P. VENUGOPAL et al.: EFFECT OF ELECTROCHEMICAL PROCESS PARAMETERS ON THE HASTELLOY C-276 ALLOY ...
675–680
EFFECT OF ELECTROCHEMICAL PROCESS PARAMETERS ON
THE HASTELLOY C-276 ALLOY FOR MACHINING SPEED AND
SURFACE-CORROSION FACTOR
VPLIV PARAMETROV ELEKTROKEMIJSKIH PROCESOV NA
SUPERZLITINO HASTELLOY C-276 GLEDE NA HITROST
MEHANSKE OBDELAVE IN KOROZIJO POVR[INE
P. Venugopal
1*
, Thayammal Ganesan Arul
2
, V. Selvam
3
, K. Saranya
4
1
Muthayammal College of Engineering, Namakkal, Tamilnadu-637408, India
2
St Mary’s Engineering College, Hyderabad, Telangana-508284, India
3
Kongunadu College of Engineering and Technology, Tiruchirappalli,Tamilnadu-624215, India.
4
Government College of Engineering, Thanjavur,Tamilnadu-613402, India
Prejem rokopisa – received: 2023-08-29; sprejem za objavo – accepted for publication: 2023-10-30
doi:10.17222/mit.2023.981
Electrochemical micromachining (ECMM) is a well know for manufacturing hard-to-cut materials, e.g., nickel-based alloys, ti-
tanium alloys and metal-matrix composites. For this reason it finds application in aerospace, automobile and biomedical indus-
tries. In this research Hastelloy C-276 is used as a workpiece and stainless-steel electrode coated with polytetrafluoroethylene
(PTFE) to avoid stray current. The effect of process parameters such as voltage, duty cycle and electrolyte concentration on the
machining speed and the surface-corrosion factor were studied. The range of 9–11 V has an impact on the machining speed. The
electrolyte concentration range of 25–35 g/L shows a linear increase in the machining speed and the surface-corrosion factor is
found to be highest at 1.1449 for an electrolyte concentration of 15g/L. The surface roughness depth profile depicts the values of
Rz, Rt, Ra are 16.3 μm, 99.1 μm and 1.90 μm, and 15.4 μm, 50.6 μm and 1.49 μm, respectively.
Keywords: Hastelloy C-276, polytetrafluoroethylene, surface-corrosion factor, stray current, coating
Elektrokemijska mehanska obdelava povr{ine (ECMM; angl.: Electrochemical micromachining) je zelo dobro znana obdelava
za rezanje trdih materialov kot so zlitine na osnovi niklja, zlitine na osnovi titana in kompoziti s kovinsko osnovo. Zato ECMM
lahko najdemo v aplikacijah za letalsko, avtomobilsko in biomedicinsko industrijo. V tem ~lanku avtorji opisujejo raziskavo pri
kateri so uporabili preizku{ance iz nikljeve proti koroziji odporne superzlitine vrste Hastelloy C-276 in elektrodo iz nerjavnega
jekla prevle~eno z politetrafluoroetilenom (PTFE), da bi se izognili zablodelim elektri~nim tokovom (angl.: stray current).
Avtorji so {tudirali vpliv procesnih parametrov, kot so: elektri~na napetost, ~as obdelave in koncentracija elektrolita na hitrost
mehanske obdelave ter faktorje, ki vplivajo na povr{insko korozijo. Avtorji v ~lanku ugotavljajo, da ima napetost v obmo~ju
med9Vin11Vpomemben vpliv na hitrost obdelave. V obmo~ju koncentracije elektrolita med 25 g/L in 35 g/L so avtorji
ugotovili linearno nara{~anje hitrosti obdelave in ugotovili so, da je faktor povr{inske korozije vi{ji od 1,1449 pri koncentraciji
elektrolita 15 g/L. Ugotovljene vrednosti globine povr{inske hrapavosti so bile za Rz, Rt in Ra 16,3 μm, 99,1 μm in 1,90 μm
oziroma 15,4 μm, 50,6 μm in 1,49 μm.
Klju~ne besede: zlitina vrste Hastelloy C-276, elektrokemijska mikromehanska obdelava, politetrafluoroetilen, factor povr{inske
korozije, raztreseni (zablodeli) elektri~ni tokovi, opla{~enje
1 INTRODUCTION
Electrochemical micromachining (ECMM) is a non-
traditional machining method for manufacturing parts
with good surface quality and production rate. In ECMM
the tool (cathode) and workpiece (anode) are kept in an
electrolyte bath and while the application of the potential
difference across the electrodes material removal occurs
at the workpiece. By controlling the various factors such
as electrical parameters and electrolyte concentration,
controlled material removal happens in the workpicece.
ECMM finds application in various fields ranging from
aerospace to biomedical engineering. Research on
ECMM in past decades focused on improving the pro-
duction rate, accuracy and surface property. Venugopal et
al.
1
used a polytetrafluoroethylene (PTFE)-coated elec-
trode to improve the machining rate and overcut. They
reported that the electrolyte concentration shows the ma-
jor contribution for improving the conicity of the mi-
cro-hole. VinodKumaar et al.
2
used copper powder in the
electrolyte along with stirring mechanism to improve the
machining rate and the overcut. The use of a suspended
electrolyte with stirring effect produces higher MRR and
moderate overcut.Venugopal et al.
3
used a magnetic field
effect and graphite electrode and reported that graphite
and magnetic electrodes resulted in 11.9 % and 3.41 %
reduced OC, compared to a stainless-steel tool. Rajan et
al.
4
machined metal-matrix composites using ECMM
and reported that a metal-matrix composite with 10%
B
4
C shows good machinability. Thanigaivelan et al.
5
re-
ported the impact of tool-tip shape, i.e., flat shape, trun-
cated and conical shape, on the machining rate and
Materiali in tehnologije / Materials and technology 57 (2023) 6, 675–680 675
UDK 620.197:544.6.018 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(6)675(2023)
*Corresponding author's e-mail:
venunaveen73@yahoo.com (P. Venugopal)

overcut. They concluded that the tool-tip shape has an
impact on machining rate and overcut. Kumarasamy et
al.
6
used a variety of electrolytes, i.e., sodium nitrate, so-
dium chloride and mix of all these electrolytes with citric
acid to improve the material removal rate, overcut,
conicity and circular holes. They reported that the mixed
electrolyte improves all these output performances.
Panigrahiet al.
7
machined Hastelloy C -276 using
ECMM and noticed broken grains and inflated grain
boundaries with a spreading crack due to the stray cur-
rent corrosion. Gobinath et al.
8
showed that electrolytes
mixed with nanoparticles play an important role in
ECMM with an increase in MRR and a decrease in
cross-section and surface roughness at the optimized pa-
rameter setting level with a processing voltage of 7 V
and an electrolyte concentration of 5 g/L and a nano-
powder suspension of 5 g/L. Liu et al.
9
reviewed the
ECMM for metallic workpieces. They have studied the
effect of electrodes, electrolytes on the surface properties
of the metallic workpieces. They concluded that these
parameters have an impact on the surface quality of met-
als machined in ECMM. Thangamani et al.
10
studied the
influence of three electrolytes, i.e., sodium-chloride-
based electrolytes, on a titanium alloy. The study re-
vealed that the combination of sodium chloride and citric
acid achieves the greatest cross-section and roundness.
Better conicity were obtained from sodium chloride and
citric acid compared to the other electrolytes. The com-
bination of sodium chloride and glycerol gave a better
treated surface due to the chelating effect of glycerol.
Researchers enhanced the material removal rate and
overcut and only few have concentrated on evaluating
the corrosion and pitting on the machined surface. The
corrosion formation on the surface of the workpiece af-
fects the surface quality and weakens the metal, but it
also generates a bell mouth profile. Hence, in this re-
search an experiment is planned to evaluate the sur-
face-corrosion factor for the Hastelloy C-276.
2 EXPERIMENTAL PART
Figure 1 depicts the ECMM setup used for machin-
ing the workpiece of Hastelloy C-274. Table 1 presents
the composition of Hastelloy C-276. This alloy has ex-
cellent mechanical and corrosion resistance properties
and is used in high-temperature and high-pressure envi-
ronments. The electrode made of stainless steel is coated
with polytetrafluoroethylene (PTFE) to prevent electric
flux escaping from the circumference of the electrode.
1
The PTFE has good thermal and chemical inertness
along with electrical insulation characteristics. Figure 2
shows the tool coated with PTFE. The workpiece is
given with positive charges and the cathode is connected
with the negative charges and sodium nitrate electrolyte
(NaNO
3
) is used to bridge the two electrodes. The
NaNO
3
electrolyte is prepared using 1 liter of distilled
water and thoroughly mixed with different weights of
salts. The ECMM setup has basic elements for electro-
lyte recirculation, a tool forwarding attachment and a
pulsed supply system. The input parameters and levels
P. VENUGOPAL et al.: EFFECT OF ELECTROCHEMICAL PROCESS PARAMETERS ON THE HASTELLOY C-276 ALLOY ...
676 Materiali in tehnologije / Materials and technology 57 (2023) 6, 675–680
Table 1: Composition of Hastelloy C-276 (w/%)
7
Ni Cr Mo Fe W Mn Cu C Si Co V
57 balance 16 16 5 4 <1 0.5 <0.01  0.08  2.5  0.35
Table 2: Tabulated values of ECMM factors and performance measures
Expt. No
Voltage
(V)
Duty Cycle
(%)
Electrolyte Concen-
tration (g/L)
Machining Speed
(μm/sec)
Surface Corrosion
Factor
1 7 90 35 0.1583 1.1231
2 8 90 35 0.1759 1.0234
3 9 90 35 0.2111 0.9045
4 10 90 35 0.2879 1.0848
5 11 90 35 0.3725 1.0602
6 11 50 35 0.1624 1.1179
7 11 60 35 0.1979 1.0645
8 11 70 35 0.2111 1.0714
9 11 80 35 0.2639 1.0595
10 11 90 35 0.3167 1.0759
11 11 90 15 0.1583 1.1449
12 11 90 20 0.1810 1.1312
13 11 90 25 0.2262 1.0625
14 11 90 30 0.3167 1.0825
15 11 90 35 0.4222 1.0988
Table 3: Fixed parameters
Constant parameters Thickness of workpiece Electrode diameter Frequency Volume of Electrolyte
Values 380 μm 484 μm 50 Hz 1 L

are selected based on the previous experiments, i.e., volt-
age, duty cycle and electrolyte concentration and output
performances are machining speed and surface corrosion
factor.
11
Table 2 shows the parameters and levels and the
output performance. The machining speed is evaluated
by measuring the thickness of the workpiece using the
micrometer and dividing the same value using the ma-
chining time in seconds. The machining time is the time
taken to complete the micro-hole. The evolution of hy-
drogen bubbles beneath the workpiece from the electrode
ensures the completion of the micro-hole.
12
The surface
corrosion factor is measured using the optical micro-
scope image which is the ratio of Dmax to Dmin. Dmax
is the length of the surface with corrosion/pitting and
Dmin is the length of the micro-hole.
13
3 RESULTS
The effect of voltage on the machining speed and sur-
face-corrosion factor is shown in Figure 3. It can be per-
ceived from the graph that the machining speed increases
with voltage. The input is varied between 7 V and 11 V,
while the increase in voltage increases the electrochemi-
cal reaction. The increase in voltage enhances the current
density required for the machining. As per Faraday’s law
of electrolysis, the dissolution efficiency depends on the
applied voltage between the electrodes. The linear in-
crease in machining speed is witnessed for the range of
9 V to 11 V. At a higher voltage the migration of ions
from the anode is larger, attributed to a higher machining
speed. The migration of ions from the anode depends on
the electric potential and electric gradient. Moreover, the
formation of the double layer at the anode due to polar-
ization increases the dissolution.
14
The PTFE-coated
electrode prevents any stray current occurring at the cir-
cumference of the electrode and the anode and cathode
gap plays an important role in the dissolution process. If
the distance between the anode and cathode is shorter
than the double layer, the capacitance charging will be
quicker attributing for a highly localized dissolution.
The surface-corrosion factor decreases with an in-
crease in the voltage level and further increases, as pre-
sented in Figure 4. In the ECMM process, although the
tool electrode is coated with PTFE, the straying current
from the tool tip forms the surface pitting/corrosion on
the anode surface. For the parameter combination of 7 V,
90 % duty cycle, 35 g/L electrolyte concentration, the
surface-corrosion factor is 1.1231. At 90 % duty cycle
the pulse on time is on live for more time and stray cur-
P. VENUGOPAL et al.: EFFECT OF ELECTROCHEMICAL PROCESS PARAMETERS ON THE HASTELLOY C-276 ALLOY ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 675–680 677
Figure 1: ECMM Cell
Figure 4: Micro-hole with surface corrosion Figure 2: PTFE-coated tool
Figure 3: Voltage vs machining speed and surface-corrosion factor

rent flux from the tip creates the surface corrosion on the
top surface of the workpiece. Figure 5 shows the mi-
cro-hole with the surface corrosion/pitting. The surface
pitting arises due to the formation of a localized electro-
chemical cell on the surface of the Hastelloy C-276. The
localized electrochemical cell will split into anodic and
cathodic zones in which the breaking of the oxide layer
and the underlying metal act as an anode and surface of
the hastelloy C-276 act as a cathode.
15
This phenomenon
leads to the formation of pits on the micro-hole circum-
ference. The clusters of pits are shown in Figure 6.The
formation of tiny pits is caused by the repetitive electric
force, and collapsing of hydrogen bubbles in the machin-
ing area. The hydrogen bubbles are evolved by the cath-
ode during the electrolysis.
The effect of duty cycle on the machining speed and
surface-corrosion factor is depicted in Figure 7. The ma-
chining speed shows an increasing trend with an increase
in the duty cycle. The linear increase in machining speed
is witnessed for the duty cycle range of 70 % to 80 %.
The duty cycle is the ratio of the pulse-on time to the to-
tal time (Pulse-on time + Pulse-off time) and the 70 %
duty cycle contributes a good quantity of the current den-
sity required for machining. A further increase in the
duty cycle to 90 % the pulse-off time reduces and the
pulse-on time increases to the maximum value, and this
high duration of pulse-on current in the electrode attrib-
utes for the high machining speed.
The surface-corrosion factor is found to decrease
with the increase in the duty cycle. At 11 V, 50 % duty
cycle, 35 g/L electrolyte concentration the surface-corro-
sion factor is high due to the longer pulse-off time. Dur-
ing the lower duty cycle the pulse-on time is less and
more time is required for machining. Hence, at a lower
duty cycle the surface corrosion is 1.1179 and further re-
duces to 1.0645 for 60 % duty cycle. At 11 V, 90 % duty
cycle and 35 g/L electrolyte concentration the sur-
face-corrosion factor is less due to the fact at higher level
of input parameters the dissolution rate is faster and
hence the workpiece-surface exposure time to the stray
current is less, leading to less corrosion/pitting on the
circumference of the hole, as shown in Figure 8.
The effect of electrolyte concentration on the ma-
chining speed and surface-corrosion factor is shown in
Figure 9. For machining the Hastelloy C-276, the passi-
vating electrolyte NaNO
3
is used. The formation of cor-
rosion/pitting on the surface of the workpiece depends
on the stray current from the electrode. In the ECMM
machining process the current density depends on the
conductivity of the electrolyte and the intensity of the
P. VENUGOPAL et al.: EFFECT OF ELECTROCHEMICAL PROCESS PARAMETERS ON THE HASTELLOY C-276 ALLOY ...
678 Materiali in tehnologije / Materials and technology 57 (2023) 6, 675–680
Figure 8: Micro-hole with less corrosion/pitting
Figure 6: Micro-hole surface with cluster of corrosion/pitting
Figure 7: Duty cycle vs machining speed and surface-corrosion factor
Figure 9: Electrolyte concentration vs machining speed and sur-
face-corrosion factor

electric field.
16
The electrical conductivity again depends
on the temperature of the electrolyte and quantity of dis-
solution product in the electrolyte. At 11 V, 90 % duty
cycle and 15 g/L of electrolyte concentration the number
of ions in 1 litre of distilled water is responsible for less
removal of material from the workpiece. A further pro-
gressive increase in electrolyte concentration increases
the machining rate, as depicted in Figure 9. The machin-
ing speed linearly increases with electrolyte concentra-
tion range of 25 g/L to 35 g/L. The surface corrosion fac-
tor found to 1.1449 for the experiment combination, i.e.,
11 V, 90% duty cycle, 15 g/L. A further increase in the
electrolyte concentration from 25 g/L to 35 g/L the sur-
face corrosion is found to be 1.0625, 1.0825 and 1.0988,
respectively, which is less than the electrolyte concentra-
tion range of 15 g/L to 20 g/L. The generation of the re-
action product will be high at a higher concentration of
electrolytes and moreover the bursting of gas bubbles di-
minishes the stray current pitting. Figure 10 shows the
micro-hole with un-flushed debris. The proper flushing
of debris ensures good quality in the ECMM.
Figure 11 shows the surface profilograph of the cor-
rosion-affected zone. The surface roughness depth pro-
file shown in Figure 12 depicts the values of Rz, Rt, Ra
as 16.3 μm, 99.1 μm and 1.90 μm, respectively, and on
repeating the same the lowest surface roughness was ob-
tained as 15.4 μm, 50.6 μm and 1.49 μm. The 3D surface
file shown in Figure 13 shows the surface roughness val-
ues of 0.844 mm, 0.844 mm and 176 μm along the X, Y
and Z directions.
P. VENUGOPAL et al.: EFFECT OF ELECTROCHEMICAL PROCESS PARAMETERS ON THE HASTELLOY C-276 ALLOY ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 675–680 679
Figure 10: Micro hole with unflashed debris
Figure 13: 3D surface profile of the corrosion-affected zone Figure 11: Surface profile graph of corrosion zone
Figure 12: Depth profile of the corrosion-affected surface

4 CONCLUSIONS
The PTFE-coated electrode is used in ECMM to un-
derstand the effect of the process parameters on the ma-
chining speed and the surface-corrosion factor. The ef-
fect of voltage, duty cycle and electrolyte concentration
on the above was studied. The voltage range of 9–11 V
has an impact on the machining speed. The surface cor-
rosion was found to be 1.1231, which is the third-highest
value for the parameter combination of 7 V, 90 % duty
cycle and 35 g/L electrolyte concentration. The sur-
face-corrosion factor decreases with an increase in the
voltage. Among the conducted experiments, the 9 V, 90
% duty cycle, 35g/L combination shows lowest sur-
face-corrosion factor of 0.9045. The duty-cycle range of
70–90 % has an influence on the machining speed. The
electrolyte concentration range of 25–35 g/L shows a lin-
ear increase in the machining speed and the surface-cor-
rosion factor is found to be highest of 1.1449 and second
highest of 1.1312 for the electrolyte concentrations of 15
g/L and 20 g/L, respectively. The surface-roughness,
depth-profile values of Rz, Rt, Ra for the corrosion-af-
fected zone are 5.4 μm, 50.6 μm and 1.49 μm.
5 REFERENCES
1
P. Venugopal, T. G. Arul, R. Thanigaivelan, Performance optimiza-
tion of a PTFE-coated electrode in electrochemical micromachining.
Ionics, 28 (2022) 10, 4745–4753, doi:10.1007/s11581-022-04686-1
2
J. R.Vinod Kumaar, R. Thanigaivelan, M. Soundarrajan, A perfor-
mance study of electrochemical micro-machining on SS 316L using
suspended copper metal powder along with stirring effect. Mater.
Manuf. Process., 37 (2022) 13, 1526–1539, doi:10.1080/10426914.
2022.2030874
3
V. Palaniswamy, K. Seeniappan, T. Rajasekaran, N. Lakshmaiya, En-
hancing MRR and accuracy with magnetized graphite tool in electro-
chemical micromachining of copper, Chem. Ind. Chem. Eng. Q., 29
(2023) 3, 201–208, doi:10.2298/CICEQ220731027P
4
N. Rajan, R. Thanigaivelan, K. G. Muthurajan, Machinability studies
on an Al7075 composite with varying amounts of B4C using an in-
duction-heated electrolyte in electrochemical machining, Mater.
Tehnol., 53 (2019) 6, 873–880,doi: :10.17222/mit.2019.077
5
R. Thanigaivelan, R. Senthilkumar, R. M. Arunachalam, N.Nata-
rajan, Impact of the shape of electrode-tool on radical overcut of mi-
cro-hole in electrochemical micromachining, Surf. Eng. Appl.
Electrochem., 53 (2017), 486–492, doi:10.3103/
S1068375517050143
6
G. Kumarasamy, P. Lakshmanan, G. Thangamani, Electrochemical
micromachining of hastelloy C276 by different electrolyte solutions,
Arab J Sci Eng., 46 (2021), 2243–2259, doi:10.1007/s13369-
020-05032-1
7
D. Panigrahi, S. Rout, S. K. Patel, D. Dhupal, Stray current and its
consequences on microstructure of Hastelloy C-276 during paramet-
ric investigation on geometrical features: fabricated by electrochemi-
cal micromachining, Int. J. Adv. Manuf. Technol., 112 (2021),
133–156, doi:10.1007/s00170-020-06365-9
8
R. Gobinath, P. Hariharan, B. M. Prasanth,Electrochemical Micro-
machining of Hastelloy Using Cu–NaBr Nanoparticles Mixed Elec-
trolyte, Russ J Appl Chem, 95 (2022) 9, 1427–1437, doi:10.1134/
S1070427222090191
9
S. Liu, G. Thangamani, M. Thangaraj, P. Karmiris-Obratañski, Re-
cent trends on electro chemical machining process of metallic mate-
rials: a review, Archiv.Civ.Mech.Eng, 23 (2023) 3, 158,
doi:10.1007/s43452-023-00703-w
10
G. Thangamani, M. Thangaraj, K. Moiduddin, S. H. Mian, H. Alkha-
lefah, U. Umer, Performance analysis of electrochemical micro ma-
chining of titanium (Ti-6Al-4V) alloy under different electrolytes
concentrations, Metals, 11(2021) 2, 247, doi:10.3390/met11020247
11
K. G. Saravanan, R. Thanigaivelan, M. Soundarrajan, Comparison of
electrochemical micromachining performance using TOPSIS,
VIKOR and GRA for magnetic field and UV rays heated electrolyte,
Bull. Pol. Acad. Sci. Tech. Sci., 69 (2021) 5, e138816, doi:10.24425/
bpasts.2021.138816
12
R. Thanigaivelan, R. M. Arunachalam, J. Jerald, T. Niranjan, Appli-
cations of Taguchi technique with fuzzy logic to optimise an electro-
chemical micromachining process, International Journal of Experi-
mental Design and Process Optimisation, 2 (2011) 4, 283–298,
doi:10.1504/IJEDPO.2011.043565
13
Bikash Ranjan Moharana, Kasinath Das Mohapatra, Kamalakanta
Muduli, Dillip Kumar Biswal, Tapas Kumar Moharana, Multi-re-
sponse optimisation of machining parameters in WEDM using hy-
brid desirability-based TOPSIS concept, 14 (2023) 4, 439–459,
doi:10.1504/IJPMB.2023.132214
14
N. Sato, Interfacial ion-selective diffusion layer and passivation of
metal anodes, Electrochim. Acta, 41 (1996) 9, 1525–1532
doi:10.1016/0013-4686(95)00404-1
15
S. Guo, D. Xu, Y. Li, Y. Guo, S. Wang, D. D. Macdonald, Corrosion
characteristics and mechanisms of typical Ni-based corrosion-resis-
tant alloys in sub-and supercritical water, J. Supercrit. Fluids, 170
(2021), 105138, doi:10.1016/j.supflu.2020.105138
16
G. S. Was, Corrosion and stress corrosion cracking fundamentals.
Fundamentals of Radiation Materials Science: Metals and Alloys,
2
nd
ed., Springer New York, NY 2017, 857–949, doi:10.1007/978-1-
4939-3438-6
P. VENUGOPAL et al.: EFFECT OF ELECTROCHEMICAL PROCESS PARAMETERS ON THE HASTELLOY C-276 ALLOY ...
680 Materiali in tehnologije / Materials and technology 57 (2023) 6, 675–680