The document summarizes research on superhard nanocomposite Ti–Si–C–N coatings prepared using pulsed-d.c plasma enhanced chemical vapor deposition. Characterization of the coatings found they have a nanocomposite structure of nano-crystalline Ti(C,N) particles embedded in an amorphous matrix of Si3N4 and a-C. Hardness increases with Si and C content, reaching a maximum of 48 GPa. The coatings retain their hardness and nanostructure even after annealing up to 800°C, demonstrating high thermal stability. The formation of a nanocomposite structure contributes to the superhardness and thermal stability of the coatings.

1. Superhard nanocomposite Ti–Si–C–N coatings prepared
by pulsed-d.c plasma enhanced CVD
Dayan Ma, Shengli Ma, Kewei XuT
State-Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China
Available online 31 March 2005
Abstract
Ti–Si–N coatings have been investigated widely in recent years due to their unique nanocomposite microstructure and attractive
properties of superhardness, fairly good oxidation-resistance nearly to 1000 8C, etc. For this study, complex quaternary Ti–Si–C–N
coatings were deposited on HSS substrate at 550 8C using an industrial set-up of pulsed-d.c. plasma enhanced chemical vapor deposition
technique from TiCl4/SiCl4/H2/N2/CH4/Ar mixtures. The composition of the films could be controlled well through adjustment of CH4
flow rate and the mixing ratio of the chlorides. Detailed structural and chemical characterizations using transmission electron
microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) suggest formation of a Ti(C,N)/a-C/a-Si3N4
nanocomposite structure. Ti(C,N) films show (200) texture which change to random orientation of the crystallites when the silicon
content reaches about 9 at.%. Depth-sensing indentation measurement on coatings reveals that the hardness of coatings increases from
30 to 48 GPa with increasing Si and C content. These coatings show surprisingly high thermal stability and retain their hardness, even
after annealing to 800 8C.
D 2005 Elsevier B.V. All rights reserved.
Keywords: Ti–Si–C–N coatings; Nanocomposite; PECVD; Hardness
1. Introduction
TiN coatings have been widely used in mechanical
industry because of their high hardness and low coef-
ficient of friction [1,2]. However, some problems of TiN
coatings are still required to solve, for instance, its poor
mechanical and chemical stability at high temperature,
which is always present in tools and moulds fields, will be
a decisive disadvantage for TiN coatings [3,4]. In order to
improve the chemical and mechanical properties of the
TiN coatings used at elevated temperature, intensive
efforts have been made to explore multi-component
coatings such as Ti–Al–N, Ti–Si–N, Ti–B–N and Ti–C–
N in recent years [5–11]. Among them, Ti–Si–N nano-
composites coatings as a have attracted much more
interest because of their super- or ultra-hardness (40–105
GPa) and better stability at elevated temperature (nearly
up to 1000 8C) as well as higher elastic recovery (nearly
up to 80%) than TiN coatings.
In recent years, quaternary Ti–Si–C–N films deposited
by chemical vapor deposition (CVD) and reactive magnet-
ron sputtering [physical vapor deposition (PVD)] are
reported [12–17]. Based on our research, we feel that
pulsed-d.c. plasma enhanced chemical vapor deposition
(PECVD) is of great industrial importance because, like
PVD, it is a coating process that operates at relatively lower
temperature than CVD. Due to its good step-coverage
characteristics, the pulsed dc PECVD process is favorable
for mass production and suitably applicable to complex-
shaped tools and dies. The advantage of good step coverage
is that it is unique compared to other PVD techniques,
which all are more line sight of deposition processes and as
is traditional PECVD, and is especially important for
industrial applications.
In the present work, we give additional details on the
structural characterization of nanocomposite of Ti–Si–N
0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.surfcoat.2005.02.128
T Corresponding author. Tel.: +86 29 82668614.
E-mail address: kwxu@mail.xjtu.edu.cn (K. Xu).
Surface & Coatings Technology 200 (2005) 382–386
www.elsevier.com/locate/surfcoat

2. coatings prepared by pulsed dc PECVD in industrial-scale
chamber.
2. Experimental details
The Ti–Si–C–N coatings were deposited on high-speed
steel by a pulsed d.c. plasma enhanced chemical vapour
deposition. A schematic diagram of our PECVD deposition
system is shown in our earlier reference elsewhere [18]. The
processing conditions for depositing coatings are listed in
Table 1. TiCl4 was led to the chamber by the amount of
carrier gas (H2) flowing through the TiCl4 tank with
temperature kept constant at 40 8C. SiCl4 was led into
chamber from the SiCl4 tank at room temperature. The
coatings thickness was measured using scanning electron
microscopy (SEM) and elementary composition of Ti–Si–
C–N coatings was identified by EDX attached to the SEM,
X-Ray photoelectron spectroscopy (XPS) was used to
determine the chemical states of Si and C in Ti–Si–C–N
coatings, X-ray diffraction (XRD) using Cu-Ka radiation
was used to identify crystalline phases in the coatings. The
microstructure of Ti–Si–C–N was examined by transmission
electron microscopy (TEM). The hardness measurements
were done by means of an automated load-depth-sensing
instrument using Vickers diamond indenter. The indentom-
eter Fischerscope 100 equipped with a microscope and
possibility to program a series of indentation at different
lateral positions on the coatings was used at a load of 30 mN
in order to assure that the indenter depth does not exceed 5–
10% of the coating thickness. The hardness values obtained
from the Fischerscope was verified by measuring the size of
remaining indentation in SEM and calculating the hardness
from the equation H =0.927L /AP where L is the applied
load and AP is the projected area of indentation; Six points
for each specimen were completed and then got the average
value as hardness.
The thermal stability of coatings was evaluated by
annealing treatment, which was carried out in the atmos-
phere, which is ultra-pure N2, keeping 30 min at each
annealing temperature from 600 to 900 8C. There are steps
of 100 8C between 600 and 900 8C.
3. Results and discussion
The effect of the addition of CH4 and SiCl4 on the
overall elemental concentration was evaluated by EDX
and the results are shown in Table 2. In general, both the
carbon and silicon content in the coatings increased with
increasing flow rate of CH4 and SiCl4, respectively. For
Table 1
PCVD Ti–Si–C–N films processing conditions
Pulse voltage 650 V
Pulse-on time 25 As
Pulse-off time 25 As
Pressure 200–240 Pa
Deposition time 4 h
TiCl4 flow rate 2 sccm
SiCl4 flow rate 0.5–4.5 sccm
N2 flow rate 20 sccm
H2 flow rate 100 sccm
CH4 flow rate 0–30 sccm
Ar flow rate 3 sccm
Table 2
Hardness and composition of Ti–Si–C–N coatings
Sample No. CH4 flow
rate (ml/min)
SiCl4 flow
rate (ml/min)
Si Content
(at.%)
Ti Content
(at.%)
C Content
(at.%)
Cl Content
(at.%)
N Content
(at.%)
Hardness
(GPa)
1 0 15 13 48 0 0.8 38 38
2 60 5 3 58 4 0.6 35 32
3 100 8 6 53 7 0.6 34 38
4 170 8 4 55 10 0.5 30 36
5 170 15 12 50 8 0.9 29 42
6 270 5 2 46 11 0.5 42 30
7 310 8 3 51 15 0.6 30 34
8 350 12 9 42 24 0.8 25 45
9 400 15 10 38 30 0.9 20 48
20 30 40 50 60 70 80
α−Fe
[222]
[311]
[220]
[200]
2Θ(ο)
Intensity(a.u.)
α−Fe
TiC
TiN
[111]
sample 2
sample 6
sample 7
sample 9
Fig. 1. X-ray diffraction patterns of Ti–Si–C–N films with various Si and C
contents.
M. Dayan et al. / Surface & Coatings Technology 200 (2005) 382–386 383

3. instance, increasing the flow of CH4 from 0 to 400 ml/
min caused an increase of [C] from 0 to about 30 at.%.
Under constant the flow of CH4, the increasing of Si
content in coatings results from increasing of SiCl4 flow.
Also, from Table 2, one can see that the hardness of
coatings increase with increasing Si content and C
content, reaching a maximum value of about 48 GPa at
content of 10 at.% Si and 30 at.% C. In addition, we
determined that Cl content in coatings is less than 1 at.%.
The thickness of coatings was variable from 4 to 8 Am
and increased with increasing of Si and C content.
The XRD spectra of some selected samples are shown in
Fig. 1, revealing a crystalline structure of the Ti–Si–C–N
coating. The vertical lines indicate the strain-free peak
position from JCPDS powder diffraction database for TiN
(solid lines) and TiC (dashed lines). Sample 2 shows a
strong TiN [200] preferred orientation. The same crystalline
orientation was observed in samples 6 and 7, with system-
atic shift of the peaks towards lower 2 h values. This shift
can be attributed to a formation of the TiC crystalline phase,
which also exhibits very similar lattice parameters. With
increasing of Si content in coatings, the Ti–Si–C–N coating
has somewhat mixed orientations as shown by the intensity
distribution of [111], [220] and [200].
Additional information of evolution of the coating
chemical structure has been obtained from the analysis of
high resolution XPS spectra using peak assignments based
on literature data [19–23]. The C 1 s spectrum for Ti–Si–C–
N is presented in Fig. 2(b), which shows carbon bound as
Ti–C (281.3–282 eV) and C–C (284.1–284.6 eV), demon-
strating that some carbon atoms replaced nitrogen atoms in
TiN grains; the others existed as amorphous carbon in the
grain boundaries. The XPS analysis (Fig. 2a) also revealed
the existence of Si3N4 (Si 2p-102.6 eV). However, XRD
results did not show any crystalline Si3N4 phase, implying
that Si3N4 could be in amorphous form.
Furthermore, Fig. 3(a) (b) shows the micrographs of
transmission electron microscope (TEM) and selected area
and electron diffraction (SAED) patterns of coatings with
high C, Si content and low C, Si content, respectively. It can
be observed that the Ti–Si–C–N coatings are nanocomposite
coatings of nano-crystalline particles (black area) embedded
in amorphous matrix, which were clearly distinguished from
each other by SAED. Similarly, a mixture of nanocrystalline
294 291 288 285 282 279 276
Intensity(a.u.)
Binding Energy (eV)
Total
C-C
Ti-C
C-C
TiC(b)
114 112 110 108 106 104 102 100 98 96
Intensity(a.u.)
Binding Energy (eV)
Si3
N4
Si3
N4(a)
Fig. 2. XPS spectrum of the Si 2p and C1s of sample with high Si and C
content.
Fig. 3. Micrographs and diffraction patterns by transmission electron
microscope for Ti–Si–C–N coatings with (a) high Si and C content, (b) low
Si and C content.
M. Dayan et al. / Surface & Coatings Technology 200 (2005) 382–386384

4. and amorphous phases also formed in Ti–Si–C–N coatings
deposited by PVD system, however, an amorphous phase
formed as individual grains rather than as intergrain
amorphous layers [12]. For comparison, the Ti–Si–C–N
coatings prepared by CVD and PVD are single phase
expressed as (Ti,Si)(C,N), but not a composite coatings [14–
17]. For a deeply compared to the crystallite sizes change
directly with TEM micrograph in present different experi-
ential conditions, we can seen in Fig. 3 that the crystallite
sizes increase obviously from about 3–5 nm in sample with
high C, Si content up to about 30 nm in sample with low C,
Si content. This result illustrate that the crystallite sizes of
Ti(C,N) can be greatly refined by the additions of a certain
amount of Si and C.
Ti–Si–C–N nanocomposites show a surprisingly high
thermal stability, do not recrystallize even upon annealing to
800 8C and also do not change their room temperature
hardness after the annealing, as shown by one example from
a series of such measurements in Fig. 4. The crystallite size
was determined by Scherrer formula from the integral
widths of the XRD Bragg peaks. This result clearly shows
that high hardness of our coatings is not influenced by a
compressive stress induced in the films by energetic ion
bombardment.
Based on the analysis of the Ti–Si–C–N coating
microstructure, a higher micro-hardness of Ti–Si–C–N
coatings compared to TiN coatings can be explained by
their microstructural changes. Solution hardening and
work hardening do not operate in small nanocrystals
about V10 nm because solution atoms segregate to the
grain boundaries. Furthermore there are no dislocations in
such small crystallites. Therefore the explanation of
superhardness is the following: the combination of a hard
nanocrystalline Ti(C,N) having a grain size of V10 nm
with an amorphous phase, the latter having a sufficient
structural flexibility to form a strong interface and
suppress the grain boundary sliding. The formation of
harder TiC than TiN and solution hardening of C atom
may result in higher hardness of Ti–Si–C–N coatings than
that of Ti–Si–N coatings. Another question is why the
formation of nanocomposite coatings of high thermal
stability exists in Ti–Si–C–N system. In Ref. [24], Veprek
et al. gives an explanation to this interesting fact, they
suggest that nanocomposite coatings is based on thermo-
dynamically driven segregation in this system which
display immiscibility and undergo spinodal decomposition
even at high temperature.
4. Conclusions
In this work, nc-Ti(C,N)/a-C/a-Si3N4 coatings were
deposited by Pulsed-PCVD system in a industrial-scale
chamber which is very importance of industrial application.
Using a multitechnique characterization approach, we
determined that the coatings present a nanocomposite
structure formed by Ti(C,N) particles (about 3–30 nm in
diameter) incorporated in the Si3N4 and a-C matrix. With
increasing of Si and C contents in coatings, the Ti(C,N)
exhibits a mixed orientations of [111], [220] and [200]. The
microhardness of the coatings increases with increasing Si
content and C content, achieves a maximum value of about
48 GPa at the content of 10 at.% Si and 30 at.% C in the
coatings. The nanostructure of Ti–Si–C–N coatings and
resulting superhardness (measured at room temperature)
remain up to high temperatures of z800 8C.
Acknowledgements
The authors acknowledge the financial support of the Na-
tional Natural Science Foundation of China (No.50271053,
50371067), the International Key Joint—project of National
Natural Science Foundation (50420130033) and National
Key Basic Research and Development Program of China
(2004CB619302).
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