in Industrial Engineering from College of
Engineering Guindy, Anna University Chennai, Tamilnadu, India. His research
area of interest includes non-conventional machining techniques, optimisation
techniques, metal matrix composites and agile manufacturing. He is pursuing
his Doctoral degree in Mechanical Engineering from Anna University Chennai
under the guidance of Dr. K. Sivakumar. He has presented papers in ten
international conferences and eight national conferences and published papers
in nine international journals.

K. Sivakumar is working as Professor and Head of Mechanical Engineering in

Bannari Amman Institute of Technology, Sathyamangalam, Tamilnadu, India.
He received his BE in Mechanical Engineering from Government College of
Engineering, Tirunelveli, Madurai Kamaraj University, Tamilnadu, India. He
obtained his MTech in Quality Assurance Technology and PhD in Production
Engineering from National Institute of Technology, Tiruchirapalli, India. His
area of interest includes tolerance design, optimisation, quality engineering and
non-conventional machining techniques. He has published papers in 65 journals
and 85 conferences of international repute. He is guiding several research
scholars and eight of them were awarded PhD degree by Anna University
Chennai. He organised several workshops and conferences to his credit. He is
undertaking funded projects from AICTE. He was listed in Who’s Who 2011.

M. Kalaimathi is an external part time research scholar of School of

Mechanical and Building Sciences in VIT University, Vellore, Tamilnadu,
India. She is a Deputy Director of Industrial Safety and Health, Erode,
Government of Tamilnadu, India. She graduated in Mechanical Engineering
from Bharathidasan University, Tiruchirappalli, Tamilnadu, India. She obtained
her Master degree in Engineering Design from Government College of
Engineering, Tirunelveli, Anna University Chennai, Tamilnadu, India. She is
involving in research on electrochemical machining characteristics. She has
published papers in four international and two national journals and presented
papers in ten conferences.

This paper is a revised and expanded version of a paper entitled ‘Performance

study of electrochemical machining process by using ferric nitrate as a catalyst
in the electrolyte’ presented at the Proceedings of IETSD 2012, Bannari
Amman Institute of Technology, Sathyamangalam, Tamilnadu, India, 3–5
September 2012.

1 Introduction

Electrochemical machining (ECM) is capable of machining the materials which are very
difficult to cut by conventional machining techniques. ECM is a controlled anodic
dissolution process at atomic level of the work piece that is electrically conductive by a
shaped tool through an electrolyte as shown in Figure 1. In ECM, work piece is the anode
and the tool is cathode and the electrolyte is pumped through the gap between the tool
and the work piece, while direct current is passed through the cell, to dissolve metal from
the work piece.
 ECM of 20MnCr5 alloy steel with ferric nitrate mixed aqueous NaCl 81

Figure 1 Electrochemical machining process (see online version for colours)

As the material removal takes place due to atomic level dissociation, the surface is
machined with excellent surface finish and is stress free. The choice of electrolyte
strongly influences the performance of ECM. The material removal rate (MRR) is
proportionate to the conductance of electrolyte according to the Faraday’s law. The any
chance of increase in the conductance of electrolyte leads to more anodic dissolution.
This can be attained through high current density and increase in concentration of
electrolyte. More concentration of electrolyte will become a hindrance to the mobility of
ions, which results in poor conductance. The chance of increasing the conductance was
investigated using K2Cr2O7 mixed aqueous NaCl electrolyte (Ayyappan and Sivakumar,
2014b). The effective removal of sludge in the inter-electrode gap was also attempted
using oxygenated aqueous NaCl electrolyte (Ayyappan and Sivakumar, 2014a). The
surface structure was analysed during pulsed ECM of iron in NaNO3 electrolyte
(Rosenkranz et al., 2005). Fushimi et al. (2009) examined the anodic dissolution behavior
of titanium in chloride-containing ethylene glycol. Formation of electrochemical products
and its transition was discussed in the Lohrengel and Rosenkranz’s (2005) work. High
rate anodic dissolution of electro-thermochemically treated steel in chloride solutions was
studied by Silkin et al. (2008). Many research works have been carried out to improve the
anodic dissolution rate of ECM process with different salt solutions. High rate anodic
dissolution of 100Cr6 steel in aqueous NaNO3 solution was discussed by Haisch et al.
(2004). More participation of hydroxide ions makes high rate anodic dissolution of work
piece (Byk et al., 2004). It is clearly understood that more electrolyte conductance makes
more material removal. In this paper, work is aimed at improving the ECM performance
by adding ferric nitrate (FeNO3) in the aqueous NaCl electrolyte solution. It is known that
FeNO3 has suitable characteristics to mix with NaCl to enhance the oxidation reaction.
The 20MnCr5 alloy steels finds wide variety of mechanical applications in high stressed
automobile components such as gears, crankshafts and connecting rods, etc (Brnic et al.,
2014). The fracture behaviour of 20MnCr5 alloy steel was compared with S275JR steel
to understand its utility in specific applications (Vukelic and Brnic, 2014). In gear
manufacturing process, distortion minimisation of disks made up of 20MnCr5 alloy steels
was extensively studied (Brinksmeier et al., 2011). The above studies confirm the
massive utilisation of 20MnCr5 alloy steels and thus these steels are considered as testing
materials in this work.
82 S. Ayyappan et al.

2 Experimental investigation

2.1 Polarisation studies

Suitability and conductance of FeNO3 are tested with Tafel experiments. The 20MnCr5
alloy steel of 1 cm3 cube armoured in an araldite resin was taken as a working electrode.
This alloy steel samples contain chemical composition in mass (%) as in Table 1. It was
referred from Brnic et al.’s (2014) work.

Table 1 Chemical composition of test specimen

Material
Steel name EN (10084-2008)/(17210): 20MnCr5 AISI, steel number 1.7147
designation
Composition Fe C Mn Cr Si Ni Cu Nb S P Ti W Mo V Al
Mass (%) 96.7 0.22 1.23 1.11 0.29 0.08 0.06 0.03 0.025 0.021 0.02 0.02 0.01 0.01 0.01

The working surface of the electrode was polished with emery paper, washed in distilled
water and dried. The electrode was then placed in a glass three-electrode polarisation cell
which was connected with CH Instruments electrochemical analyser (Model 608E)
controlled by personal computer (Figure 2).

Figure 2 Electrochemical analyser (Model 608E) (see online version for colours)

Reference electrode

Working electrode
Electrochemical
analyser
Counter electrode

Saturated calomel electrode was taken as reference electrode to which all potentials are
referred. The counter electrode was a platinum plate of surface area of 1 cm2. The
working electrode (20MnCr5 alloy steel) was immersed in the test solution for
20 minutes until a steady state open circuit potential (Eocp) was obtained. The potential
was altered automatically from open circuit potential up to the range of –0.3 V to –0.9 V
and ran at scan rate of 0.002 V/s using software supplied by CH Instruments. Each
experiment was performed with freshly prepared solution and clean set of electrodes.
Measurements were conducted at 130,145,160 g/l concentration of analytical NaCl
solution. Figure 3 shows the Tafel plots for 20MnCr5 alloy steel in above NaCl
concentrations.
 ECM of 20MnCr5 alloy steel with ferric nitrate mixed aqueous NaCl 83

Figure 3 Polarisation curves for different concentrations of NaCl (g/l) (see online version
for colours)

The total current flown into the electrolytic cell was calculated using Tafel equation (1)
RT RT
E − E0 = ln i0 − ln i (1)
α a nF α c nF
where
E electrode potential (V)
0
E standard potential (V)
0
E–E over potential (V)
R universal gas constant (8.314 Jmol–1K–1)
F Faraday constant (96,500 C mol–1)
T temperature of electrolyte (°K)
io exchange current (A)
i current (A)
n valency number of working electrode
αa anodic charge transfer coefficient
αc cathodic charge transfer coefficient.
The anodic dissolution rate (CR) was calculated for each concentration of NaCl solution
according to Faraday’s law given in equation (2).
⎛ i ⎞⎛ M ⎞
CR = ⎜ ⎟ ⎜ ⎟ (2)
⎝ F ⎠⎝ n ⎠
where
CR anodic dissolution rate (g/min)
M molar mass of working electrode (g/mol).
84 S. Ayyappan et al.

Figure 4 Polarisation curve for 1% FeNO3 in aqueous NaCl (see online version for colours)

Figure 5 Polarisation curve for 3% FeNO3 in aqueous NaCl (see online version for colours)

Figure 6 Polarisation curve for 5% FeNO3 in aqueous NaCl (see online version for colours)
 ECM of 20MnCr5 alloy steel with ferric nitrate mixed aqueous NaCl 85

The maximum CR was obtained at 145 g/l solution. Thus the concentration of 145 g/l
was considered to test the concentration requirement of FeNO3. The three levels of
FeNO3 such as 1%, 3% and 5% concentration per litre of aqueous NaCl was considered.
More than 5% concentration of FeNO3 makes the solution brown colour and more acidic
and its large deposits were found on electrode after test. The cathodic and anodic
polarisation curves for 20MnCr5 alloy steel in 145 g/l NaCl in the presence of FeNO3 at
different concentrations have been recorded and presented in Figures 4–6.
Table 2 presents the values of corrosion current (Icorr), corrosion potential (Ecorr),
cathodic Tafel slope (βc), anodic Tafel slope (βa) and other polarisation parameters for
both aqueous NaCl and FeNO3 mixed aqueous NaCl solutions. In the polarisation
method, the relation (3) determines the additive efficiency (AE %).
⎛ CR o ⎞
AE (%) = ⎜ 1 − ⎟ ∗100 (3)
⎝ CR ⎠
where CRo and CR are the anodic dissolution rates of alloy steel without and with FeNO3,
respectively.
Table 2 Polarisation parameters for 20MnCr5 alloy steel in different concentrations of FeNO3
mixed aqueous NaCl

Tafel plots
Electrolyte Cathodic Anodic Linear
Ecorr βa –βc Icorr × 10–3 intercept intercept polarisation AE
(V) (1/V) (1/V) (A) (%)
(log i) (log i) (ohm)
Aqueous 130 –0.579 3.998 4.916 0.00015 –6.942 –7.088 326,646 -
NaCl (g/l) 145 –0.726 10.823 8.264 0.05912 –4.258 –4.218 385 -
160 –0.659 4.900 4.990 0.00157 –5.943 –5.943 28,038 -
FeNO3 (%) 1 –0.551 3.354 5.924 0.00013 –7.013 –7.053 365,580 -
in 145 g/l 3 –0.555 6.183 3.229 2.522 –2.777 –2.731 18 97.7
aqueous
NaCl 5 –0.531 5.396 3.936 3.265 –2.623 –2.659 14 98.2

The polarisation curves of 20MnCr5 alloy steel in aqueous NaCl with and without the
FeNO3 show that the addition of the additive increases the anodic current densities. The
additive efficiency reaches the maximum of 98% at 5% FeNO3 in 145 g/l aqueous NaCl
solution. Anodic dissolution rate was accelerated more with change in pH value of
electrolyte.
The electrolyte and water undergoes ionic dissociation (Trasatti, 2009a, 2009b) as the
potential difference is applied through electrochemical cell between anode and cathode.
The cations move towards the cathode and anions move towards the anode.
Aqueous NaCl solution dissociates as
NaCl → Na + + Cl− and H 2 O → H + + (OH) − (4)

The working electrode of 20MnCr5 alloy steel undergoes reaction as

Fe0 → Fe n + + ne − (5)
86 S. Ayyappan et al.

Hydroxyl ion (OH − ) evolves oxygen at the anode as

4OH − → O 2 ↑ +2H 2 O + 4e − (6)

When no metal dissolution occurs, the oxygen formation is dominated. In aqueous NaCl
solution, oxygen formation is less. The hydrogen ions will take away electrons and form
hydrogen gas at the cathode.

2H + + 2e − → H 2 ↑ (7)

Choking of the flow of electrolyte by hydrogen bubbles is avoided by the high velocity of
electrolyte jet. Sodium ions combine with hydroxyl ions to form sodium hydroxide.

Na + + OH − → NaOH (8)

Fe 2 + + 2OH − → Fe(OH) 2 (9)

Addition of ferric nitrate leads to the reaction further as

FeNO3 + 3NaOH → Fe(OH)3 + 3NaNO3 (10)

NaNO3 + H 2 O → NaOH + HNO3 (11)

Presence of more Fe(OH)3 makes the electrolyte bit acidic which supports the increase in
dissolution rate (Sharma et al., 2002; Thanigaivelan et al., 2013). Formation of NaNO3
also contributes to more anodic dissolution since it posses good ionic bond. The above
studies confirm that the addition of FeNO3 in the aqueous NaCl solution certainly
increases the anodic dissolution rate, which enthralled the authors to study about the
influence of ECM process parameters with above electrolyte on MRR and surface
roughness (Ra).

2.2 Experiments in ECM

Commercially obtained 20MnCr5 alloy steel specimen with Φ 40 mm diameter and
10 mm length was used for the ECM experiments. Aqueous NaCl solution was used as an
electrolyte. Copper tool with square end was used as a cathode and its 3D model is shown
in Figure 7. Figure 8 shows an experimental set up of the ECM system used in this work.
The main process parameters governing the ECM process are voltage (V) setting, tool
feed rate (F), electrolyte flow rate (U) and current (i) according to the literature (Asokan
et al., 2008; Senthilkumar et al., 2009). Therefore, these parameters are considered in this
work to understand the significance on ECM performance. Other parameter,
inter-electrode gap was kept constant (0.1 mm) during experimentation because of the
fact that current density is more at small inter-electrode gap. In ECM, the current density
is usually high. At low current densities, the MRR is low. In order to have more material
removal of the anode, a sufficient amount of current has to be given. The NaCl and
FeNO3 concentration are fixed as 145 g/l of water and 5% in aqueous NaCl solution
respectively according to polarisation studies (Section 2.1). The process parameters and
its range considered in this work are as follows.
 ECM of 20MnCr5 alloy steel with ferric nitrate mixed aqueous NaCl 87

• feed rate (F): 0.1–0.54 mm/min

• voltage (V): 15–25 volts
• flow rate (U): 6–10 l/min
• current (i): 220–260 A.

Figure 7 3D model ECM tool (see online version for colours)

Figure 8 Electrochemical machining set-up (see online version for colours)

Pressure Control panel

gauge

Flow
meter

Machining
Electrolyte chamber
tank
88 S. Ayyappan et al.

Machining process was carried out for nine various set of parameters according to the
Taguchi technique (L9 orthogonal array), and the MRR was calculated based on loss of
weight and tabulated. By using the Sartorious weighing balance, weights were measured.
Ra was measured using Mitutoyo surface roughness tester. Table 3 shows the results for
MRR, Ra in all cutting conditions for both electrolytes. The samples before and after
machining are shown in Figure 9.

Figure 9 Pictures of specimen, (a) before machining (b) after machining (with FeNO3 mixed
aqueous NaCl) (see online version for colours)

(a) (b)

Table 3 Results of MRR and Ra for different electrolytes

Flow Feed NaCl electrolyte With FeNO3

Voltage Current
rate rate
(V) (C) MRR Ra MRR Ra
(U) (F)
V A (g/min) (µm) (g/min) (µm)
l/min mm/min
1 6 0.1 15 220 0.1912 6.54 0.2375 1.54
2 6 0.32 20 240 0.2242 5.44 0.2450 1.84
3 6 0.54 25 260 0.1996 5.41 0.2620 2.41
4 8 0.1 20 260 0.1871 3.26 0.2428 1.56
5 8 0.32 25 220 0.2262 4.17 0.2906 1.17
6 8 0.54 15 240 0.1963 5.32 0.2548 1.97
7 10 0.1 25 240 0.2125 3.17 0.2761 1.98
8 10 0.32 15 260 0.2006 3.42 0.2512 1.42
9 10 0.54 20 220 0.2088 5.23 0.2455 1.25

3 Analysis of MRR

Figure 10 shows that MRR was more with NaCl electrolyte mixed with FeNO3. MRR
was increased due to increase in conductance by the presence of FeNO3. Ferric nitrate is a
good oxidation agent and NaOH base is improved in the electrolyte solution. MRR
 ECM of 20MnCr5 alloy steel with ferric nitrate mixed aqueous NaCl 89

was influenced more by fifth test conditions (U = 8 l/min, F = 0.32 mm/min, V = 25 V,

i = 220 A), fourth test condition (U = 8 l/min, F = 0.1 mm/min, V = 20 V, i = 260 A)
produces low metal removal. Though current is more in this condition, feed rate (F) is
very low which in turn produces poor dissolution process. Figures 11 and 12 show the
relationship between feed rate, current and MRR for aqueous NaCl electrolyte and
FeNO3 mixed aqueous NaCl electrolyte.

Figure 10 Comparison of MRR with different electrolytes (see online version for colours)

0.35
Material removal rate (MRR) g/min

0.3
0.25
0.2
MRR with NaCl
0.15 electrolyte
0.1 MRR with NaCl and
FeNO3 electrolyte
0.05
0
1 2 3 4 5 6 7 8 9
Tests

The sludge produced during machining hampers the uniform anodic dissolution of
material from the work piece, which results in lower MRR. During the ECM with
NaCl, MRR is more at the feed rate (F) of 0.3 mm/min for all current conditions.
Other parameters do not affect significantly the MRR. According to Figures 11 and 12,
at feed rate of 0.3 mm/min, current of 220 A, MRR is more. It is observed that current is
significantly affecting MRR. The presence of FeNO3 increases the conductance of
electrolyte and its presence removes the sludge formed during machining.

Figure 11 Influence of feed rate (F) on MRR with aqueous NaCl electrolyte (see online version
for colours)

0.25
Material removal rate (MRR)

0.2
0.15
Current 220 Amps
g/min

0.1
Current 240 Amps
0.05
Current 260 Amps
0
0 0.2 0.4 0.6
Feed rate(F) mm/min
90 S. Ayyappan et al.

Figure 12 Influence of feed rate (F) on MRR with FeNO3 mixed aqueous NaCl electrolyte
(see online version for colours)

0.35
Material removal rate (MRR)

0.3
0.25
0.2
0.15 Current 220 Amps
g/min

0.1 Current 240 Amps

0.05 Current 260 Amps
0
0 0.2 0.4 0.6
Feed rate(F) mm/min

4 Analysis of Ra

Figure 13 shows the comparative results of Ra for both aqeuous NaCl and FeNO3
mixed aqeuous NaCl electrolytes. Best test conditions for better Ra is U = 6 l/min,
F = 0.1 mm/min, V = 15 V, i = 220 A. Seventh test conditions (U = 10 l/min,
F = 0.1 mm/min, V = 25 V, i = 240 A) provides poor Ra value.

Figure 13 Comparative study of Ra for different electrolytes (see online version for colours)

7
Surface roughness (Ra) µm

6
5
4 Ra with NaCl
3 electrolyte
2 Ra with NaCl and
FeNO3 electrolyte
1
0
1 2 3 4 5 6 7 8 9
Tests

Figures 14 and 15 show the results for Ra for flow rates and current. It can be observed
that the lower Ra is obtained for current of 240 A and 260 A at the flow rate of 10 l/min.
It is observed that at the flow rate of 10 l/min, Ra is low for all current conditions. It can
be observed that flow rate is significantly affecting the Ra.
 ECM of 20MnCr5 alloy steel with ferric nitrate mixed aqueous NaCl 91

Figure 14 Influence of flow rate (U) in Ra with NaCl electrolyte (see online version for colours)

7
Surface Roughness (Ra) µm
6
5
4
Current 220 Amps
3
Current 240 Amps
2
Current 260 Amps
1
0
0 5 10 15
Flow rate(U) l/min

Figure 15 Influence of flow rate (U) on Ra with FeNO3 mixed aqeuous NaCl electrolyte
(see online version for colours)

3
Surface Roughness (Ra) µm

2.5

1.5 Current 220 Amps

1 Current 240 Amps
0.5 Current 260 Amps

0
0 5 10 15
Flow rate(U) l/min

5 Micrograph analysis

Figure 16(a) shows the image of surface structure of test specimen machined with
aqueous NaCl solution. Heterogeneous surface structure is formed with aqueous NaCl
solution. White spots in the image are ferrite. Block dots on the surface structure shows
the metal carbides in the steel matrix. Figure 16(b) represents the surface structure of
specimen machined with ferric nitrate mixed with aqueous NaCl solution. More carbide
particles are clearly visible in steel matrix because of the high anodic dissolution of
ferrous. The surface is a well defined homogeneous structure. Major contribution of ferric
nitrate is to enhance the acidic nature of electrolyte. This new electrolyte mixture reduces
the production of byproducts, which in turn reduces Ra on specimen. Block dots on the
92 S. Ayyappan et al.

structure is carbides and small amount of non-metallic inclusion compounds. It does not
electrochemically dissolve. But it is mainly washed away with electrolyte jet. No surface
layer is found on the images given below.

Figure 16 Image of machined surfaces, (a) aqueous NaCl electrolyte (b) aqueous NaCl electrolyte
with ferric nitrate

100 µm (150× magnification) 100 µm (150× magnification)

(a) (b)

6 Conclusions

The influence of the flow rate, feed rate, machining voltage and current on the MRR and
Ra for the electrolyte of ferric nitrate mixed sodium chloride have been investigated
experimentally. Based on the studies conducted, the following conclusions have been
made:
1 The polarisation studies with FeNO3 mixed aqueous NaCl electrolyte confirms the
increase in the anodic dissolution rate.
2 MRR and Ra are significantly influenced by the addition FeNO3 in aqueous NaCl
electrolyte for ECM.
3 Feed rate of 0.3 mm/min is found to be producing more MRR at all current
conditions for both electrolytes.
4 Ra is lowered with ferric nitrate (FeNO3) mixed with aqueous NaCl solution. This is
due to uniform atomic dissolution which was supported by effective removal of
sludge.
5 It is observed that flow rate significantly affect the Ra.
6 Surface structure of machined work piece with ferric nitrate mixed with aqueous
NaCl electrolyte appears to be very good.
7 The present results provide the necessary information about the enhanced
performance of ECM with FeNO3 mixed aqueous NaCl electrolyte.
 ECM of 20MnCr5 alloy steel with ferric nitrate mixed aqueous NaCl 93

Acknowledgements

The authors would like to thank World Bank for funding ECM apparatus and
electrochemical analyser at Government College of Engineering, Salem-636011,
Tamilnadu, India under TEQIP scheme.

References
Asokan, P., Ravikumar, R., Jeyapaul, R. and Santhi, M. (2008) ‘Development of multi-objective
optimization models for electrochemical machining process’, International Journal of
Advanced Manufacturing Technology, Vol. 39, Nos. 1–2, pp.55–63.
Ayyappan, S. and Sivakumar, K. (2014a) ‘Experimental investigation on the performance
improvement of electrochemical machining process using oxygen-enriched electrolyte’,
International Journal of Advanced Manufacturing Technology, Vol.75, Nos. 1–4, pp.479–487.
Ayyappan, S. and Sivakumar, K. (2014b) ‘Investigation of electrochemical machining
characteristics of 20MnCr5 alloy steel using potassium dichromate mixed aqueous NaCl
electrolyte and optimization of process parameters’, Proceedings of Institution of Mechanical
Engineers Part B: J. Engineering Manufacture, pp.1–13, DOI: 10.1177/0954405414542136.
Brinksmeier, E., Lubben, T., Fritsching, U., Cui, C., Rentsch, R. and Solter, J. (2011) ‘Distortion
minimization of disks for gear manufacture’, International Journal of Machine Tools &
Manufacture, Vol. 51, No. 4, pp.331–338.
Brnic, J., Turkalj, G., Lanc, D., Canadija, M., Brcic, M. and Vukelic, G. (2014) ‘Comparison of
material properties: steel 20MnCr5 and similar steels’, Journal of Constructional Steel
Research, Vol. 95, pp.81–89.
Byk, M.V., Tkalenko, D.A. and Tkalenko, M.D. (2004) ‘On participation of hydroxide ions in the
anodic dissolution of metals in aqueous electrolyte solutions’, Protection of Metals, Vol. 40,
No. 3, pp.294–296.
Fushimi, K., Kondo, H. and Konno, H. (2009) ‘Anodic dissolution of titanium in chloride-
containing ethylene glycol solution’, Electrochimica Acta, Vol. 55, No. 1, pp.258–264.
Haisch, T., Mittemeijer, E.J. and Schultze, J.W. (2004) ‘High rate anodic dissolution of 100Cr6
steel in aqueous NaNO3 solution’, Journal of Applied Electrochemistry, Vol. 34, No. 10,
pp.997–1005.
Lohrengel, M.M. and Rosenkranz, C. (2005) ‘Micro electrochemical surface and product
investigations during electrochemical machining (ECM) in NaNO3’, Corrosion Science,
Vol. 47, No. 3, pp.785–794.
Rosenkranz, C., Lohrengel, M.M. and Schultze, J.W. (2005) ‘The surface structure during pulsed
ECM of iron in NaNO3’, Electrochimica Acta, Vol. 50, No. 10, pp.2009–2016.
Senthilkumar, C., Ganesan, G. and Karthikeyan, R. (2009) ‘Study of electrochemical machining
characteristics of Al/SiCp composites’, International Journal of Advanced Manufacturing
Technology, Vol. 43, Nos. 3–4, pp.256–263.
Sharma, S., Jain, V.K. and Shekhar, R. (2002) ‘Electrochemical drilling of inconel superalloy with
acidified sodium chloride electrolyte’, International Journal of Advanced Manufacturing
Technology, Vol. 19, No. 7, pp.492–500.
Silkin, S.A., Pasinkovskii, E.A., Petrenko, A.I. and Dikusar, V.I. (2008) ‘High rate anodic
dissolution in chloride solutions of steel after electrothermochemical treatment’, Surface
Engineering and Applied Electrochemistry, Vol. 44, No. 5, pp.343–352.
Thanigaivelan, R., Arunachalam, R.M., Karthikeyan, B. and Loganathan, P. (2013)
‘Electrochemical micromachining of stainless steel with acidified sodium nitrate electrolyte’,
The Seventeenth CIRP Conference on Electro Physical and Chemical Machining (ISEM),
Procedia CIRP, Vol. 6, pp.351–355.
94 S. Ayyappan et al.

Trasatti, S. (2009a) ‘Hydrogen evolution’, Electro Chemical Theory, Reference Module in

Chemistry, Molecular Sciences and Chemical Engineering, Encyclopedia of Electrochemical
Power Sources, pp.41–49, Elsevier, Inc., Amsterdam.
Trasatti, S. (2009b) ‘Oxygen evolution’, Electro Chemical Theory, Reference Module in Chemistry,
Molecular Sciences and Chemical Engineering, Encyclopedia of Electrochemical Power
Sources, pp.49–55, Elsevier, Inc., Amsterdam.
Vukelic, G. and Brnic, J. (2014) ‘Prediction of fracture behavior of 20MnCr5 and S275JR
steel based on numerical crack driving force assessment’, Journal of Materials in Civil
Engineering, Vol. 27, No. 3, 04014132, pp.1–4.