M. BASIAGA et al.: COMPARISON OF THE PHYSICOCHEMICAL PROPERTIES OF Al2O3 LAYERS ...
637–641
COMPARISON OF THE PHYSICOCHEMICAL PROPERTIES OF
Al2O3 LAYERS APPLIED TO THE SURFACES OF cpTi AND THE
Ti6Al7Nb ALLOY USING THE ALD METHOD
PRIMERJAVA FIZIKALNO-KEMIJSKIH LASTNOSTI Al2O3 PLASTI,
NANE[ENIH NA cpTi POVR[INE IN ZLITINO Ti6Al7Nb Z
UPORABO ALD METODE
Marcin Basiaga1, Marcin Staszuk2, Tomasz Tañski2, Agnieszka Hyla1,
Witold Walke1, Cezary Krawczyk3
1Silesian University of Technology, Faculty of Biomedical Engineering, ul. Roosevelta 40, 41-800 Zabrze, Poland
2Silesian University of Technology, Faculty of Mechanical Engineering, ul. Konarskiego 18A, 44-100 Gliwice, Poland
3Zabrze Medical College, Department of Dental Technology, ul. 3 Maja 63, 41-800 Zabrze, Poland
marcin.staszuk@polsl.pl
Prejem rokopisa – received: 2016-07-22; sprejem za objavo – accepted for publication: 2016-11-08
doi:10.17222/mit.2016.220
Literature data show that atomic-layer deposition (ALD) is a very important method for depositing layers due to the mechanical
and physicochemical properties of the surface. In the literature, little space is devoted to layers of Al2O3, which could also have
a major impact on improving the physicochemical properties of metallic biomaterials. Therefore, the aim of this research was to
determine the influence of the Al2O3 layer formed by the ALD method on the physicochemical properties of metallic
biomaterials. Based on the results, a beneficial effect on the pitting and crevice-corrosion resistance of the applied Al2O3 layer
was determined, compared to the initial state, devoid of the layer, regardless of the substrate used. On the other hand, the
performed surface-wettability tests showed no influence of the ALD temperature on the obtained angle values. Proposing
appropriate conditions for the surface treatment using the ALD method has some promise and will contribute to the
development of a technological process with defined parameters for oxide-layer manufacture for implants used in bone surgery.
Keywords: cpTi (Grade 4), Ti6Al7Nb alloy, Al2O3 layer, adhesion, corrosion resistance
Podatki iz literature ka`ejo, da je depozicija atomskih plasti (ALD) zelo pomembna metoda za nana{anje plasti zaradi
mehanskih in fizikalno-kemijskih lastnosti povr{ine. V literaturi so plasti Al2O3 sicer le malo omenjene pa vendar imajo lahko
velik vpliv na izbolj{anje fizikalno-kemijskih lastnosti kovinskih biomaterialov. Cilj raziskave je bil zato ugotoviti vpliv Al2O3
sloja, tvorjenega z metodo ALD, na fizikalno-kemijske lastnosti kovinskih biomaterialov. Na osnovi rezultatov smo dolo~ili
ugoden u~inek uporabljene Al2O3 plasti pri odpornosti na luknji~asto in {pranjsko korozijo, v primerjavi z za~etnim stanjem, ki
je bila brez sloja, ne glede na uporabljeno podlago. Po drugi strani pa so izvedeni testi povr{inske vpojnosti pokazali, da
temperatura ALD-metode ne vpliva na dobljene kotne vrednosti. Ustrezni pogoji, predlagani za povr{insko obdelavo z uporabo
ALD-metode, veliko obetajo in bodo prispevali k razvoju tehnolo{kega procesa z dolo~enimi parametri za izdelavo vsadkov, ki
se uporabljajo v kirur{ki medicini in pri operacijah kosti.
Klju~ne besede: cpTi (Grade 4), Ti6Al7Nb zlitina, Al2O3 plast, oprijem, odpornost proti koroziji
1 INTRODUCTION
Material implanted into human tissues and body
fluids must have a bio-electronic compatibility, and so
have the appropriate electric and magnetic properties,
similar to those of the surrounding living matter, which
has mostly a dielectric characteristic. In addition, the
selected set of mechanical properties of such a material
should provide good relations in the implant-tissues-
body-fluids system that are essential to the realization of
biophysical cooperation and flexible load transfer. The
materials’ physicochemical properties chosen this way
will protect the implant against the damaging process of
its destruction, and consequently, general and reactive
responses will be minimized and so will be the process
of metalosis.1–4
To prevent such negative phenomena surface treat-
ment methods, e.g., coating, are used on implants.
However, until now satisfactory results have not been
achieved in that manner. Therefore, a continuous search
for the best solutions relating to the methodology, the
chemical composition and physicochemical properties of
the layers produced is being conducted by many experts
in the field.5–8 An attempt to improve the physical and
chemical properties of implants used in bone surgery
was taken by J. Szewczenko,9 who carried out the pro-
cess of anodic oxidation on titanium alloys. Similar
studies were conducted by W. Walke,10,11 who deposed
layers of TiO2 and SiO2 on 316 LVM steel using the
sol-gel method.
Among the many techniques for applying layers,
ALD (Atomic Layer Deposition) deserves special atten-
tion because it does not change the geometrical features
of the implant and allows manufacturers to control the
layer thickness. The method was created in Finland in
the 1970s. The method is based on the CVD technique
Materiali in tehnologije / Materials and technology 51 (2017) 4, 637–641 637
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 67.017:62-4-023.7:620.193 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(4)637(2017)
(Chemical Vapour Deposition). Otherwise, it can be
described as layer-by-layer coating deposition. It is
characterized by: chemisorption, which is the formation
of strong chemical bonds between the precursors, im-
pregnation, which is important in achieving uniformity
of the layer, sequencing, which is a key feature of this
method consisting of the fact that the precursors are
introduced into the chambers in turns.
Literature data show that ALD is a very important
method of depositing layers due to the mechanical and
physicochemical properties of the surface. For this
reason, numerous studies are conducted on it. A. Purni-
awan et al.7 performed a study that uses a low surface
roughness and the uniformity of the TiO2 deposited by
ALD in the creation of biomedical sensors used in the
diagnosis of leaks during the operation of anastomosis of
the colon, pancreas, etc. In this experiment, a layer of
TiO2 was used as an evanescent waveguide. After a
series of tests, it was found that the layer is suitable for
use as a biomedical sensor, detecting dangerous effects
in humans.3 Another example might be the use of a SiO2
layer applied by ALD in order to improve the corrosion
resistance of stainless steel. Layers were applied with
different thicknesses: 300 nm, 100 nm, 30 nm, 10 nm. A
measurement of the material’s hardness using the
Vickers method and a test of the layer’s adhesion to the
substrate were conducted. As a result the corrosion resis-
tance was determined. Studies have shown that the
thicker the layer the greater the delamination after the
hardness test, and so the adhesion to the substrate is
poorer. The layers deposited by ALD also increased the
corrosion resistance of steel by reducing the corrosion
current, and increasing the passive areas.12
In the literature, little space is devoted to layers of
Al2O3, which could also have a major impact on im-
proving the physicochemical properties of metallic bio-
materials. Therefore, the aim of the completed research
was to determine the influence of an Al2O3 layer formed
by the ALD method on the physicochemical properties
of metallic biomaterials.
2 EXPERIMENTAL PART
The study was conducted on the Al2O3 layer applied
by ALD on the two selected metal substrates, i.e., cpTi
and Ti6Al7Nb (Table 1). Samples were provided in the
form of discs with a diameter of 14 mm and a thickness
of 3 mm. The samples were subjected to a preliminary
surface modification consisting of vibration machining
using suitable ceramic grinding particles required to
obtain a constant roughness Ra < 0.4 μm. Then, the sur-
face of the samples was subjected to electrochemical
polishing in a solution based on chromic acid (E-395
made by POLIGRAT Gmbh Company), with a current
density = 10÷30 A/cm2. The treatment made it possible
to obtain a surface roughness of Ra = 0.1 μm. The surface
was then covered with an Al2O3 layer using ALD
(PICOSUN). The process of applying the layer was
carried out under recurrent conditions for both materials.
To deposit an Al2O3 layer using ALD, trimethylalumi-
num (TMA) and water vapor are sequentially pulsed
through the reaction chamber.13 The number of cycles
was 830, which made obtaining a layer thickness of
about 120 nm possible. Layers of this thickness are
commonly used in the surface modification of metallic
biomaterials in contact with bone tissue. The variable
parameter was the temperature of the process. The
authors proposed the execution of the process at reduced
temperature of T = 150 °C and at an elevated tempera-
ture of T = 300 °C. All the samples were subjected to
examinations before the sterilization treatment in an
autoclave (T = 135 °C, p = 2,1 bar, t = 12 min).
2.1 Potentiodynamic test
Tests of resistance to pitting corrosion were carried
out for different variants of the surface treatment using
the potentiodynamic method. The study used VoltaLab®
potentiostat PGP 201 by Radiometer. The reference elec-
trode was a saturated calomel electrode (SCE), while the
counter electrode was platinum wire. The anode, on the
other hand, was cpTi+Al2O3/Ti6Al7Nb+Al2O3. The test
was performed in Ringer solution (250ml), supplied by
Baxter, at a temperature of T = 37 °C and pH = 6.8±0.2.
The study was initiated by indicating the open-circuit
potential EOCP. Then, recording of polarization curves
started from the potential Estart = EOCP – 100 mV. Samples
were polarized with scan rate of 0.16mV/s. Tests were
carried out for five samples of each kind of substrate.
Additionally, the Stern method was used to determine to
the value of the polarization resistance Rp.
M. BASIAGA et al.: COMPARISON OF THE PHYSICOCHEMICAL PROPERTIES OF Al2O3 LAYERS ...
638 Materiali in tehnologije / Materials and technology 51 (2017) 4, 637–641
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Table 1: Chemical composition of analyzed materials
cpTi, mass concentration, in mass fractions (w/%)
Element N C H Fe O Ti
ISO 5832-2 max. 0.05 max. 0.1 max. 0.0125 max. 0.5 max. 0.4 bal.
Certificate 0.03 0.05 0.005 0.4 0.4 bal.
Ti6Al7Nb, mass concentration, in mass fractions (w/%)
Element C H N O Ta Fe Al Nb Ti
ISO 5832-11 max. 0.08 max. 0.009 max. 0.05 max. 0.20 max. 0.50 max. 0.25 6.50–5.50 7.50–6.50 bal.
Certificate 0.008 0.003 0.03 0.08 0.37 0.22 6.24 6.84 bal.
2.2 Potentiostatic test
Evaluation of the resistance to crevice corrosion
made use of the potentiostatic method, recording
changes in the current density at +800mV potential for
15 min.14 The measurement system was identical to the
one used for potentiodynamic tests. The tests were
carried out in the Ringer solution (250 mL), supplied by
Baxter, at T = 37±1 °C and pH = 6.8 ±0.2.
2.3 Adhesion test
Adhesion of the Al2O3 film to the cpTi and Ti6Al7Nb
was evaluated with the use of a scratch test.15 During the
test a scratch was made with the use of Rockwell
diamond cone with gradual growth of the indenter’s
normal load. The critical force, a measure of adhesion, is
the minimum normal force causing the loss of adhesion
of the coat to the base. Evaluation of the critical force Lc
based on the record of changes in acoustic emission, fric-
tion force and friction coefficient as well as a microsco-
pic inspection with a light microscope, integrated with
the platform. Tests were performed at the loading force,
increasing from Fc = 0.03 N to 30 N and at the following
working parameters: loading rate vs = 100 N/min; table
travel rate vt = 10 mm/min, scratch length l = 3 mm.
2.4 Wettability test
Surface wettability and surface energy (SEP) were
evaluated with the use of the Owens-Wendt method. The
wetting-angle measurements used two liquids: distilled
water (w) (by Poch S.A.) and diiodomethane (d) (by
Merck). A measurement with a drop of the liquid and
diiodomethane, placed on the outer layer of the material,
was performed at the temperature T = 23 °C at the test
stand incorporating a goniometer SURFTENS UNIVER-
SAL by OEG and a computer with Surftens 4.5 software
to analyse the recorded drop image. Five drops of
distilled water and diodomethane were applied onto the
surface of each sample, each with capacity of 1.5 μL.
The measurement began 20 s after the application of the
drops. The duration of a single measurement was 60 s,
with the sampling rate of 1 Hz. Next, the determined
values of the contact angles  and the surface energy
were presented as mean values with a standard deviation.
3 RESULTS AND DISCUSSION
3.1 Potentiodynamic test
Polarization curves recorded for the substrates alone
and samples covered with an Al2O3 layer deposited at a
temperature of T = 150 °C and T = 300 °C for cpTi and
Ti6Al7Nb are shown in Figures 1 and 2. Based on the
received curves the characteristic values describing the
resistance to pitting corrosion were determined (Table 2).
Regardless of the type of substrate, a positive influence –
improving the corrosion resistance – of the Al2O3 layer
was established, as compared to baseline. An increase of
corrosion potential Ecorr and polarization resistance Rp
was found. An increase of the application process
temperature from 150 °C to 300 °C significantly reduced
the corrosion resistance of the Al2O3 layer (Table 2).
Table 2: The results of resistance to pitting corrosion test
Material Temperature Ecorr, mV Rp, M cm2
cpTi
Initial state -244 0.3
150 -147 7.5
300 -78 5.6
Ti6Al7Nb
Initial state -309 0.1
150 -155 5.1
300 -126 4.0
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Figure 2: Polarization curves for the modified Ti6Al7Nb alloy
Figure 1: Polarization curves for the modified cpTi
Figure 3: Examples of potentiostatic curves: a) cpTi in the initial state
and with deposited Al2O3 layer, b) Ti6Al7Nb in the initial state and
with deposited Al2O3 layer
3.2 Potentiostatic test
The test results of current density changes as a func-
tion of time in the test of resistance to crevice corrosion
indicate that regardless of the type of the substrate (cpTi,
Ti6Al7Nb), as well as the process temperature (150 °C,
300 °C) the Al2O3 layer is resistant to this type of corro-
sion (Figures 3a and 3b). The results confirmed the
formation of a compact Al2O3 oxide layer constituting a
barrier separating the substrate from the corrosive
environment in which the tests were performed.
3.3 Adhesion test
The results of the adhesion of the Al2O3 layer to the
metallic substrate were shown in Table 3 and Figures 4
and 5. The obtained results indicate the diverse adhesion
of Al2O3 to the ground with both cpTi and Ti6Al7Nb.
This is evidenced by the values of the individual para-
meters defined on the basis of the measurements. It was
found that a sample with Al2O3 deposited on the
Ti6Al7Nb surface shows better adhesion to the substrate
(Table 3). Additionally, the influence of the process
temperature on the adhesion of the analyzed layer, on
both cpTi and Ti6Al7Nb, was found. Slightly better
adhesion was observed in the case of the layer deposited
using the ALD method at the temperature T = 300°C,
regardless of the analyzed substrate material. During the
test there was no acoustic emission signal, which
indicates that the binding energy between the coating
and the substrate was too low.
Table 3: The results of scratch-test
Material TemperatureAl2O3 layer
Layer damages Critical forceFn, N
cpTi
150 °C
Crack Lc1 0.33
Delamination Lc2 1.02
300 °C
Crack Lc1 0.55
Delamination Lc2 1.14
Ti6Al7Nb
150 °C
Crack Lc1 1.32
Delamination Lc2 2.42
300 °C
Crack Lc1 1.20
Delamination Lc2 2.89
3.4 Wettability test
The wettability test results were presented in Table 4.
Based on the obtained results it was found that regardless
of the substrate used, the Al2O3 layer showed hydro-
phobic properties. The average value of the contact angle
for the Al2O3 layer, regardless of the temperature of the
deposition process, was equal to avg = 115°. On the
other hand, the cpTi and Ti6Al7Nb substrates showed
hydrophilic properties (avg = 61°).
Table 4: Wettability test results
Lp
Ti Ti6Al7Nb
Initial
state
(, °)
Al2O3
layer
(T = 150
°C)
(, °)
Al2O3
layer
(T = 300
°C)
(, °)
Initial
state
(, °)
Al2O3
layer
(T = 150
°C)
(, °)
Al2O3
layer
(T = 300
°C)
(, °)
1 56.9 118.2 116.8 68.2 117.8 112.5
2 58.1 109.7 124.3 65.3 114.0 107.2
3 57.8 111.8 121.8 66.9 119.7 117.0
4 CONCLUSIONS
In the ALD method, important parameters affecting
the quality of the final layer are the number of cycles and
the process temperature. Earlier works allowed the
authors to specify the number of cycles for depositing
layers with the best set of physicochemical proper-
ties.11,16–17 On this basis, the application of a Al2O3
coating on a titanium substrate (cpTi and Ti6Al7Nb) at
M. BASIAGA et al.: COMPARISON OF THE PHYSICOCHEMICAL PROPERTIES OF Al2O3 LAYERS ...
640 Materiali in tehnologije / Materials and technology 51 (2017) 4, 637–641
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 5: Examples of adhesion test results for the Ti6Al7Nb alloy
subjected to surface modification Al2O3 layer (T = 300 °C)
Figure 4: Examples of adhesion test results for the cpTi subjected to
surface modification Al2O3 layer (T = 300 °C)
temperatures of T = 150 °C and 300 °C was proposed.
The number of cycles used was Lc = 830. Based on the
results, a beneficial effect on pitting and crevice corro-
sion resistance of applied Al2O3 layer was determined,
compared to initial state, devoid of the layer, regardless
of the substrate used. The dependence was not shown
during the layer’s adhesion to the substrate test and the
wettability test. No significant influence of the depo-
sition process temperature on the obtained results was
found. Proposing the appropriate conditions for the
surface treatment using ALD method has promise and
will contribute to the development of technological pro-
cess with defined parameters of oxide layers manufac-
turing on implants used in bone surgery.
Acknowledgements
The publication was co-financed by the statutory
grant of the Faculty of Mechanical Engineering of the
Silesian University of Technology in 2015.
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