Resume In this report the effects of the substrate on the microhardness of Diamond like carbon (DLC) thin films were investigated. The DLC coatings were deposited by Radio Frequency Plasma Actived Chemical Vapor Deposition (RF PACVD; 13,56 MHz) process on three mechanically polished substrates, which were chosen for comparison; hardened molybdenum high speed steel AISI M2, unhardened tool steel AISI L2 and titanium alloy TiAl6V4. The aim of the present investigation was to determine the influence of substrates on microhardness and other mechanical properties of DLC layer. These properties especially microhardness were studied and compared from nanoindentation load -displacement curves. Results show that the hardness of the substrate is the crucial value for the hardness of the DLC films

D Tischler

I Štěpánek

P Vlčák

Z Budinská

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D. Tischler, Z. Budinská, P. Vlčák, I. Štěpánek: Nanoindentation test for DLC coating analysis 
 
 
Materials Engineering - Materiálové inžinierstvo 18 (2011) 105-109 
 
105 
NANOINDENTATION TEST FOR DLC COATING 
ANALYSIS 
 
Daniel Tischler 1*, Zuzana Budinská 1, Petr Vlčák1, Ivo Štěpánek2 
 
1 Department of Physics, Faculty of Mechanical Engineering, CTU in Prague, Technicka 4, 16607  
  Prague, Czech Republic 
2 Department of Materials Science,University of West Bohemia, Veleslavinova 11, 301 14 Plzen,  
  Czech Republic 
* Corresponding author: Tel.: +420 2 2435 2432, e-mail: daniel.tischler@fs.cvut.cz 
 
 
Resume 
In this report the effects of the substrate on the microhardness of Diamond 
like carbon (DLC) thin films were investigated. The DLC coatings were 
deposited by Radio Frequency Plasma Actived Chemical Vapor Deposition  
(RF PACVD;  13,56 MHz) process on three mechanically polished 
substrates, which were chosen for comparison; hardened molybdenum high 
speed steel AISI M2, unhardened tool steel AISI L2 and titanium alloy 
TiAl6V4. The aim of the present investigation was to determine the 
influence of substrates on microhardness and other mechanical properties 
of DLC layer. These properties especially microhardness were studied and 
compared from nanoindentation load – displacement curves.  Results show 
that the hardness of the substrate is the crucial value for the hardness of the 
DLC films.  
 
 
 
Available online: http://fstroj.uniza.sk/PDF/2011/18-2011.pdf 
 
Article info 
Article history: 
Received 3 May 2011 
Accepted 19 August 2011 
Online 2 September 2011 
 
Key words:  
PACVD  
DLC 
Microhardness 
Nanoindentation 
Coating 
Substrate 
 
 
ISSN 1335-0803 
 
1. Introduction 
Diamonds like carbon (DLC) films have 
received considerable interest for more than a 
decade because of their excellent tribological 
properties such as low-friction coefficient, high 
wear resistance and high hardness [1]. 
Applications were reported for numerous high 
precision components and tools. One problem is 
their poor adhesion on steel substrates without 
intermediate layers. The mechanical and 
tribological properties of pure DLC films like 
hardness and wear resistance are superior to 
those of metal-containing carbon hydrogenated 
films (Me-C:H). However, the productivity of 
the deposition process is not as good because  
Me-C:H can be deposited by well known 
Physical Vapor Deposition (PVD) methods like 
magnetron sputtering. The most common method 
for depositing pure DLC films is Radio 
Frequency Plasma Actived Chemical Vapor 
Deposition (RF PACVD; 13,56 MHz) which is 
known to be technically difficult and expensive 
to scale up to industrial dimensions [2].  
The classical microhardness is determined 
by the resistance to local deformation by a hard 
diamond indenter, pressed into the material.       
A fast development in the analysis methods is 
appearing at this time. Improved methods could 
help solving many technical problems. Whereas 
indentation methods are used for evaluating 
some mechanical properties, such as 
nanohardness, adhesive and cohesive behavior, 
wear resistance and fracture. Their big advantage 
is that they can be used for analyzing surfaces of 
real components or tools, which then do not have 
to be cut. However, knowledge of the true 
D. Tischler, Z. Budinská, P. Vlčák, I. Štěpánek: Nanoindentation test for DLC coating analysis 
 
 
Materials Engineering - Materiálové inžinierstvo 18 (2011) 105-109 
106 
hardness of the thin film with a thickness of 
1 µm or less continues to be a quite a challenge. 
The nanoindentation offers a solution for this 
problem.   
The nanohardness can be measured 
directly on the tool surface without breaking the 
surface, because the indentation is too small to 
cause any damage. The indentation 
microhardness measurement is a simple, 
reproducible, and cheap method, which is often 
used for the characterization of surface for 
mechanical applications. Measuring the elastic 
and plastic properties of thin films is always the 
first critical step to analyze their mechanical 
integrity and among alternative techniques, 
nanoindentation is arguably the simplest 
approach for measuring the mechanical 
properties of small material structures including 
thin films [3,4]. For indentation loading of a 
typical elastic and hard thin film on a ductile 
substrate, the mode of deformation of the film is 
assumed to be controlled by the plastic 
deformation of the underlying substrate [5-8]. 
Bending and stretching of the film due to 
yielding of the substrate induce stresses that lead 
to fracture in the brittle film [1]. Analysis DLC 
coating from nanoindentation load – 
displacement curve has not been yet described in 
details. As well it is very important to know 
behavior of substrates of thin films. The general 
aim of the present investigation was to determine 
the influence of substrates on microhardness and 
other mechanical properties of layers. That aim 
was achieved by help of nanoindentation tests. 
 
2. Experimental  
2.1 Choice of materials  
There were three materials (substrates) 
chosen for experiment. First material was high 
molybdenum speed steel for cold work 
applications AISI M2 which is useful for 
example for tools, punching, forming and 
pressing, etc. 
 Table 1 
Average concentration of materials 
 AISI M2 AISI L2 TiAl6V4 
Al - - 6 
C 0,8-1 0,4 -1  
Mn 0,2-0,4 0,1-0,9  
Si 0,35 0,5  
P 0,03 0,03  
S 0,03 0,03  
Cr 3,8-4,5 0,7-1,2  
Mo 5 0,25  
W 6 -  
V 1,8-2,2 0,1-0,3 4 
Ti - - rest 
 
Unhardened low-alloy special-purpose tool steel 
AISI L2 was chosen as second material.  
Materials AISI M2 and AISI L2 have a suitable 
combination of wear resistance, toughness and 
compressive strength. Titanium alloy TiAl6V4, 
which is very unique material for biomedical 
applications, was chosen as third substrate.  
Table 1 shows the average concentration of 
above mentioned materials. The substrates with 
size 20 mm in diameter × 5 mm in thickness 
were polished prior to deposition to a surface 
roughness in the range of Ra = (0,02 – 0,03) µm.  
  
2.2 Deposition process  
Amorphous carbon films were deposited 
in a PACVD apparatus, which is shown in Fig.1. 
The chamber was 110 mm in diameter and 970 
mm in long. Before loading in the chamber the 
polished substrates were chemically cleaned with 
acetone and isopropyl alcohol respectively in 
ultrasonic bath for 15 min. Then the samples 
were dewatered very carefully and they were 
loaded into the reaction chamber and mounted on 
working electrode.  
D. Tischler, Z. Budinská, P. Vlčák, I. Štěpánek: Nanoindentation test for DLC coating analysis 
 
 
Materials Engineering - Materiálové inžinierstvo 18 (2011) 105-109 
 
107 
Fig. 1. A Schema of RF PACVD (13,56 MHz) 
equipment 
The substrates were additionally cleaned 
in argon and then in nitrogen discharge at 0.16 
Torr and 0.20 Torr respectively by Direct 
Current Plasma Actived Chemical Vapor 
Deposition (DC PACVD) plasma in order to 
remove impurities. For improvement of adhesion 
we decided to dope to introduce both silicon and 
nitrogen into carbon layers. Silicon was 
introduced from Hexamethyldisiloxane 
(HMDSO) - 98 % purity.  
Methane was chosen as precursor for 
carbon deposition. So, the gas mixture of CH4 
(30 sccm), HMDSO (0.5 g/h ) and N2 (15 sccm) 
was introduced into RF PACVD reactor. The 
total work gas pressure was 1 Pa and during the 
deposition processes the total pressure was held 
constant. The applied RF 13,56 MHz power 
input was kept at 200 W. The process parameters 
such as pressure and gas flows were controlled 
by mass flow controllers and the pressure was 
controlled by a butterfly valve independently of 
the total gas flow.  
A DLC films thickness of 1,3 µm was 
achieved after 35 minutes of RF PACVD 
deposition.  
 
2.3 Nanoindentation 
Determination of micro-hardness of the 
coatings has been carried out by nanoindentation. 
In this study, Vickers nanoindentation tests using 
the nanoindenter Shimadzu DUH 202 (mode 2) 
equipment were performed. This equipment had 
a Vickers shaped diamond tip with load 
resolution of 0.1 mN. Distinguishing resolution 
is 0.2 nm. Microhardness was calculated from 
the load-displacement curves using an analysis 
program. The specimen was put on the horizontal 
holder with a microscope directly located above 
the selected area. The conditions of the 
measurement are following: at a room 
temperature (25°C) and at a relative humidity 
around 55 %. The displacement during loading 
gives the so-called dynamic hardness HD, which 
is expressed by the following equation: 
2
max
.43,26 h
F
H D =  ,    (1) 
where Fmax  is the peak indentation load and h is 
the indenter penetration depth at Fmax.   The load 
– displacement experiments were repeated on 2 
independent locations of the surface of each 
specimen. 
 
3. Results  
In Vickers nanoindentation test, the 
following three samples were used. 
Measurements were performed gradually under 
the maximum load of 200g to obtain the 
microhardness values occurring on the top of the 
surface of the substrate under the thin film, and 
under 25g load to obtain the microhardness 
values occurring near the borderline of the thin 
film and the substrate as well as under the load of 
5g and 2g to obtain the microhardness values 
particularly on the surface. Microhardness was 
calculated along formula (1). 
The load/unload displacement curves for 
three different samples are shown in Fig. 2. This 
figure shows record of dependence of depth of 
D. Tischler, Z. Budinská, P. Vlčák, I. Štěpánek: Nanoindentation test for DLC coating analysis 
 
 
Materials Engineering - Materiálové inžinierstvo 18 (2011) 105-109 
108 
indent on the load during nanoindentation 
investigation of coating hardness. In this case the 
maximal loading 200 g was used. The 
microhardness was highest at speed steel AISI 
M2. Microhardness of system substrate-coating 
for AISI M2 is approximately 900 DHV, for 
AISI L2 is approximately 370 DHV and for 
TiAl6V4 is approximately 300 DHV. 
___ AISI M2 
___ AISI L2 
___ TiAl6V4 
 
 
Fig. 2. Nanoindentation load-displacement 
curves of DLC films. Max. load 200 g was used 
(full colour version available online) 
The nanoindentation of curve with a 
maximal load 25 g (Fig.3) has a typical behavior 
during the nanoindentation test. Curves 
demonstrate higher microhardness than at 200 g 
load/unload. The microhardness was again 
highest at speed steel AISI M2.  Microhardness 
of system substrate-coating for AISI M2 is 
approximately 1170 DHV, for AISI L2   is 
approximately 480 DHV and for TiAl6V4 is 
approximately  300 DHV. 
In Fig. 4 is shown at further load reduction 
by a maximum of 5 g a share of substrate goes 
down, although it is marked. The highest 
hardness and further rising elastic deformation is 
shown in the first specimen (AISI M2) though it 
is smaller difference between steel AISI M2 and 
steel AISI L2. 
In the other two specimens there is still a 
strong plastic deformation. A higher hardness is 
in the second specimen but a stronger elastic 
deformation is in the third specimen.  
Microhardness of system substrate-coating for 
AISI M2  is approximately 1180 DHV, for AISI 
L2 is approximately 750 DHV and for TiAl6V4 
is approximately 480 DHV. 
___ AISI M2 
___ AISI L2 
___ TiAl6V4 
 
 
Fig. 3. Nanoindentation load-displacement 
curves of DLC films In this case the maximal 
loading 25 g was used 
(full colour version available online) 
___ AISI M2 
___ AISI L2 
___ TiAl6V4 
 
 
Fig. 4. Nanoindentation load-displacement 
curves of DLC films. In this case the maximal 
loading 5 g was used 
(full colour version available online) 
___ AISI M2 
___ AISI L2 
___ TiAl6V4 
 
 
Fig. 5.  Nanoindentation load-displacement 
curves of DLC films. In this case the maximal 
loading 2 g was used 
(full colour version available online) 
D. Tischler, Z. Budinská, P. Vlčák, I. Štěpánek: Nanoindentation test for DLC coating analysis 
 
 
Materials Engineering - Materiálové inžinierstvo 18 (2011) 105-109 
 
109 
In Fig. 5 is shown registration of 
dependence of depth of indent on the load/unload 
during nanoindentation investigation of coating 
hardness at the maximal loading 2 g. A growth of 
elastic deformation of surface layers is still 
manifested with next decline of a standard load 
to 2 g.  It was seen that all the data points are 
almost identical. The 2g load ensures that the 
substrate has minimal influence on the 
microhardness of the system substrate-film. All 
specimens, strictly speaking all films show 
evident elastic deformation. Although the 
influence of substrate is reducing, is still evident 
influence of substrate.  
Microhardness of system substrate - 
coating for the specimen AISI M2 is 1460 DHV, 
for AISI L2 is 1000 DHV and for TiAl6V4 is 
850 DHV. 
4. Conclusions 
We achieved DLC solid lubricant coatings 
by RF PACVD technology on three various 
substrates.  The roughness of the coatings in the 
range Ra = (0,02 -0,03) µm, was approximately 
the same as the roughness of the substrate. The 
thickness of coatings was 1300 nm. The 
nanoindentation load-displacement curves of thin 
DLC films were determined using 
nanoindentation with Vickers diamond indenter, 
specifically by equipment nanoindentor 
Shimadzu DUH 202.  The coatings DLC were 
adherent, hard and wear resistant. 
 The loading part of the curve is a 
combination of elastic and plastic 
deformation, while the unloading curve is 
mainly dominated by the elastic deformation. 
Analyses of the loading curves are 
demonstrated by the significant dependence 
on the hardness of the substrate.  
 The microhardness of all coatings increased 
with decreasing penetration load.  In order 
words, influence of the substrate descends 
with the decline of the load, especially in the 
case, when the load/unload is extremely 
small, 5 g or 2 g. This verification is evident 
from records.  It is obvious that the distance 
of single maximum decreases with 
decreasing load/unload.  
 The hardened high speed steel AISI M2 
shows more elastic deformation than the 
other materials. A significant plastic 
deformation is shown in the second 
specimen (unhardened tool steel AISI L2) 
and third titanium alloy specimen TiAl6V4. 
  Finally, the microhardness values and 
elastic-plastic behavior of DLC system are 
significantly influenced by hardness of the 
substrates.  
Acknowledgement 
This research received support under Grant 
No. MSM 6840770012 of the Czech Republic 
Ministry of Education project “Trandisciplinary 
research in Biomedical Engineering II”. Authors 
gratefully acknowledge this support. 
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NANOINDENTATION TEST FOR DLC COATING ANALYSIS

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NANOINDENTATION TEST FOR DLC COATING ANALYSIS

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