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Chander Prakash
Department of Mechanical Engineering,
UIET, South Campus,
Panjab University,
Sector-25,
Chandigarh 160014, India
e-mail: chander.mechengg@gmail.com
H. K. Kansal
Department of Mechanical Engineering,
UIET, South Campus,
Panjab University,
Sector-25,
Chandigarh 160014, India
e-mail: shaarut@yahoo.com
B. S. Pabla
Department of Mechanical Engineering,
National Institute of Technical Teachers
Training & Research, NITTTR,
Sector-26,
Chandigarh 160019, India
e-mail: bsp@nitttrchd.ac.in
Sanjeev Puri
Center for Stem Cell and Tissue Engineering,
Panjab University,
Sector-14,
Chandigarh 160014, India;
Department of Biotechnology,
UIET, South Campus,
Panjab University,
Sector-25,
Chandigarh 160014, India
e-mail: spuri_1111@yahoo.com
Powder Mixed Electric Discharge
Machining: An Innovative
Surface Modification Technique
to Enhance Fatigue Performance
and Bioactivity of b-Ti Implant
for Orthopedics Application
The development of surface modification technique has been the subject of the studies
regarding the fatigue performance and biological characterization of the modified layers.
In the present research work, powder mixed electric discharge machining (PMEDM) a
novel nonconventional machining technique has been proposed for surface modification
of b-Ti implant for orthopedics application. The surface topography and morphology like
roughness, surface cracks, and recast layer thickness of each of the machined specimens
were investigated using Mitutoyo surface roughness tester and field-emission scanning
electron microscopy (FE-SEM), respectively. This study aims to investigate the effect of
surface characteristics of PMEDM process on the fatigue performance and bioactivity of
b-Ti implants and moreover a comparative analysis is made on the fatigue performance
and biological activity of specimens machined with presently used machining methods
like electric discharge machining (EDM) and mechanical polishing. The high cycle fa-
tigue (HCF) performance of polished specimens was superior and had no adverse effect
of microstructure on fatigue endurance. As expected, the fatigue behavior of b-Ti
implant-based alloy, after undergoing EDM treatment, is poorly observed due to the mi-
crorough surface. The fatigue performance is dependent on microstructure and surface
roughness of the specimens. Subsequent PMEDM process significantly improves the fa-
tigue endurance of b-Ti implant-based alloy specimens. PMEDMed surface with micro-,
sub-micro-, and nano-structured topography exhibited excellent bioactivity and improved
biocompatibility. PMEDMed surface enabled better adhesion and growth of MG-63
when compared with the polished and EDMed substrate. Furthermore, the differentiation
results indicated that a combination of nanoscale featured submicrorough PMEDMed
surface promotes various osteoblast differentiation activities like alkaline phosphatase
(ALP) activity, osteocalcin production, the local factor osteoprotegerin, which inhibits
osteoclastogenesis. [DOI: 10.1115/1.4033901]
Keywords: b-phase titanium alloy, powder mixed EDM, surface roughness, biocompati-
bility, fatigue, Mg-63 cell, in vitro analysis
Introduction
The demand for total joint replacement is increased rapidly and
a major achievement of orthopedic surgery is to improve the qual-
ity of life and longevity of human being [1]. In total joint replace-
ment, the artificial organ is used for restoring the functionality of
a dysfunction natural organ or tissue of the body [2]. Mechanical
biocompatibility is the prime requirement for orthopedics implant
where the implant material should possess a low Young’s modu-
lus (near to cortical bone 10–30 GPa) to prevent stress-shielding
effects but must maintain mechanical properties such as high fa-
tigue strength [3]. Ti and its alloys are used as a substitute for
human hard tissue replacements due to their superior biocompati-
bility and excellent mechanical properties [4]. Although they grat-
ify most of the requirements of implant material, they fail to meet
the requirements of osseointegration that involves efficient bind-
ing to surrounding tissues because of their inactive surface
characteristics, low surface hardness, and poor wear resistance
[5]. This can lead to problems such as bone resorption and implant
loosening in long-term performance. There, it is necessary to
modify the surface of the implant for better stability and fixation
of the implant [6]. Thus, present research scenario focused on the
development of better surface treatment technologies, which can
fabricate biocompatible surface to enhance bioactivity as well as
mechanical properties of bulk in single operation [7]. Accord-
ingly, a number of methods/techniques have been proposed and
used to modify the surface of Ti-based implants to enhance for
improving its mechanical, chemical, and biological properties,
and wear and corrosion resistance [8]. However, such surface
treatments sometimes induced a harmful effect over a long dura-
tion due to poor adhesion and low physical bond strength at the
interface [9]. Thus, this gained a scientific interest in the research
and development of new surface modification/treatment methods
to improve the biocompatibility wear and corrosion resistance of
Ti-based implants in single machining operation.
Recently, Prakash et al. have critically reported that EDM has
been widely used in the past for surface modification of Ti-based
implants to improve their biocompatibility, wear resistance,
Contributed by the Computers and Information Division of ASME for publication
in the JOURNAL OF COMPUTING AND INFORMATION SCIENCE IN ENGINEERING. Manuscript
received January 29, 2016; final manuscript received June 11, 2016; published online
November 7, 2016. Assoc. Editor: Giorgio Colombo.
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corrosion resistance and surface hardness [10]. EDM not only
modifies the surface of Ti-6Al4V alloy, but also it converts the
surface into biocompatible layer of nanohydrides, which has
favorable impact on cell attachment, and provide a vehicle for cell
growth and proliferation [11–13]. The capability of EDM to
enhance the surface hardness, wear resistance, corrosion resist-
ance, and bioactivity of Ti-6Al4V alloy by surface alloying has
been reported by Bin et al. [14]. Conversely, Harcuba et al.
reported in his research that EDMed surface promotes cell adhe-
sion on Ti-6Al4V alloy, but high surface roughness and crack
density reduced the fatigue performance which results in clinical
failure [15]. Further, his coauthor reported in their research that
fatigue endurance of Ti-6Al4V alloy was severely affected by sur-
face topography [16]. It was also reported that the fatigue per-
formance of EDMed specimens can be improved by heat
treatment methods followed by EDM process. In order to improve
the bioactivity and fatigue performance of Ti-6Al-4V alloy, a
three-step mechanical treatment involving a combination of con-
ventional machining processes (shot peening and chemical
milling) followed by EDM has been attempted [17,18]. Apart
from surface topography, surface composition and chemistry play
an important role in fatigue endurance [19]. Guo et al. investi-
gated the effect of TiN formation by EDM on fatigue performance
of AISI D2 steel and it was observed that TiN has a positive effect
in improving the fatigue life of tool steel [20,21]. Tia et al.
reported that the fatigue performance of EDMed component can
be improved by reducing surface crack density in recast layer
[22]. Further, the fatigue performance of EDMed specimens was
improved by wire brushing followed by polishing.
EDM is an electrothermal machining process, which generates
a large number of electrical sparks in a fraction of seconds and
produces intense heat which removes material from workpiece
surface [23]. As a result, a number of surface defects like high sur-
face roughness, high surface crack density, and macrosize pit/
dimples were formed on the machined surface which deteriorate
the surface quality [24,25]. This poor surface quality degraded
the fatigue performance [26], corrosion performance [27], of the
implant, and as a result, bone-implant interface failure.
In the past, a number of advancements in EDM process such as
ultrasonic vibration assisted EDM [28], rotary assisted EDM [29],
magnetic assisted EDM [30], electro discharge coating [31], and
PMEDM [32–40] have been attempted by many researchers to
prevent the formation of surface defects like micro-cracks, high
roughness, and thick recast layer. Among these, PMEDM is con-
sidered the most promising approach to improve the quality of the
surface and reduce the number of surface cracks [23,41]. Wong
et al. was the first to explore the capability of PMEDM for gener-
ating near-mirrorlike finishing [42]. Further, Pecas et al. reported
the process polishing capability of AISI-D2 steel by PMEDM
[43]. Prabhu et al. reported that the surface roughness of the work-
piece was achieved up to nanolevel by an EDM process using
multiwall carbon nanotubes as dielectric solvent [44]. Recently,
the application of PMEDM using carbon nanotubes as additives
has generated interest and has been increasingly used for nanofin-
ishing of substrates [45].
Prakash et al. have been reported the potential of PMEDM to
enhance the surface microhardness, corrosion resistance, and bio-
activity of b-Ti implants used for orthopedic applications [46].
Ekmekci et al. proposed the application of PMEDM to deposit the
biocompatible layer of hydroxyapatite powder on Ti-6Al-4V alloy
Table 1 Chemical composition of b-Ti implant alloy
Elements Titanium
(Ti)
Niobium
(Nb)
Tantalum
(Ta)
Zirconium
(Zr)
Weight
percentage (%)
Balance 35 7 5
Table 2 Properties of b-Ti implant compared to human bone
Properties b-Ti alloy Human bone
Hardness 380 Hv —
Density (kg/m
3
) 5700 2000
Elastic modulus (GPa) 55 15–20
Strength (MPa) 560–950 150
Poisson’s ratio 0.33 0.3
Melting point (C) 1765 —
Coefficient of expansion (10
6
C
1
) 9.03 —
Fig. 1 (a) EDM machine; (b) and (c) experimental setup of PMEDM
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for medical applications [47]. The application of PMEDM to
modify the surface of b-Ti alloy to improve the wear and tribolog-
ical performance for biomedical implants has been reported [48].
Recently, Prakash et al. optimized the process parameters of
PMEDM for fabrication of biocompatible layer on b-Ti alloy
using NSGA-II coupled with Taguchi based response surface
methodology and it was also found that the surface cracks
and recast layer thickness can be controlled by PMEDM process
[49].
This creates an opportunity to utilize the advantages of
PMEDM for finishing purposes. In the present research work, sur-
face modification of b-Ti implant has been carried out in order to
improve the fatigue endurance of EDMed components. Since
PMEDM technique has still not been attempted in the surface
Fig. 2 100 KN UTM machine for tensile and fatigue testing
Fig. 3 (a) Microstructure, (b) SEM micrographs, (c) EDS spectrum, and (d) XRD pattern of unmachined b-Ti alloy
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treatment of b-Ti-based implants, no report on fatigue perform-
ance can be indexed up to present. The machined surface topogra-
phy, composition, and hardness were first characterized by
various surface characterization techniques and then, in-depth a
critical investigation of fatigue performance and in vitro bioactiv-
ity of the b-Ti implant has been carried out.
Materials and Methods
Sample Preparation. The b-phase Ti alloy was chosen as
implant material and composition of it is shown in Table 1. The
b-Ti alloy was cast using the facility available at DRDO-DMRL,
India with a mixture of titanium (Ti) along with niobium (Nb),
tantalum (Ta), and zirconium (Zr) powder as raw materials. The
Ti–35Nb–7Ta–5Zr (TNTZ) alloy was prepared using vacuum arc
melting technique to obtain compact and homogeneous ingots
with neither weight loss nor oxidation. The mechanical and physi-
cal properties were shown in Table 2. For microstructure measure-
ments, the test specimens were mirror polished using adequate
polishing methods and then samples were etched with a Kroll’s re-
agent (10 vol. % HF and 5 vol. % HNO
3
and rest water) for
approximately 15 s. The microstructures were observed by optical
microscope and FE-SEM made of JEOL model-7600 F. The
Fig. 4 Stress–strain tensile curve of the b-Ti alloy
Table 3 Mechanical properties of different Ti alloys
Material H(GPa) E(GPa) r
max
(MPa) r
0.2
(MPa) e(%) r
limit
(MPa) N(Lacs)
Ti35Nb7Ta5Zr 10.6 55 590 565 13 250 30
Ti29Nb4.6Zr13Ta 2 63 500 300 — — —
Ti6Al4V — 110 860–965 795–869 6–15 200 >50
H—microhardness; E—elastic modulus; r
max
—tensile strength; r
0.2
—yield strength; e—elongation; r
limit
—fatigue limit; N—number of cycles to failure
Fig. 5 SEM images of (a) and (b) EDM-machined and (c) and (d) PMEDM-machined b-Ti alloy
specimens
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composition of as prepared cast b-phase Ti alloy was analyzed by
energy-dispersive X-ray spectroscopy (EDS) and X-ray diffrac-
tion (XRD) technique.
Surface Modification Using PMEDM. A new experimental
system for PMEDM was fabricated and experiments are per-
formed on die-sinking EDM machine (model SZNC-35-5030)
made by Sparkonix (India) Pvt. Ltd., Pune as can be seen in Fig. 1
[23]. Pure silicon powder (99.7 wt.%) with a particle size
of <35 lm has been mixed into the dielectric fluid of EDM. The
optimized experimental conditions and process parameters
employed for PMEDM as a process for surface modification are
peak current 5 A, pulse duration 5 ls, duty cycle (8%), and 4 g/l
silicon powder concentration [49]. After machining, the machined
surface morphology of specimens was analyzed by FE-SEM and
the surface roughness was measured using Mitutoyo surface
roughness tester.
Tensile Testing and HCF Testing. In the present study, tensile
tests and HCF were conducted on 100 KN universal testing
machine (UTM) made of Bangalore Integrated System Solutions
(BISS) a unit of unit of Illinois Tool Works (ITW) USA. The axial
UTM utilized in this testing is shown in Fig. 2. All specimens
were fabricated according to the recommended dimensions con-
sistent with ASTM Standard E8-04 (for tensile testing) and E466-
07 (for HCF testing), respectively. Tensile tests were conducted
on 100 KN (UTM, BIS) with a strain rate of 10
4
s
1
.To
investigate the influence of the surface roughness on the fatigue
performance for all of the materials, the specimens were subjected
to different surface modification techniques—PMEDM, EDM,
and polishing. The HCF tests were conducted with force control
using a sinusoidal waveform at a frequency of 50 Hz. The stress
ratios (R) were equal to 0.1. For the potential application in ortho-
pedics, fatigue life strength was measured and the number of
cycles to failure was recorded at complete fracture of the speci-
mens. A criterion of infinite life of 10
7
cycles was also adopted.
To obtain stress-number (S–N) curves, only specimens with dam-
age within the gauge length were used. After fatigue test, the frac-
tography of failed specimens was analyzed using FE-SEM.
Cell Culture and Assays. MG-63 human osteoblastlike cells
were utilized to evaluate the bioactivity of machined specimens.
Mg-63 cells were cultured as per the procedure adopted in previ-
ous research [11,46]. The confluent cells were seeded and cultured
on control surface and machined samples of b-Ti alloy plates at a
cell density of 1 10
5
cells/cm
2
. At given time points, the cul-
tured samples were fixed with 2.5% glutaraldehyde and dried for
24 hrs in a desiccator before gold sputtering for FE-SEM analysis
of the samples. Cell proliferation was evaluated using MTT assay
and Deoxyribonucleic acid (DNA) content [12–13]. For cell dif-
ferentiation, Alkaline Phosphatase activity (ALP), osteocalcin and
Osteoprotegerin activity assays were performed after 24 hrs of cell
culture.
Results and Discussion
Microstructure, Composition, and Mechanical Properties.
Figure 3shows the optical image, SEM image, EDS spectrum,
and XRD pattern of the polished (unmachined) surface. The
microstructure of b-Ti alloy has been also seen in Fig. 3(a). The b
grain boundary pattern can be observed. As observed, the polished
surface displayed a relatively smooth surface featuring polishing
grooves only (Fig. 3(b)). Figure 3(c)shows the EDS spectra of
b-Ti alloy in one of the investigated area and analysis confirmed
the presence of Ti, Nb, Ta, and Zr. To better understand the phase
composition of the investigated alloy, XRD structural analysis
was performed. The XRD pattern (Fig. 3(d)) revealed the presence
of a0phase (Ti), together with bbcc phase (Nb, Ta, and Zr) weak
peaks, partially overlapped on a0peaks.
The stress versus strain curve obtained from tensile tests of the
b-Ti alloy is presented in Fig. 4. The mechanical properties of the
b-Ti alloy in comparison to other titanium alloys used in biomedi-
cal applications are also given in Table 3. The Young’s modulus
and ultimate tensile strength of b-Ti alloy is 55GPa and 590MPa,
respectively. The b-Ti alloy has high elongation compared to
Fig. 6 Cross section SEM micrograph of (a) EDMed surface and (b) PMEDMed surface
Fig. 7 Surface roughness parameters of the polished, EDMed,
and PMEDMed b-Ti alloy
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Ti-6Al-4 V, but still in the range adequate for biomedical applica-
tions, according to Niinomi [3].
Machined Surface Topography Analysis. Figure 5shows the
SEM micrograph of b-Ti implant surface after EDMed and
PMEDMed at optimized conditions. The evidence of redeposited
molten metal, globules, macro scale craters, microcracks, and
pockmarks has been identified on the EDMed surface. During
EDM, the specific width and length of surface cracks, ridges of
redeposited molten metal, and discharge craters were formed. The
surface Poor surface quality was clearly evidenced from the
EDMed surface. This is because with an increase in pulse current,
the generated discharge energy increases, which melts more mate-
rial from workpiece surface in the form of debris. These debris
cannot flush out and deposited on the periphery of the craters,
allowing spherical coarse grains growth and hence responsible for
high ridges of redeposited molten metal (Fig. 5(b)). Figures 5(c)
and 5(d)show the SEM micrograph of b-Ti implant surface after
PMEDM. As compared to EDM, PMEDM provides smooth sur-
face morphology and interconnected discharge craters with
reduced size. It can be clearly seen that the ridges of redeposited
molten metal become flat and interconnected. A crack-free very
smooth surface was obtained. It can be seen that the microscopic
crater/pit size was in the 15–20 lm range on the surface of the
PMEDM-machined surface. This is because with the addition of
powder particles, the discharge gap increases, which initiate more
spark locations and frequency. As a result, the generated thermal
energy decreases and materials are removed in the form of micro-
debris with small crater size from the workpiece surface. This
eroded debris can flush out easily due to large discharge gap,
which enhances the surface finish and material removal rate [43].
Recast Layer Thickness. The PMEDM has very significant
effect on recast layer (RLT). Figure 6shows the cross section
SEM micrograph of RLT after EDM and PMEDM. The EDMed
surface consists mainly of resolidified drops of the material. The
thickness of recast layers on the EDMed surface has been meas-
ured around 9–10 lm (Fig. 6(a)). The resolidified material has
poor bonding and is loosely connected; thus, there is a risk of their
loosening. These particles may cause considerable danger since
they can penetrate between articulating parts of the joint and dam-
age them. This means that lower the recast layer thickness, lower
Fig. 8 (a)S–N curve of fatigue tests for polished, EDMed, and
PMEDMed b-Ti alloy
Fig. 9 Attachment of MG-63 cells on (a) polished, (b) EDMed, and (c) PMEDMed surface, and
(d) MTT assay of MG-63 cells after culture for 1, 3, and 7 days
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will be the surface defects availability. On the other hand,
PMEDMed surface has thin recast layer as compared to EDMed
surface. The thickness of recast layers on the PMEDMed surface
at dielectric mixed with 4 g/l concentration of Si powder has been
measured around 2lm. The loose surface particles are not
observed on the surface after PMEDM treatment (Fig. 6(b)). The
surface roughness is significantly lower and free from cracks or
defects.
Surface Roughness. Surface roughness plays important roles
in the stability of an implant. Microscale surface roughness pro-
motes cell attachment and proliferation [18]. It has been found
that the low surface roughness has a positive effect on the fatigue
performance [16,17]. The surface roughness was measured in dif-
ferent parameters, i.e., average roughness (Ra), root-mean-square
roughness (Rq), and mean roughness depth (Rz) for the polished,
EDMed, and PMEDM-machined surfaces of the b-Ti alloy are
shown in Fig. 7. The lowest surface roughness is obtained by the
polishing process (Ra ¼0.111 lm, Rq ¼0.167, and Rz ¼0.87 lm).
The EDM generates high surface roughness comparatively to pol-
ishing (Ra ¼1.38 lm, Rq ¼2.07, and Rz ¼10.9 lm). PMEDM
generates effectively less roughness compared to EDMed surfaces
(Ra ¼0.72, Rq ¼1.08 lm, and Rz ¼5.68 lm).
HCF Endurance. The fatigue endurance of test specimens was
evaluated using HCF performance. Figure 8shows the S–N curves
of polished, EDMed and PMEDMed samples. The mechanically
polished samples have no adverse effect on fatigue endurance and
high fatigue strength. The EDM-treated specimens have poor fa-
tigue performance (fatigue endurance limit of only 150 MPa) and
are insufficient for applications in orthopedics, as reported
previously [15,16,]. EDM-treated surface composed of surface
defects like thick recast layer, has high surface roughness, and
high surface crack density. Poor fatigue performance is attributed
to the strong notch effect due to high surface roughness and
microcracks on the EDMed surface. On the other hand, PMEDM-
treated specimens have improved fatigue performance as com-
pared to EDMed specimens. This improvement in fatigue per-
formance is attributed due to the reduction of surface roughness,
microsurface cracks, and recast layer thickness, which suppresses
the adverse notch effect. Since the recast layer and surface rough-
ness were successfully reduced by PMEDM technique on the
machined surface, a crack-free surface can be obtained using
PMEDM process. Achieved fatigue endurance limit of 250 MPa is
sufficient for intended applications.
In-Vitro Analysis. The bioactivity of the unmachined, EDMed,
and PMEDM-machined samples of b-phase Ti alloy has been
evaluated in terms of cell attachment, proliferation, differentiation
of MG-63 human osteoblastlike cells. The SEM micrographs
showed cell attachment and spreading on unmachined, EDMed,
and PMEDMed specimens (Fig. 9). The osteoblast cells showed
excellent tolerance to PMEDMed surface and cell morphology in
all groups has been normal and healthy. It has been noted that the
cells have been polygonal in shape and had many biological activ-
ities like cytoplasmic extensions, retraction of filopodia, and redi-
rection of extracellular matrix indicating the cell spreading on the
specimen’s surfaces. The PMEDM-treated surface shows higher
and tightly attachment of MG-63 cells and more biological activi-
ties as compared to the untreated and EDM-treated surface of the
b-Ti alloy. This indicates PMEDMed surface has a significant
impact on cell growth and metabolic activity, thus surface modify
by PMEDM to be proved as nontoxic and biocompatible. These
Fig. 10 Cell proliferation and differentiation results (a) DNA content, (b) ALP activity, (c)
osteocalcin, and (d) osteoprotegerin at 24 hrs of cell culture
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results have been corroborative with the previous findings in
which EDM has been used as surface treatment method
[11,16–17]. Metabolic activity and proliferation of osteoblastlike
cells (MG-63) have been measured through MTT test after cell
culture for 1, 3, and 7 days. Figure 9(d)illustrates the cell prolifer-
ation behaviors of osteoblastlike cells on unmachined, EDMed,
and PMEDMed surfaces of b-phase Ti alloy according to the
MTT assay. It can be observed that the PMEDM-treated surface
has high cell proliferation as compared to untreated and EDM-
treated of the b-Ti alloy. The PMEDM surface created a hydro-
philic surface, which enhances its bioactivity and biocompatibility
and, as a result, increased cell attachment and proliferation.
Higher Osteoblast differentiation activities were noticed on the
micro-, submicron-scale rough nanofeatured surface (Fig. 10).
These results are in good agreement with previous research find-
ings, which have indicated that a combination of nanoscale fea-
tures and submicron scale roughness is required to achieve good
cell adhesion, proliferation and cell growth, and osteoblast differ-
entiation. In the present study, ALP activity and osteocalcin pro-
duction activities were noticed on submicron-rough nanofeatured
surface at higher scale. The local factor osteoprotegerin, which
inhibits osteoclastogenesis, was also found increased on the
PMEDMed surface. These all results suggest that PMEDM treat-
ment tailored nanoscaled and microscaled surface features to pro-
mote biomechanical anchorage with the surface as well as in the
surrounding tissue. Based on the cell attachment, MTT assay, and
osteoblast differentiation results, it is evident that the PMEDM-
machined surface provides a wide range of dimensions for extrac-
ellular proteins anchoring and subsequent cell attachment, spread-
ing as well as proliferation.
Conclusions. In the present study, fatigue performance and cell
attachment and proliferation on b-phase Ti alloy were investigated
after surface treatment by polishing, EDM, and PMEDM. The
following conclusions are drawn from this investigation:
(1) PMEDM significantly improved the surface quality by
reducing surface defects like microcracks, surface rough-
ness, craters/pit size, recast layer thickness
(2) A very smooth and crack-free surface can be archived by
PMEDM. PMEDM significantly reduced the thickness of
recast layer. A very thin layer of 2lm was obtained
during PMEDM machining.
(3) Fatigue performance of PMEDM-treated specimen is
significantly improved. The fatigue endurance limit is
280 MPa, which is sufficient for the applications in
orthopedics.
(4) Surface topography and micro- and submicron-scale rough-
ness, which conferred bioactivity and biocompatibility of
b-phase Ti alloy. PMEDMed surface has promoted cell
adhesion and proliferation.
(5) Overall, PMEDM has the potential to enhance the mechani-
cal properties and enhances the osteoblast response. The
modified surface provides a promising range of application
in orthopedics.
Acknowledgment
Authors also gratefully thank Dr. Amit Bhattacharjee, Scientist-
F, Defence Metallurgical and Research Laboratories (DMRL),
DRDO-Hyderabad, India for providing material for research work.
This work was financially supported by Department of Science
and Technology (DST), Government of India under the Science
and Engineering Research Board scheme (Project No. SR/S3/
MERC/0028/2012).
References
[1] Geetha, M., Singh, A. K., Asokamani, R., and Gogia, A. K., 2009, “Ti Based
Biomaterials, the Ultimate Choice for Orthopaedic Implants-A Review,” Prog.
Mater. Sci.,54(3), pp. 397–425.
[2] Niinomi, M., 2009, “Recent Research and Development in Titanium Alloys for
Biomedical Applications and Healthcare Goods,” Sci. Technol. Adv. Mater.,
4(5), pp. 445–454.
[3] Niinomi, M., 1998, “Mechanical Properties of Biomedical Titanium Alloy,”
Mater. Sci. Eng.: A,243(1–2), pp. 231–236.
[4] Niinomi, M., Nakai, M., and Hieda, J., 2012, “Development of New Metallic
Alloys for Biomedical Applications,” Acta Biomater.,8(11), pp. 3888–3903.
[5] Liu, X. B., Meng, X. J., Liu, H. Q., Shi, G. L., Wu, S. H., Sun, C. F., Wang, M.
D., and Qi, L. H., 2014, “Development and Characterization of Laser Clad
High Temperature Self-Lubricating Wear Resistant Composite Coatings on
Ti–6Al–4V Alloy,” Mater. Des.,55, pp. 404–409.
[6] Minagar, S., Berndt, C. C., Wang, J., Ivanova, E., and Wen, C., 2012, “A
Review of the Application of Anodization for the Fabrication of Nanotubes on
Metal Implant Surfaces,” Acta Biomater.,8(8), pp. 2875–2888.
[7] Bartolo, P., Kruth, J. P., Silva, J., Levy, G., Malshe, A., Rajurkar, K., Mitsuishi,
M., Ciurana, J., and Leu, M., 2012, “Biomedical Production of Implants by
Additive Electro-Chemical and Physical Processes,” CIRP Ann.-Manuf. Tech-
nol.,61(2), pp. 635–655.
[8] Liua, X., Chu, P. K., and Ding, C., 2004, “Surface Modification of Titanium,
Titanium Alloys, and Related Materials for Biomedical Applications,” Mater.
Sci. Eng.: R,47(3–4), pp. 49–121.
[9] Vladescu, A., Braic, V., Balaceanu, M., Braic , M., Parau, A. C., Ivanescu, S.,
and Fanara, C., 2013, “Characterization of the Ti–10Nb–10Zr–5Ta Alloy for
Biomedical Applications—Part 1: Microstructure Mechanical Properties, and
Corrosion Resistance,” J. Mater. Eng. Perform.,22(8), pp. 2389–2397.
[10] Prakash, C., Kansal, H. K., Pabla, B. S., Puri, S., and Aggarwal, A., 2016,
“Electric Discharge Machining—A Potential Choice for Surface Modification
of Metallic Implants for Orthopedics Applications: A Review,” Proc. Inst.
Mech. Eng., Part B,230(2) pp. 231–253.
[11] Peng, P. W., Ou, K. L., Lin, H. C., Pan, Y. N., and Wang, C. H., 2010, “Effect
of Electrical-Discharging on Formation of Nanoporous Biocompatible Layer on
Titanium,” J. Alloys Compd.,492(1–2), pp. 625–630.
[12] Yang, T. S., Huang, M. S., Wang, M. S., Lin, M. H., Tsai, M. Y., and Wang,
P. Y., 2013, “Effect of Electrical Discharging on Formation of Nanoporous
Biocompatible Layer on Ti–6Al–4V Alloys,” Implant Dent.,22(4),
pp. 374–379.
[13] Lee, W. F., Yang, T. S., Wu, Y. C., and Peng, P. W., 2013, “Nanoporous Bio-
compatible Layer on Ti-6Al-4V Alloys Enhanced Osteoblast-Like Cell
Response,” J. Exp. Clin. Med.,5(3), pp. 92–96.
[14] Bin, T. C., Xin, L. D., and Zhan, W., 2011, “Electro-Spark Alloying Using
Graphite Electrode on Titanium Alloy Surface for Biomedical Applications,”
Appl. Surf. Sci.,257(15), pp. 6364–6371.
[15] Harcuba, P., Bacakova, L., Strasky, J., Bacˇ
akov
a, M., Novotn
a, K., and Jane-
cˇ ek, M., 2012, “Surface Treatment by Electric Discharge Machining of
Ti–6Al–4V Alloy for Potential Application in Orthopaedics,” J. Mech. Behav.
Biomed. Mater.,7, pp. 96–105.
[16] Strasky, J., Janecek, M., Harcuba, P., Bukovina, M., and Wagner, L., 2011,
“The Effect of Microstructure on Fatigue Performance of Ti-6Al-4V Alloy Af-
ter EDM Surface Treatment for Application in Orthopaedics,” J. Mech. Behav.
Biomed. Mater.,4(8), pp. 1955–1962.
[17] Strasky, J., Havlikova, J., Bacakova, L., Harcuba, P., Mhaede, M., and Janecek,
M., 2013, “Characterization of Electric Discharge Machining, Subsequent Etch-
ing and Shot-Peening as a Surface Treatment for Orthopedic Implants,” Appl.
Surf. Sci.,281, pp. 73–78.
[18] Havlikova, J., Strasky, J., Vandrovcova, M., Harcuba, P., Mhaede , M., Janecek,
M., and Bacakova, L., 2014, “Innovative Surface Modification of Ti–6Al–4V
Alloy With a Positive Effect on Osteoblast Proliferation and Fatigue Perform-
ance,” Mater. Sci. Eng.: C,39(1), pp. 371–379.
[19] Janecek, M., Novy, F., Strasky, J., Harcuba, P., and Wagner, L., 2011, “Fatigue
Endurance of Ti– 6Al–4V Alloy With Electro-Eroded Surface for Improved
Bone In-Growth,” J. Mech. Behav. Biomed. Mater.,4(3), pp. 417–422.
[20] Guu, Y. H., and Hosheng, H., 2001, “High Cycle Fatigue of Electrical-
Discharge Machined AISI D2 Tool Steel,” Int. J. Mater. Prod. Technol.,
16(6/7), pp. 642–657.
[21] Guu, Y. H., and Hosheng, H., 2001, “Improvement of Fatigue Life of Electrical
Discharge Machined AISI D2 Tool Steel by TiN Coating,” Mater. Sci. Eng.: A,
318(1–2), pp. 155–162.
[22] Tai, T. Y., and Lu, S. J., 2009, “Improving the Fatigue Life of Electro-
Discharge-Machined SDK11 Tool Steel Via the Suppression of Surface
Cracks,” Int. J. Fatigue,31(3), pp. 433–438.
[23] Prakash, C., Kansal, H. K., Pabla, B. S., and Puri, S., 2016, “Experimental
Investigations in Powder Mixed Electric Discharge Machining of Ti-35Nb-7Ta-
5Zr b-Titanium Alloy,” Mater. Manuf. Processes (in press).
[24] Muthuramalingam, T., and Mohan, B., 2013, “Influence of Discharge Current
Pulse on Machinability in Electrical Discharge Machining,” Mater. Manuf.
Processes,28(4), pp. 375–380.
[25] Yadav, U. S., and Yadava, V., 2015, “Experimental Modelling and Optimisation of
Process Parameters of Hole Drilling by Electrical Discharge Machining of Aero-
space Titanium Alloy,” Int. J. Manuf. Technol. Manage.,29(3–4), pp. 211–234.
[26] Mover, T. M., 2014, “Degradation of Titanium 6Al–4V Fatigue Strength Due
to Electrical Discharge Machining,” Int. J. Fatigue,64, pp. 84–96.
[27] Ntasi, A., Mueller, W. D., Eliades, G., and Zinelis, S., 2010, “The Effect of
Electro Discharge Machining (EDM) on the Corrosion Resistance of Dental
Alloys,” Dent. Mater.,26(12), pp. 237–245.
[28] Shabgard, M. R., and Alenabi, H., 2015, “Ultrasonic Assisted Electrical
Discharge Machining of Ti-6Al-4V Alloy,” Mater. Manuf. Processes,30(8),
pp. 991–1000.
041006-8 / Vol. 16, DECEMBER 2016 Transactions of the ASME
Downloaded From: http://computingengineering.asmedigitalcollection.asme.org/ on 11/07/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use
[29] Pirani, C., Iacono, F., Generali, L., Sassatelli, P., Nucci, C., Lusvarghi, L.,
Gandolfi, M. G., and Prati, C., 2016, “HyFlex EDM: Superficial Features, Met-
allurgical Analysis and Fatigue Resistance of Innovative Electro Discharge
Machined NiTi Rotary Instruments,” Int. Endod. J.,49(5) pp. 483–493.
[30] Dhakar, K., and Dvivedi, A., 2015, “Parametric Evaluation on Near-Dry
Electric Discharge Machining,” Mater. Manuf. Processes,31(4), pp. 413–421.
[31] Krishna, M. E., and Patowari, P. K., 2014, “Parametric Study of Electric Dis-
charge Coating Using Powder Metallurgical Green Compact Electrodes,”
Mater. Manuf. Processes,29(9), pp. 1131–1138.
[32] Jothimurugan, R., and Amirthagadeswaran, K. S., 2016, “Performance of Addi-
tive Mixed Kerosene–Servotherm in Electrical Discharge Machining of Monel
400
TM
,” Mater. Manuf. Processes,31(4), pp. 432–438.
[33] Kansal, H. K., Singh, S., and Kumar, P., 2005, “Application of Taguchi Metho d
for Optimization of Powder Mixed Electrical Discharge Machining,” Int. J.
Manuf. Technol. Manage.,7(2–4), pp. 329–341.
[34] Kansal, H. K., Singh, S., and Kumar, P., 2007, “Effect of Silicon Powder Mixed
EDM on Machining Rate of AISI D2 Die Steel,” J. Manuf. Processes,9(1),
pp. 13–22.
[35] Singh, A. K., Kumar, S., and Singh, V. P., 2014, “Optimization of Parameter s
Using Conductive Powder in Dielectric for EDM of Super Co 605 With
Multiple Quality Characteristics,” Mater. Manuf. Processes,29(3),
pp. 267–273.
[36] Kuriachen, B., and Mathew, J., 2015, “Effect of Powder Mixed Die lectric on
Material Removal and Surface Modification in Micro Electric Discharge
Machining of Ti-6Al-4V,” Mater. Manuf. Processes,31(4), pp. 439–446.
[37] Sidhu, S. S., Batish, A., and Kumar, S., 2014, “Study of Surface Properties in
Particulate-Reinforced Metal Matrix Composites (MMCs) Using Powder-
Mixed Electrical Discharge Machining (EDM),” Mater. Manuf. Processes,
29(1), pp. 46–52.
[38] Singh, B., Kumar, J., and Kumar, S., 2014, “Experimental Investigation on
Surface Characteristics in Powder-Mixed Electro Discharge Machining of
AA6061/10%SiC Composite,” Mater. Manuf. Processes,29(3), pp. 287–297.
[39] Singh, B., Kumar, J., and Kumar, S., 2014, “Influences of Process Parameters
on MRR Improvement in Simple and Powder-Mixed EDM of AA6061/10%SiC
Composite,” Mater. Manuf. Processes,30(1), pp. 303–312.
[40] Kansal, H. K., Singh, S., and Kumar, P., 2007, “Technology and Research
Developments in Powder Mixed Electric Discharge Machining (PMEDM),” J.
Mater. Process. Technol.,184(1–3), pp. 32–41.
[41] Kumar, H., and Davim, J. P., 2010, “Role of Powder in the Machining of Al-
10%Sicp Metal Matrix Composites by Powder Mixed Electric Discharge
Machining,” J. Compos. Mater.,45(2), pp. 133–151.
[42] Wong, Y. S., Lim, L. C., Rahuman, I., and Tee, W. M., 1998, “Near-Mirror
Finishing Phenomenon in EDM Using Powder Mixed Dielectric,” J. Mater.
Process. Technol.,79(1–3), pp. 30–40.
[43] Pecas, P., and Henriques, E., 2008, “Effect of the Powder Concentration and
Dielectric Flow in the Surface Morphology in Electrical Discharge Machining
With Powder-Mixed Dielectric (PMD-EDM),” Int. J. Adv. Manuf. Technol.,
37(11), pp. 1120–1132.
[44] Prabhu, S., and Vinayagam, B. K., 2008, “A Study on Nano-Surface Generation
in Electric Discharge Machining Process Using Multi-Wall Carbon Nanotubes,”
Int. J. Nanopart.,1(4), pp. 310–318.
[45] Kumar, H., 2014, “Development of Mirror Like Surface Characteristics Using
Nano Powder Mixed Electric Discharge Machining (NPMEDM),” Int. J. Adv.
Manuf. Technol.,76(1–4), pp. 105–113.
[46] Prakash, C., Kansal, H. K., Pabla, B. S., and Puri, S., 2014, “Processing and
Characterization of Novel Biomimetic Nanoporous Bioceramic Surface on b-Ti
Implant by Powder Mixed Electric Discharge Machining,” J. Mater. Eng.
Perform.,24(9), pp. 3622–3633.
[47] Ekmekci, N., and Ekmekci, B., 2015, “Electrical Discharge Machining of
Ti6Al4V in Hydroxyapatite Powder Mixed Dielectric Liquid,” Mater. Manuf.
Processes, (in press).
[48] Prakash, C., Kansal, H. K., Pabla, B. S., and Puri, S., 2015, “Potential of
Powder Mixed Electric Discharge Machining to Enhance the Wear and Tribo-
logical Performance of b-Ti Implant for Orthopedic Applications,” J. Nanoeng.
Nanomanuf.,5(4), pp. 261–269.
[49] Prakash, C., Kansal, H. K., Pabla, B. S., and Puri, S., 2016, “Multi-Objective Opti-
mization of Powder Mixed Electric Discharge Machining Parameters for Fabrica-
tion of Biocompatible Layer on b-Ti Alloy Using NSGA-II Coupled With
Taguchi Based Response Surface Methodology,” J. Mech. Sci. Technol. 30(9) (in
press).
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