Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings
In the present study, HFCVD nanocrystalline, microcrystalline and boron-doped nanocrystalline diamond coatings have been deposited on titanium alloy. The effect of boron doping on coefficient of friction and residual stresses of diamond coatings have been studied.
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irk-123456789-1605932019-11-13T01:25:25Z Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings Din, S.H. Shah, M.A. Sheikh, N.A. Получение, структура, свойства In the present study, HFCVD nanocrystalline, microcrystalline and boron-doped nanocrystalline diamond coatings have been deposited on titanium alloy. The effect of boron doping on coefficient of friction and residual stresses of diamond coatings have been studied. Досліджено нанокристалічні, мікрокристалічні і леговані бором нанокристалічні алмазні покриття, нанесені на титановий сплав. Вивчено вплив легування бором на коефіцієнт тертя і залишкові напруги алмазних покриттів. Исследованы нанокристаллические, микрокристаллические и легированные бором нанокристаллические алмазные покрытия, нанесенные на титановый сплав. Изучено влияние легирования бором на коэффициент трения и остаточные напряжения алмазных покрытий. 2018 Article Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings / S.H. Din, M.A. Shah, N.A. Sheikh // Сверхтвердые материалы. — 2018. — № 1. — С. 37-52. — Бібліогр.: 43 назв. — англ. 0203-3119 http://dspace.nbuv.gov.ua/handle/123456789/160593 621.793:669.295 en Сверхтвердые материалы Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України |
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Получение, структура, свойства Получение, структура, свойства |
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Получение, структура, свойства Получение, структура, свойства Din, S.H. Shah, M.A. Sheikh, N.A. Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings Сверхтвердые материалы |
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In the present study, HFCVD nanocrystalline, microcrystalline and boron-doped nanocrystalline diamond coatings have been deposited on titanium alloy. The effect of boron doping on coefficient of friction and residual stresses of diamond coatings have been studied. |
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Din, S.H. Shah, M.A. Sheikh, N.A. |
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Din, S.H. Shah, M.A. Sheikh, N.A. |
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Din, S.H. |
| title |
Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings |
| title_short |
Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings |
| title_full |
Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings |
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Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings |
| title_full_unstemmed |
Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings |
| title_sort |
tribological performance of titanium alloy ti–6al–4v via cvd-diamond coatings |
| publisher |
Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України |
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2018 |
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Получение, структура, свойства |
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| citation_txt |
Tribological performance of titanium alloy Ti–6Al–4V via CVD-diamond coatings / S.H. Din, M.A. Shah, N.A. Sheikh // Сверхтвердые материалы. — 2018. — № 1. — С. 37-52. — Бібліогр.: 43 назв. — англ. |
| series |
Сверхтвердые материалы |
| work_keys_str_mv |
AT dinsh tribologicalperformanceoftitaniumalloyti6al4vviacvddiamondcoatings AT shahma tribologicalperformanceoftitaniumalloyti6al4vviacvddiamondcoatings AT sheikhna tribologicalperformanceoftitaniumalloyti6al4vviacvddiamondcoatings |
| first_indexed |
2025-07-14T13:11:28Z |
| last_indexed |
2025-07-14T13:11:28Z |
| _version_ |
1837628065900920832 |
| fulltext |
ISSN 0203-3119. Сверхтвердые материалы, 2018, № 1 37
UDC 621.793:669.295
S. H. Din1, *, M. A. Shah2, N. A. Sheikh1
1Department of Mechanical Engineering,
National Institute of Technology, Srinagar, 190006, India
2Department of Physics, National Institute of Technology,
Srinagar, 190006, India
*sajad_08phd12@nitsri.net
Tribological performance of titanium alloy
Ti–6Al–4V via CVD-diamond coatings
In the present study, HFCVD nanocrystalline, microcrystalline and
boron-doped nanocrystalline diamond coatings have been deposited on titanium alloy.
The effect of boron doping on coefficient of friction and residual stresses of diamond
coatings have been studied. The tribological characteristics of the aforementioned
three coatings on Ti–6Al–4V substrates were studied using ball on disc micro-
tribometer, the thickness of the coatings being 3 μm. The coated Ti–6Al–4V discs were
slid against alumina (Al2O3) balls with normal load ranging from 1 to 10 N. The boron-
doped NCD coated sample disc was found to possess the lowest average coefficient of
friction ~ 0.0804 while the undoped NCD and MCD coated sample discs were found to
possess the average coefficients of friction of ~ 0.143 and ~ 0.283, respectively. Raman
spectroscopy studies revealed that the residual stresses in boron-doped nanocrystalline
coatings were tensile in nature, while the residual stresses in undoped NCD and MCD
were found to be of compressive nature.
Keywords: boron doping, CVD diamond coatings, friction coefficient.
INTRODUCTION
Titanium and its alloys are widely used in dental and load-bearing
bio-implants, owing to their advantageous properties such as low density, low
modulus, high strength-to-weight ratio, exceptional fatigue strength, and outstanding
formability, as well as superior biocompatibility and corrosion resistance [1–3]. A
deposition on a surface is achieved by the chemical vapor deposition method which
involves a gas phase. A chemical reaction occurs above the solid surface. For
producing diamond films, all chemical vapor deposition techniques require a means
of actuating gas-phase carbon comprising precursor molecules [4, 5]. Diamond thin
films have been deposited using a variety of chemical vapor deposition techniques,
which include hot filament, microwave chemical vapor deposition, RF plasma, and
DC jet [6–9]. Substrate conditions, which include the surface preparation procedure,
play an important role in the diamond nucleation on a given substrate. In order to
enhance the density of diamond nuclei, scratching the substrate with diamond grit is
quite effective. The scratching results in diamond residual particles which provide
seeds for diamond growth [10]. The hot filament chemical vapor deposition
technique possesses many advantages over other methods, being much simpler and
easier to adopt for a large-area deposition at a lower cost, which is of special interest
for many applications [11].
Due to the high specific strength, biocompatibility, and corrosion resistance, the
titanium finds wide application in aerospace, biomedicine and chemical
© S. H. DIN, M. A. SHAH, N. A. SHEIKH, 2018
www.ism.kiev.ua/stm 38
engineering [12–14]. By the chemical vapor deposition diamond films wear loss
can be reduced, since highly adherent diamond coatings can be deposited on
titanium [15–16]. The effect of doping on the mechanical properties of diamond
films have not been investigated thoroughly [17–20]. Hence in order to broaden the
applications of doped diamond films, tribological properties need to be
investigated. Boron atoms can be easily incorporated into the diamond lattice,
which forms a p-type semiconductor with tunable electrical conductivity. Boron-
doped diamond has been extensively researched in electrical and semiconductor
materials [21–23]. A real application of boron-doped diamond on titanium is its
usage as an electrode material. By doping the chemical vapor deposited diamond
film with some impurities as boron, nitrogen, or sulphur, the wide gap of diamond
(5.5 eV) can be reduced, producing a semiconductor material. Principally, boron-
doped diamond has achieved good results for semiconductor sensor applications,
both in the solid-state electronics along with electrochemistry. The diameter film
properties with high mobility of carriers, higher thermal conductivity, electrical
consistency and compatibility with aggressive media, can be widely explored in
sensors for toxic gases and also for electrodes for hostile chemical environments
[24–29]. It can be found that the tribological properties of boron-doped diamond
films on titanium are not clear.
In the present communication, the tribological properties of nanocrystalline
diamond films, microcrystalline diamond films and boron-doped diamond films
deposited on titanium alloy (Ti–6Al–4V) are investigated. Smooth and adhesive
coatings were deposited on titanium alloy substrates, with a thickness of 3 µm. The
substrates were chemically etched and deposition was done with hot filament
chemical vapor deposition technique. Three types of samples were prepared
separately, namely, nanocrystalline diamond coatings, microcrystalline diamond
coatings and boron-doped nanocrystalline diamond coatings. Raman spectroscopy
technique was used to identify the nature and estimation of residual stresses, and to
identify the boron content of a diamond film. The tribological properties are
compared. We focus on the tribological behavior of diamond films on titanium
alloy in ambient air. Systematic investigation of the relationship between applied
normal load and frictional coefficient was carried out to better understand the
tribological behavior of the nanocrystalline, microcrystalline, and boron-doped
nanocrystalline diamond coatings.
EXPERIMENTAL DETAILS
The nanocrystalline, microcrystalline and boron-doped diamond films are
deposited using hot filament chemical vapor deposition apparatus, in separate
experiments. The precursor of boron is trimethyl borate (C3H9BO3). Titanium alloy
samples of diameter 25 and 3 mm thickness in dimensions were slided using
silicon carbide (SiC) and cleaned with deionized water. The samples were etched
in the solution of HF: H2SO4: DI water, rinsed in deionized water three times for 3
min each and blown dry with air gun. The mirror finish was obtained by polishing
the samples with diamond paste (2.0, 1.0 and 0.5 μm). An ultrasonicator was used
to clean the samples with acetone for 30 min and then dried thoroughly by a hot
drier. Dimethyl sulphoxide (DMSO) solution containing diamond seedings of size
4 μm were used. Before deposition of nanodiamond films, the titanium samples
were dispersed in it. This is done using a low power ultrasonicator for 15 min. The
samples were again cleaned with ethanol in an ultrasonicator for 1 min and placed
inside the cold walled aluminum chamber of hot filament chemical vapor
deposition system (sp3 Diamond Technologies Inc., USA). An array of 31 parallel
ISSN 0203-3119. Сверхтвердые материалы, 2018, № 1 39
wires of (0.12 mm) diameter filaments, with 12 mm wire to wire spacing and stand
off distance of 18 mm, was placed above the samples. For acquiring NCD coatings
a rotary pump was used to continuously pump the hot filament chemical vapor
deposition (HFCVD) chamber. During the preparation of NCD samples the
methane (90 sccm) diluted in excess of hydrogen (2250 sccm), were quantified at
carefully controlled rates. The assembly of gas distribution allowed the control of
the gas flow patterns in and around the filament assembly and the sample to ensure
uniformness in the coatings. For deposition of NCD coatings, the set chamber
pressure during the deposition was 7 Torr, which was maintained accurately by a
throttle valve connected to the rotary pump. A two color pyrometer monitored the
temperature of tungsten filament. It was found to be 2200 °C. A k-type
thermocouple was used to measure the temperature of titanium alloy samples. The
thermocouple was located beneath the titanium alloy samples. It was found to be
800 °C. The whole growth process was performed for 3 h and the thickness of the
film was estimated to be 3 μm.
In a separate experiment, for the purpose of acquiring microcrystalline diamond
coatings, the methane (45 sccm), diluted in excess of hydrogen (2250 sccm), were
quantified in at carefully controlled rates. The set chamber pressure during the
deposition was 36 Torr, which was maintained constant throughout the experiment.
The third experiment comprised of the same experimental conditions as that of the
first one except that a small content of boron (0.5 %) was added to the samples.
Structural characteristics of these coatings were studied using grazing incidence
X-ray diffraction (PANalytical) technique with CuKα (λ = 0.154 nm) radiation
at 3° grazing angle and confocal Raman microscope (Alpha 300R, WITec) at an
excitation wavelength of 448 nm. Surface morphology of these coatings were
analyzed using a high resolution scanning electron microscope (HRSEM, Quanta
3D, FEI). Friction characteristics were carried out using a ball-on-disc type linear
reciprocating micro-tribometer (CSM Instruments, Switzerland) under dry sliding
conditions. Alumina (Al2O3) ball of size 6 mm was used as sliding ball, applying
at three different normal loads of 1, 5 and 10 N. A sliding speed of 8 cm/s,
frequency of 2 Hz and a friction stroke length of 5 mm were used for the overall
time period of 20 min. The growth parameters are shown in Table 1.
Table 1. Growth parameters for the deposition of NCD and BDNCD
coatings
Temperature, °C
Coating
Process
pressure,
Torr
CH4/H2,
ratio, % filament substrate
Boron
concentration,
%
Duration,
hrs
NCD 12 90/2250, 4 2200 800–850 – 3
MCD 36 45/2250, 2 2200 800–850 – 3
BDNCD 12 90/2250, 4 2200 800–850 0.5 3
RESULTS AND DISCUSSIONS
Characterization of doped diamond films by scanning electron microscopy
The surface roughness and microstructure were examined using a field emission
SEM (Quanta 3D, FEI). The NCD coating demonstrates a fairly smooth surface
that replicates the texture of the substrate surface. A cauliflower type of
morphology is generally shown by the (NCD) of CVD diamond coatings. Figure 1,
a shows the general surface morphology of the (NCD) of the CVD-diamond
www.ism.kiev.ua/stm 40
coatings. The MCD coating exhibits clear multi-facet diamond crystals. The MCD
coatings have rougher surface because of diamond crystals. MCD coatings exhibit
columnar structure of grains and faceted form of the surface morphology. The
MCD coatings are shown in Fig 1, b. Figure 1, c shows the boron-doped NCD
coatings which are similar in morphology as undoped NCD coatings.
a
b
c
Fig. 1. Surface morphology of NCD (a), MCD (b) and boron-doped (c) CVD diamond coatings.
XRD analysis
The phase analysis of the deposited films was carried out by X-ray diffraction
(X’pert Pro, PANalytical) with CuKα radiation. The XRD patterns of
nanocrystalline, microcrystalline and boron-doped nanocrystalline diamond
coatings are shown in Figs. 2, a, 2, b, and 2, c, respectively. Sharp and strong peaks
of cubic diamond coatings were observed at the (111) crystal and (220) crystal
planes at diffraction angles of 44° and 75.5°, respectively, for these coatings, along
with the substrate (Ti–6Al–4V) peaks. This confirms the crystallinity of the
coatings. Also the variations in these peaks show that its grain size is more than
diamond coatings. Since, with the addition of boron content the grain size and
lattice parameter of diamond film may be changed.
The average evident sizes of diamond grains along the [111] and [220]
directions were obtained by fitting the (111) and (220) diffraction peaks,
respectively, and putting on the Scherrer formula [30]:
θ
λ=
cossizeW
k
D ,
ISSN 0203-3119. Сверхтвердые материалы, 2018, № 1 41
where, K is a constant which depends on the specific (hkl) reflection as well as on
the grain shape and Wsize indicates the full width at half maximum (FWHM)
because of the influence of size and is given by the following formula:
2
IRF
2
size WWW −= ,
W is the FWHM of the calculated diffraction peak and WIRF, the FWHM of the
instrumental broadening. In the calculation, K = 1 was assumed. The relative
variations of size values are practically significant in this case, and independent
calculations were carried out on the (111) and (220) reflections.
30 40 50 60 70 80
In
te
ns
it
y,
a
rb
. u
n
it
s
2θ, deg
D on Ti6Al4V
D (111)
D (220)
a
30 40 50 60 70 80
MCD on Ti6Al4V
D
(111)
D (220)
In
te
n
si
ty
,
ar
b.
u
n
it
s
2θ, deg
b
20 30 40 50 60 70 80
Boron Doped
Diamond on Ti6Al4V
D (220)D (111)
In
te
n
si
ty
,
ar
b.
u
n
it
s
2θ, deg
c
Fig. 2. X-ray diffraction patterns of CVD-diamond coatings: NCD (a), MCD (b) and boron-doped
(c) coatings.
Raman spectroscopy and residual stress analysis
Raman spectra of the deposited films were documented using a confocal
microscope (Alpha 300, Witec) with an excitation radiation of 448 nm of a Nd:YAG
laser activated at less than 20 mW. Raman spectroscopy was used to identify the
chemical structure as well as crystalline quality of the diamond coatings. In this
respect, stress-free crystalline diamond coating reveals Raman peak at 1332 cm−1
corresponding to the first-order phonon mode of T2g symmetry [31]. Raman
spectrum of MCD coating confirms the micro-crystallinity. MCD exhibits columnar
structure of grains and faceted form of surface morphology. First order Raman peak
shift towards higher side centered at 1333 cm−1 is indicative of the presence of
residual compressive stress in both NCD and MCD coatings. Mainly, this
compressive residual stress is due to the difference in thermal expansion coefficients
between the substrate and coating [32–35]. Figures 3, a, 3, b and 3, c show the
www.ism.kiev.ua/stm 42
Raman spectrum of NCD, MCD and boron-doped CVD coatings. Residual stresses
can be calculated from –0.348(vm ‒ v0) GPa for fundamental Raman peak at vm,
where v0 =1332 cm–1 and vm = 1333 cm–1. Thus, both NCD and MCD diamond
coating systems contain a compressive stress of –0.348 GPa (the negative sign
indicates a compressive stress). In the case of NCD coatings, two other peaks ν1 and
ν3 are characteristics of in-plane (C–H) and stretching (C–C) vibrational modes,
respectively. The existence of these modes was ascribed to the formation of trans-
polyacetylene (TPA) chain in the grain boundaries, which is a familiar characteristic
of NCD coatings. A cauliflower type of growth is generally seen with the NCD
coatings [36–39]. As for boron-doped diamond films, 1332 cm–1 peak changes
towards an asymmetric Fano effect. The broad bands at around 500 and 1250 cm–1
may well be related to the actual boron incorporation in the lattice. Their position
accepts with two maxima of the phonon density of states (PDOS) of diamond. The
shifts of Raman diamond peak to the higher and lower frequency are corresponded to
compressive and tensile stresses in the diamond films, respecttively. Undoped
diamond films show compressive stress, whereas tensile in-plane bi-axial stress can
be realized in B–doped diamond films. The tensile stress is mostly induced by high
defect density in the B–doped diamond films and node-blocked sliding effect at the
grain boundary. Residual stresses can be calculated from –0.348(vm ‒ v0) GPa for
fundamental Raman peak at vm, where v0 = 1332 cm–1 and vm = 1301 cm–1, σ =
–0.348(1301 ‒ 1332) GPa. Thus, boron-doped diamond coating system contains a
tensile stress of 10.788 GPa, where positive sign indicates tensile stress.
1000 1250 1500 1750 2000
Raman shift, cm
–1
1169
1333
1531
1440
In
te
ns
it
y,
a
rb
. u
n
it
s
a
0 500 1000 1500 2000
1333 (Diamond)
Raman shift, cm
–1
In
te
n
si
ty
,
ar
b.
u
n
it
s
b
0 500 1000 1500 2000
B�Doped Diamond470
986
1208
1301
1536
Raman shift, cm
–1
In
te
ns
it
y,
a
rb
. u
ni
ts
c
Fig. 3. Raman spectra of CVD-diamond coatings: NCD (a), MCD (b), boron-doped (c) coatings.
ISSN 0203-3119. Сверхтвердые материалы, 2018, № 1 43
Friction characteristics of the NCD, MCD and boron-doped NCD
coatings against alumina balls
The friction coefficient curves of NCD, MCD and boron-doped diamond films
sliding with Al2O3 balls are shown in Figs. 4, 5 and 6, respectively, for a sliding
speed of 8 m/s and a load of 1, 5 and 10 N, respectively. Figs. 4, a, 5, a and 6, a
show the friction coefficient of NCD, MCD and BDNCD at 1 N, respectively.
Figures 4, b, 5, b and 6, b show the friction coefficient of NCD, MCD and BDNCD
at 5 N. Figures 4, c, 5, c and 6, c show the friction coefficient of NCD, MCD and
BDNCD at 10 N, respectively. Figures 4, d, 5, d and 6, d show the average friction
coefficient of NCD, MCD and BDNCD, respectively. Table 2 shows the summary
of residual stresses and variation in coefficient of friction. Figure 7 shows the
comparison of average coefficient of friction between NCD, MCD and BDNCD
coatings. Figure 8, a, shows the Raman spectrum of wear track of NCD coatings at
10 N while Figs. 8, b and 8, c show the Raman spectrum of wear track of MCD and
BDNCD CVD diamond coatings at 10 N respectively. Figures 9, a and 9, b shows
the surface morphology of the wear tracks of NCD and MCD coatings at 10 N
while Fig. 9, c shows the surface morphology of the wear track of boron-doped
CVD diamond coatings at 10 N. Figures 10, 11 and 12 show the EDX analysis of
NCD, MCD and boron-doped coatings while there compositions are given in
Tables 3, 4 and 5 respectively. The loud wavering of the friction coefficient
observed at 1N are due to the surface roughness. After a longer test carried out in
these conditions, the diamond coating on the disc is found to be intact as shown by
0 5 10 15 20
0.1
0.2
0.3
0.4
C
oe
ff
ic
ie
n
t
of
f
ri
ct
io
n
Rubbing time, min
a
0 5 10 15 20
0.05
0.10
0.15
0.20
0.25
0.30
C
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
Rubbing time, min
b
0 5 10 15 20
0.05
0.10
0.15
0.20
0.25
C
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
Rubbing time, min
c
0 2 4 6 8 10
0.11
0.12
0.13
0.14
0.15
0.16
0.17
A
ve
ra
ge
c
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
Load, N
d
Fig. 4. Tribological characteristics of alumina ball sliding against NCD coating at 1 (a), 5 (b), 10
(c) N and average coefficient of friction (d).
www.ism.kiev.ua/stm 44
0 5 10 15 20
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
C
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
Rubbing time, min
a
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0.05
0.10
0.15
0.20
0.25
0.30
0.35
C
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
Rubbing time, min
b
0 5 10 15 20
0.05
0.10
0.15
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0.25
0.30
0.35
C
oe
ff
ic
ie
n
t o
f f
ri
ct
io
n
Rubbing time, min
c
0 2 4 6 8 10
0.265
0.270
0.275
0.280
0.285
0.290
0.295
0.300
0.305
0.310
A
ve
ra
ge
c
oe
ff
ic
ie
n
t o
f f
ri
ct
io
n
Load, N
d
Fig. 5. Tribological characteristics of alumina ball sliding against MCD coating at 1 (a), 5 (b), 10
(c) N and average coefficient of friction (d).
the SEM and indicated by the surface roughness values, which remain unchanged.
At higher loads, the friction coefficient measured in the same track stabilizes after
about 12 min. At the beginning of the applied load we can observe a peak which
corresponds to the adaptation of the contact of both counter-faces. At the end of the
test carried out at 10 N on the coating a wear track of 230 µm in width was formed
on the diamond coated disc. The high magnification image of this area shows that
the worn surface is significantly polished. When increasing the time, at a sliding
speed of 8 m/s and a load of 10 N, the friction coefficient gradually decreases after
a time period of 3 min. After the initial high peak, the curve of boron-doped
diamond films first drops to a low value and then increases to some degree before
transiting to the steady state. While for undoped diamond films, the coefficient
directly transits to the steady state. The boron-doped diamond films demonstrate
exceptional tribological property. They show the lowest wear rate of the films and
the counterpart ball, followed by undoped diamond films. The adhered transferred
materials make the transition regime in the friction coefficient evolution of boron-
doped diamond films differ from that of undoped diamond films. Among all the
tested diamond films, friction tests suggest that the boron-doped diamond films
exhibit the lowest friction coefficient and wear rate, because of its diamond grain
refinement effect. A lower friction coefficient is found in boron-doped diamond films
than that of undoped ones. No variation of the total volume wear rate as a function of
time was evidenced during the test since the vertical movement was negligible, a few
micrometers at the end of the test. At this point, the final wear rate of the ball is about
ISSN 0203-3119. Сверхтвердые материалы, 2018, № 1 45
0 5 10 15 20
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
C
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
Rubbing time, min
a
0 5 10 15 20
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
C
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
Rubbing time, min
b
0 5 10 15 20
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
C
oe
ff
ic
ie
n
t o
f f
ri
ct
io
n
Rubbing time, min
c
0 2 4 6 8 10
0.078
0.079
0.080
0.081
0.082
0.083
A
ve
ra
ge
c
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
Load, N
d
Fig. 6. COF of boron-doped diamond coatings on titanium alloy at 1 (a), 5 (b), 10 (c) N and
average COF (d).
5×10–17 m3(N/m). The wear of the diamond coated disc is too low to be measured
and the wear track is just polished, as detected by SEM and confirmed by the AFM
measurements. This lack of the coating wear of the disc results from the short test
duration due to the ball wearing more quickly. Alumina is a chemically inert
ceramic compound and sliding interaction of diamond coatings against alumina
material is purely mechanical. Low and stable friction coefficient values of around
0.0804 were observed with the boron-doped NCD coating. The stable and low
friction coefficient of the boron-doped NCD coating was attributed to the chemical
inertness of the mating materials and also due to the continuous availability of the
lubricious non-diamond graphitic phases at the grain boundaries of NCD coating.
On the other hand, slightly high and unstable friction behavior was observed during
the sliding of MCD coating against alumina ball. High run-in friction values of
~ 0.283 (average) were observed with the MCD coatings. The high run-in friction
behavior of the MCD coating as compared to the NCD and BDNCD coatings was
attributed to its sharp and rough surface asperities. When increasing the time, at a
sliding speed of 8 m/s and a load of 10 N, the friction coefficient first increases and
then decreases gradually after a time period of 5 min and remains constant after
12 min. The NCD, MCD and doped diamond films undergo similar friction
coefficient advancement. Following the initial peak, the coefficient of friction
transit to a lower value and at last reaches a steady state. In case of the boron-
doped diamond films, the coefficient of friction also starts with a high value but
falls to a low value quickly. An increasing regime then can be observed and finally
the curve attains a fairly steady state. The averaged friction coefficient is incurred
www.ism.kiev.ua/stm 46
by undertaking statistics on the data composed after sliding for 20 min. The stable
friction coefficient of boron-doped diamond films is lower than that of NCD and
MCD diamond films, even though the boron-doped diamond films present larger
crystallites and rougher surface. The lower friction coefficient of boron-doped
diamond films is due to the interaction mechanism between two contacting
surfaces being altered because of a boron incorporation. The boron carbide
chemical bonds may exist in the boron-doped diamond films; it would assist in
changing the surface frictional energy dissipation and thus change the coefficient
of friction [40–43]. The oxide generated by the friction may serve as a solid
lubrication, which will help to decrease COF for boron-doped diamond films. The
lowest coefficient of friction of 0.0804 is given by boron-doped diamond films.
The friction coefficient of B-doped diamond films is lower than that of the
undoped diamond films though the B-doped diamond films present bigger
crystallites and rougher surface.
Table 2. Tribological results
Coating type σ (residual stress) Variation in coefficient of friction
NCD –0.348 GPa ~ 0.17–0.11
MCD –0.348 GPa ~ 0.305–0.272
BNCD 10.788 GPa ~ 0.0825–0.0786
NCD MCD BDNCD
0
0.05
0.10
0.15
0.20
0.25
0.30
C
oe
ff
ic
ie
nt
o
f f
ri
ct
io
n
0.143
0.283
0.0804
Fig. 7. Comparison of average coefficients of friction of NCD, MCD and boron-doped diamond
coatings.
0 500 1000 1500 2000
534
1334
1496
Raman shift, cm
–1
In
te
n
si
ty
, a
rb
. u
n
it
s
a
0 500 1000 1500 2000
1337
537
1481
Raman shift, cm
–1
In
te
n
si
ty
,
ar
b.
u
n
it
s
b
Fig. 8. Raman spectra of wear track of CVD-diamond coatings NCD (a), MCD (b) and of boron-
doped CVD-diamond coatings (c).
ISSN 0203-3119. Сверхтвердые материалы, 2018, № 1 47
0 500 1000 1500 2000
445
1195
1525
Raman shift, cm
–1
In
te
ns
it
y,
a
rb
. u
ni
ts
c
Fig. 8. (Contd.)
a
b
c
Fig. 9. SEM images of wear tracks of CVD-diamond coatings: surface morphology of NCD (a),
MCD (b) and boron-doped CVD (c) diamond coatings.
0 1 2 3 4 5 6 7 8 9 keV
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
001
C
ou
nt
s,
×
1.
E
+
3
Fig. 10. EDX analysis of wear track of NCD coatings.
www.ism.kiev.ua/stm 48
0 1 2 3 4 5 6 7 8 9 keV
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
001
C
ou
n
ts
,
×1
.E
+
3
Fig. 11. EDX analysis of wear track of MCD coatings.
0 1 2 3 4 5 6 7 8 9 keV
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
001
C
ou
n
ts
, ×
1.
E
+
3
Fig. 12. EDX analysis of wear tracks of boron-doped coatings.
Table 3. Energy dispersive X-ray analysis (EDXA) of NCD coatings
Chemical
formula
mass % at % Sigma Net K ratio Line
C 81.44 88.51 0.08 50488 0.0206980 K
O 11.48 9.37 0.21 2205 0.0030696 K
Al 0.92 0.45 0.04 2880 0.0012868 K
Ti 6.04 1.65 0.08 10117 0.0104212 K
V 0.12 0.03 0.05 177 0.0002055 K
Total 100.00 100.0
Chemical
formula
mass % mol % Cation Sigma Net K ratio Line
C 86.63 97.82 0.08 50488 50488 0.0206980 K
Al2O3 1.90 0.25 0.08 0.08 2880 0.0012868 K
TiO2 11.23 1.91 0.15 0.15 10117 0.0104212 K
V2O5 0.24 0.02 0.09 0.09 177 0.0002055 K
Total 100.00 100.0
ISSN 0203-3119. Сверхтвердые материалы, 2018, № 1 49
Table 4. Energy dispersive X-ray analysis (EDXA) of MCD coatings
Chemical
formula
wt % at % Sigma Net K ratio Line
C 92.17 96.13 0.27 5346 0.0019595 K
O 3.12 2.45 0.33 57 0.0000688 K
Al 0.97 0.45 0.13 168 0.0001081 K
Ti 3.72 0.97 0.35 221 0.0004347 K
V 0.02 0.00 0.27 1 0.0000020 K
Total 100.00 100.0
Chemical
formula
wt % mol % Cation Sigma Net K ratio Line
C 91.96 98.77 0.00 0.27 5346 0.0019595 K
Al2O3 1.83 0.23 4.12 0.24 168 0.0001081 K
TiO2 6.18 1.00 8.86 0.59 221 0.0004347 K
V2O5 0.03 0.00 0.04 0.48 1 0.0000020 K
Total 100.00 100.0
Table 5. Energy dispersive X-ray analysis (EDXA) of boron-doped
coatings
Chemical
formula
wt % at % Sigma Net K ratio Line
C 94.51 97.86 0.09 52611 0.0192846 K
O 1.33 1.03 0.11 212 0.0002548 K
Al 0.15 0.07 0.03 230 0.0001478 K
Ti 3.79 0.98 0.11 2025 0.0039870 K
V 0.22 0.05 0.08 99 0.0002267 K
Total 100.00 100.0
Chemical
formula
wt % mol % Cation Sigma Net K ratio Line
C 93.18 98.96 0.00 0.09 52611 0.0192846 K
Al2O3 0.27 0.03 0.74 0.06 230 0.0001478 K
TiO2 6.16 0.98 10.71 0.18 2025 0.0039870 K
V2O5 0.38 0.03 0.59 0.14 99 0.0002267 K
Total 100.00 100.00 12.04
CONCLUSIONS
The effect of boron doping on residual stresses and frictional coefficient of
CVD diamond coatings has been analyzed. Boron concentration changes the
compressive residual stresses to tensile. Further, at a boron content of 0.5 %, there
is nearly 43.77 % reduction in friction coefficient. The results of Raman spectra
indicate that the boron-doped diamond films present tensile stress while undoped
diamond films show compressive stresses. The friction tests reveal that the boron-
www.ism.kiev.ua/stm 50
doped diamond films presented lower friction coefficient, when sliding with Al2O3
ceramic materials, compared to undoped diamond films although boron-doped
diamond films have comparatively larger grain size and rougher surface. The
average friction coefficient of BDNCD was 0.0804 at different loads when sliding
against Al2O3 balls, whereas NCD and MCD coatings exhibited a higher value of
0.143 and 0.283, respectively.
ACKNOWLEDGMENT
The authors thank Prof. M. S. Ramachandra Rao, MSRC lab, IIT Madras, for
the deposition of coatings and C. Anandan (Surface Engineering Division, NAL,
Bangalore, India) for doing tribological tests and Prof. Kamal K. Kar, IIT Kanpur.
Досліджено нанокристалічні, мікрокристалічні і леговані бором
нанокристалічні алмазні покриття, нанесені на титановий сплав. Вивчено вплив
легування бором на коефіцієнт тертя і залишкові напруги алмазних покриттів. Трибо-
логічні характеристики вищезазначених трьох видів покриттів на підкладках Ti–6Al–4V
вивчали з використанням мікротрибометра “куля на диску”, товщина покриттів стано-
вила 3 мкм. Диски з покриттям Ti–6Al–4V ковзали відносно куль з оксиду алюмінію (Al2O3)
з нормальним навантаженням від 1 до 10 Н. Легований бором зразок диска з NCD-
покриттям мав найнижчий середній коефіцієнт тертя ~ 0,0804, тоді як нелеговані диски
з покритями NCD і MCD мали середні коефіцієнти тертя ~ 0,143 і ~ 0,253 відповідно.
Дослідження за допомогою рамановскої спектроскопії виявили, що залишкові напруги були
за природою такими, що розтягують, тоді як залишкові напруги в нелегованих NCD і
MCD виявилися такими, що стискають.
Ключові слова: легування бором, CVD алмазні покриття, коефіцієнт
тертя.
Исследованы нанокристаллические, микрокристаллические и легирован-
ные бором нанокристаллические алмазные покрытия, нанесенные на титановый сплав.
Изучено влияние легирования бором на коэффициент трения и остаточные напряжения
алмазных покрытий. Трибологические характеристики вышеупомянутых трех видов
покрытий на подложках Ti–6Al–4V изучали с использованием микротрибометра “шар на
диске”, толщина покрытий составляла 3 мкм. Диски с покрытием Ti–6Al–4V скользили
относительно шаров из оксида алюмия (Al2O3) с нормальной нагрузкой от 1 до 10 Н.
Легированный бором образец диска с NCD-покрытием имел самый низкий средний
коэффициент трения ~ 0,0804, тогда как нелегированные диски с покрытиями NCD и
MCD имели средние коэффициенты трения ~ 0,143 и ~ 0,253 соответственно. Исследова-
ния с помощью рамановской спектроскопии выявили, что остаточные напряжения были
по природе растягивающими, тогда как остаточные напряжения в нелегированных NCD
и MCD оказались сжимающими.
Ключевые слова: легирование бором, CVD алмазные покрытия,
коэффициент трения.
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Received 14.06.16
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