In this study, diamond coating adhesion on cobalt-cemented tungsten-carbide (WC-Co) substrates was investigated using scratch testing. In particular, the methodology was applied to evaluate the effects of the coating thickness and interlayer on coating delaminations. In the coating thickness effect study, substrate surface preparations, to remove the surface cobalt, prior to diamond depositions was common chemical etching using Murakami solutions. On the other hand, to study the interlayer effect, by halting the catalytic effect of the cobalt binder, two different interlayers, Cr/CrN/Cr and Ti/TiN/Ti, were deposited to WC-Co substrate surfaces (no chemical etching) by using a commercial physical vapor deposition (PVD) system in a thickness architecture of 200nm/1.5µm/1.5µm, respectively. Diamond films were synthesized by using a hot-filament chemical vapor deposition (HFCVD) reactor at a gas mixture of 6 sccm of CH4 and 60 sccm of H2, with varied deposition times. Scratch testing was conducted on the fabricated specimens using a commercial machine, at a maximum normal load of 20 N and a speed of 2 mm/min. It is noted that the onset of coating delamination can be clearly identified by high-intensity acoustic emission (AE) signals when such events occur, which can be used to determine the critical load. Scratched track geometry was also characterized by scanning electron microscopy. The results show that the adhesion of the diamond coating increases with the increased coating thickness, with a nearly linear relation, in the range tested. For the two types of interlayer materials tested, either of them seems to be effective and the diamond coating with Ti-interlayer shows poorer adhesion comparing to the Cr-interlayer coating.

1.
1
Coating Thickness and Interlayer Effects on CVD-diamond Film Adhesion to Cobalt-
cemented Tungsten Carbides
Ping Lua
, Humberto Gomezb, d
, Xingcheng Xiaoc
, Michael Lukitschc
, Delcie Durhamb
, Anil
Sachdevec
, Ashok Kumarb
, Kevin Choua
a
Mechanical Engineering Department, University of Alabama, Tuscaloosa, AL 35487, USA
b
Department of Mechanical Engineering, University of South Florida, Tampa, FL 33620, USA
c
Chemical Sciences & Materials Systems Laboratory, General Motors R&D Center, 30500
Mound Road, Warren, MI 48090, USA
d
Departamento de Ingeniería Mecánica, Universidad del Norte, Barranquilla, Colombia
Abstract
In this study, diamond coating adhesion on cobalt-cemented tungsten-carbide (WC-Co)
substrates was investigated using scratch testing. In particular, the methodology was applied to
evaluate the effects of the coating thickness and interlayer on coating delaminations. In the
coating thickness effect study, substrate surface preparations, to remove the surface cobalt, prior
to diamond depositions was common chemical etching using Murakami solutions. On the other
hand, to study the interlayer effect, by halting the catalytic effect of the cobalt binder, two
different interlayers, Cr/CrN/Cr and Ti/TiN/Ti, were deposited to WC-Co substrate surfaces (no
chemical etching) by using a commercial physical vapor deposition (PVD) system in a thickness
architecture of 200nm/1.5µm/1.5µm, respectively. Diamond films were synthesized by using a
hot-filament chemical vapor deposition (HFCVD) reactor at a gas mixture of 6 sccm of CH4 and
60 sccm of H2, with varied deposition times.
Scratch testing was conducted on the fabricated specimens using a commercial machine,
at a maximum normal load of 20 N and a speed of 2 mm/min. It is noted that the onset of coating
delamination can be clearly identified by high-intensity acoustic emission (AE) signals when
such events occur, which can be used to determine the critical load. Scratched track geometry
was also characterized by scanning electron microscopy.
The results show that the adhesion of the diamond coating increases with the increased
coating thickness, with a nearly linear relation, in the range tested. For the two types of interlayer
materials tested, either of them seems to be effective and the diamond coating with Ti-interlayer
shows poorer adhesion comparing to the Cr-interlayer coating.

2.
2
1. Introduction
1.1. CVD diamond coated tools
The Chemical Vapor Deposition (CVD) synthesis of diamond on cemented carbides has
been an ideal approach in enhancing cutting tools life and improving their machining
performance due to the exceptional diamond properties such as superior hardness, low
coefficient of friction, and chemical stability. CVD diamond-coated tools provide significant
advantages in terms of cost and flexibility when compared to synthetic polycrystalline diamond
(PCD) tools [1], which are also commonly used in the manufacturing industry. The ability to
form a conformal coating on the tool surface, the relative simplicity of the synthesis as a result of
the new advances in industrial CVD reactors, and the possibility to produce different film
structural characteristics (micro or nano-crystalline), represent a significant advantage of CVD
diamond coatings [2]. However, under cutting operations represented by harsh machining
conditions or high-strength workpiece materials, the diamond coating delamination remains to be
the primary wear mechanism that results in catastrophic tool failures [3]. In cemented carbide
substrates like WC-Co, diamond delamination is due to the insufficient adhesion between the
coating and the substrate, partially as the result of the formation of non-diamond compounds at
the substrate-diamond film interface due to the Cobalt-carbon interdifussion at CVD deposition
temperatures.
1.2. Interface engineering
Several interface engineering approaches have been reported in the last 15 years with the
aim to reduce the undesired catalytic effect of cobalt on diamond adhesion [4-6]. In order to
maximize the practical adhesion of diamond coatings on cemented carbides, any approach must
halt the interdifussion effect of cobalt. The most widely successful techniques discussed in the
literature are related to the cobalt removal in depths ranging in about 3 to 10 µm from the
substrate surface by using chemical etching methods [7], or by halting the cobalt effect on the
surface by depositing interdifussion barrier layers [8], that also diminish the thermal stresses
caused during the diamond growth.
Interface engineering techniques are specifically targeted to improve the diamond coating
adhesion. Since an increased surface roughness has been correlated in enhancing the diamond

3.
3
nucleation density and promoting a film interlocking behavior, surface pretreatment efforts can
be also tailored accordingly besides suppressing the cobalt catalytic effects. In addition to the
improvements in the diamond growth conditions, the substrate surface plays an important role in
the final adhesion behavior of diamond coatings. Surface textures and surface/subsurface damage
characteristics on the substrate have a direct impact to the subsequent diamond adhesive quality
and wear failure modes; hence the final diamond coating adhesion behavior depends on the
surface pretreatments used and their resulting effects on the substrate surface, which are
ultimately the interface characteristics in the substrate-coating composite system. This interface
requires the formation of strong interfacial chemical bonds between the diamonds crystallites
nucleated at the surface and the atoms at the substrate surface. Moreover, a mechanical
interlocking effect is also desired in order to enhance the coating addition.
The effects of chemical etchings on the surface characteristics of WC-Co substrates have
been studied by far [9, 10] and represent the pretreatment method used in most of the
commercial diamond coated cemented carbides in the industry. This method has the purpose to
produce a selective etching of the cobalt binder by using a two step process composed by an
initial wet treatment in a Murakami solution with the aim of reconstruct and rough the surface by
attacking the WC grains and exposing the Co binder [9]. Then, a second wet etching in an acid
solution (H2SO4 or HNO3 with H2O2) is used to reduce the exposed cobalt in a depth determined
by the etching time [10].
Another approach to avoid the catalytic effect of cobalt is the deposition of carbide and
nitride intermediate layers (CrN, TiN, TiC, SiC, AlN, etc) on the substrate before the final
diamond deposition. These interlayers normally deposited by physical vapor deposition (PVD)
methods must remain stable during the diamond deposition, have a low thermal expansion
coefficient to minimize internal stresses, and provide a carbide formation layer to improve
diamond nucleation [11]. These conditions may also be improved by using nanometer sized
metal thin layers like Cr and Ti at the top or bottom of the interlayer architecture. Additional
diamond particles may be peened in the top interlayer surface to provide additional diamond
nucleation sites and serve as anchors to the final diamond coating [12].
1.3. Coating adhesion and scratch testing

4.
4
There are several methods commonly used to examine the adhesion of coatings in general
[13]. Scratch testing is one of the most practical approaches in evaluating the adhesion of a hard-
thin coating on a particular substrate [14, 15], since it is reliable, simple to perform, and with no
special specimen geometry or preparation requirements. Coating adhesion is measured as a
correlation between the occurrences of critical load at the coating failure instant. In the event of
an adhesive failure, this critical normal load is taken as a measure of the coating–substrate
adhesion or used to calculate the work of adhesion [16, 17]. During a scratch test, a spherical
indenter tip slides over the surface of the coating to generate a groove under incremental or
constant normal load modes. In addition, the tangential force is measured during the test and the
morphology of the scratches can be observed simultaneously or afterwards, an acoustic emission
sensor is used to capture the coating delamination during scratch tests. When the resolved
compressive mean stress exceeds a critical value, the coating detaches from the substrate
decreasing the elastic energy stored in the coating [18]. Then, the work of adhesion at the
interface between the coating and substrate is equal to the energy release rate from coating at the
instant of detachment as a function of the compressive mean stress of the coating stress over the
delaminating area. Thus, the critical compressive coating mean stress responsible for the
detachment could be a measure of coating–substrate adhesion. On the other hand, diamond
coatings are very brittle. While a coating can withstand compressive stresses induced by the
indenter to a certain extent, it may fracture if a high tensile or shear stress field is induced
simultaneously, in particular, at the interface such as delamination. It is known that coating has a
higher critical compressive stress than tensile and shear stress, but less than the critical
compressive stress may result in coating delamination during scratch test.
1.4. Adhesion characterization
As discussed, the adhesion of coating is measured by the critical load under coating
failures, and there are different ways to determine the critical load determination [19].
Microscopic observation is the most reliable method to detect the coating delamination. This
technique can distinguish cohesive failure within the coating and adhesive failure at the interface
of the coating-substrate composite system. The use of acoustic emission (AE) sensors, which is
insensitive to mechanical vibration frequencies of the instrument, represents another option to
detect the elastic waves generated as a result of the formation and propagation of micro-cracks in

5.
5
diamond coating along to the tangential force (Ft) values recorded from force fluctuations along
the scratch. The adhesion of CVD diamond coating on molybdenum substrates has been
investigated by scratch testing [11], and results displayed critical normal load values in the range
of 16 to 40 N for CVD diamond films grown after 4 h at a CH4/H2 ratio of 0.5%. However,
diamond films grown after 24 h at a methane concentration of 0.5% do not exhibit any failure
when the force increased to75 N. Moreover, adhesion scratch tests were able to provide a direct
qualitative comparison of the adhesion of diamond coatings on steel and copper substrates [12],
with the aim to investigate the effect of metal substrates (copper and steel) and film thickness on
the adhesion, and these results showed that the diamond coatings on steel exhibits a higher
critical load than on the copper, but thicker films displays a higher critical load than thinner films
for the same kind of substrates.
1.5. Objectives and Approaches
This study aims at better understanding the adhesion of diamond-coated carbide tools by
micro-scratch testing, and the critical load for coating delamination were used to evaluate the
adhesion of diamond-coated carbide tools, where corresponding process singles would help to
identify the coating delamination. It is essential to investigate that the effect of coating thickness
and interlayer on the adhesion of the diamond coating to better understand the adhesion of
diamond-coated carbide tools.
2. Experimental details
2.1. Substrate preparation
Experimental samples correspond to WC-Co (6%) square cemented carbide substrates.
The surfaces of the tools display surface characteristics represented by feed marks resulting from
their manufacturing process. These preferential marks are depicted in Figure 1 and constitute the
as-receive state of samples before any surface pretreatment.
The use of chemical etching pretreatment and the pre-deposition of interdiffussion barrier
layers were applied to the samples with the aim to modify the as ground surface before the final
diamond deposition, improving the coating adhesion by halting the effect of the cobalt binder in

6.
6
the cemented carbide substrate. The conditions of the pretreatments are summarized in Table 1
and were selected from previous work of the authors [10].
2.2. Interlayer preparation
Two different interlayers, Cr/CrN/Cr and Ti/TiN/Ti were deposited to the WC- Co (6%)
substrate surface by using a commercial PVD coating system in thickness architecture of
200nm/1.5um/1.5um, respectively. This physical barrier prevents the diffusion of carbon into the
underlying cobalt phase and the subsequent graphite formation that is so deleterious to diamond
film adhesion. The barrier also provides a stress relaxation barrier layer [20]. Additional
treatments after the interlayer were applied to the top of the surface in order to improve the
surface roughness and diamond nucleation. This surface treatment corresponds to an additional
shoot peening to the final Cr and Ti using diamond powder particles (1μm).
2.3. Coating deposition
Pretreated samples were subjected to a seeding process prior diamond deposition. The
seeding method was performed using a slurry solution, consisting of 1.2 grams titanium
nanopowder, 1.2 grams nanocrystalline diamond powder, and 100 milliliters of methanol.
Diamond films were synthesized by using a HFCVD reactor at a pressure of 20 Torr, two
filaments located at the top of the sample operating at 90 V, and a gas mixture of 6 sccm of CH4
and 60 sccm of H2. In order to investigate the effect of coating thickness on the adhesion of
diamond coating, three different coating samples (coded T-1.5, T-2.5 and T-4.5) were prepared
under the same working parameters except the deposition time for the coating, which will result
in the thin coating thickness ranged from 1.5µm to 4.5 µm. Table 2 shows the sample details for
the diamond coated inserts used in the scratch tests detailed below. For the specimens with either
the Ti or Cr interlayer, the deposition thickness estimated was about 3 μm.
2.4. Scratch test setup, procedure and data acquisition
A Micro-scratch tester from CSM Instruments, model Micro-Combi, was used for the
experiments at room temperature, by using an indenter with tip radius of 50 µm, and a scratch
speed of 2 mm/min with a progressive loading method in order to determine the critical load for
the diamond-coated tools. The scratch length for each test was set to 5 mm. During the scratch

7.
7
test, tangential forces values, acoustic emission (AE) signals, and the resulting depth of the
scratch were acquired. A KEYENCE digital microscope (VHX-600X) was used to observe the
scratch marks and coating delamination after the test. In addition, a white-light interferometer
(WLI) was used to characterize the morphology of the scratch grooves, and a scanning electron
micrograph instrument (Philips XL30) was used to show how the coating delamination appear
and propagate.
3. Results and Discussion
3.1. Characterization information of different interfaces and diamond coatings
Raman spectroscopy was performed to all CVD diamond samples, corresponding to a
microcrystalline diamond structure represented by the 1332 cm-1
broad peak observed in the
Raman spectra and shown in Figure 2. The crystal structure of the diamond film correspond to
faceted (100){111} polycrystals was shown in Figure 3.
3.2. Scratch test results for diamond coated WC with different thicknesses
Scratch tests conducted on sample T-1.5 included four repeated tests of maximum load of
10 N, three repeated tests of maximum load of 30 N and one test of maximum load of 20 N.
Figure 4 shows the overall images of 8 scratch grooves at the corresponding load (1~4: 10 N,
5~7: 30 N, and 8: 20 N).
Figure 5 shows the AE signal and tangential force (Ft) vs. the applied normal load (Fn)
during the 4th scratch test with a progressive load of maximum 10 N. It is observed that the
tangential force increases smoothly, though varies slightly until reaching 10 N. It is also found
that only a few isolated high peaks (i.e. Spot 1) of AE signals exist before the normal force reach
10 N. This implies coating delamination may not initiate under such a load.
To understand the isolated high peaks, spot 1, the scratch groove was observed in the
digital microscope at 1000X after testing. From the correlation between the load and the distance,
the location corresponding to Spot 1 can be examined to verify whether the coating delamination
has initiated at that point. Figure 6a) shows the digital microscopic image at Spot 1 and the
corresponding normal load is around 8.0 N. It can be seen that the cracks on the coating have
been formed at the spot without coating delamination. Figure 6b) shows the digital microscopic

8.
8
image at the end of scratch test. It is shown that intensive cracks have been formed at the end of
scratch trace; however, no coating delamination is associated with them.
Figure 7 shows the AE signal and tangential force (Ft) vs. the applied normal load (Fn)
during the test with maximum load of 20N. Similar results are found that the tangential force
increases smoothly with the normal force less than 9 N, but follows with considerable variation.
An abrupt amplitude increase of AE signals (Spot 1) exists at the load around 9 N, followed by a
series of continuous high-amplitude AE peaks. In addition, the highest amplitude of AE peak
occurred at Spot 2, and drastic variation of tangential force was observed at Spot 2 with
corresponding normal force of 13 N.
Figure 8a) and 8b) show the digital microscopic image at Spot 1 and Spot 2, with the
corresponding normal load for Spot 1 around 9 N, and cracks initiation but without coating
delamination is found at such a force. The corresponding normal load for Spot 2 is around 13 N.
Coating delamination has initiated at such a force, with clearly exposing the substrate layer of
WC, near Spot 2. Figure 10c) shows the digital microscopic image at the end of scratch test. It is
shown that coating delamination continued, once initiated, to the end of the final load, with a
comparable delamination width. Figure 9 displays the SEM image for the coating delamination
(Spot 1) at 200X and 800X, it could be clearly seen that multiple micro-cracks existed on the
coating surface before Spot 1, followed with coating material removal from the substrate, where
coating delamination formed.
Sample results of testing on the sample T-4.5 with a maximum load of 20N, repeated
three times, are discussed below. Figure 10 shows the AE signal and tangential force (Ft) vs. the
applied normal load (Fn) during the 1st scratch test with maximum 20 N, similar to previous
observations, the transition with Spot 1 is found for the normal load of 14.6 N. and an abrupt
amplitude increase of AE signals (Spot 1) exists at the spot, followed by a series of continuous
high-amplitude AE peaks, implying the critical load for coating delamination.
Figure 11a) shows the digital microscopic image at Spot 1 with corresponding normal
load around 14.6 N. Coating delamination has initiated at such a force with clear exposing
substrate layer of WC, near Spot 1. Figure 11b) shows the digital microscopic image at the end

9.
9
of scratch test. It is shown that coating delamination continued, once initiated, to the end of the
final load.
Figure 12 shows the SEM images at the final load locations (20 N) on the three samples;
all the results confirmed that coating spallation along the scratch formed, and severe coating
detachment were found at the end of the scratch. It was also found that T-4.5 had the slightest
coating detachment comparing to the other two samples.
Figure 13 shows the result of the critical load of coating delamination vs. the coating
thickness. It can be noted that the critical load increases with the coating thickness, increasing
from 11.2 N to 14.5 N for the coating thickness of 1.5 μm vs. 4.5 μm. It demonstrates that the
adhesion of the diamond coating will increase with the coating thickness, for the range of this
study. Such an effect has been confirmed by other researchers [21].
3.3 Scratch test results on diamond coating with different interlayers
Figure 14a) and b) show the AE signal and tangential force (Ft) vs. the applied normal
load (Fn), with maximum 5 N load, during the test on the I-Ti and I-Cr samples, respectively. It
is concluded, based on force and AE signal and optical images, that coating delamination
initiated around 1.0 N for I-Ti and 3.5 N for I-Cr.
Figure 15 displays the SEM images at two load locations on the two samples, one is
around the coating delamination, another is at the end of scratch test with 5 N, and same results
with coating spallation along the scratch formed after coating delamination during scratch tests,
and more severe coating detachment were observed on the sample of I-Ti than I-Cr.
The results show that the critical load is only 1 N for the I-Ti, and 3.5N for I-Cr. Thus,
both are not effective with the current approach. The sample of I-Ti has the poorest adhesion
comparing to the samples discussed in this research. Cr-interlayer provides a slightly better
adhesion than Ti-interlayer. The possible reason is that the carbon diffusion in Cr is relatively
low compared to Ti, which should improve the adhesion of diamond to the seeded substrate.
However, the adhesion is still poorer than the diamond coating samples without interface in our
research. This is possible due to a defective chromium carbide layer formed during deposition. It
is known that the multi-phase system could provide an easy path for the micro-cracks due to

10.
10
transformation among these phases [21]. In addition, the mismatch of the coefficients of thermal
expansion in the multilayer structure aggregates the propagation of micro-cracks in the scratch
test.
Conclusions
Scratch testing of a diamond thin film deposited on a WC substrate has been carried out
using a micro-scratch tester. The objective is to evaluate the coating thickness and interlayer
effects on the coating delamination critical load. During the scratch tests, the normal force, the
tangential force, the acoustic emission signals and the penetration depth were acquired to identify
the delamination initiation event. After scratch tests, the scratch marks were also observed in a
digital microscope and a scanning electron microscope. The results are summarized as the
following.
(1) Coating delamination can be clearly detected by AE signals. It was observed that the abrupt
AE peak jumps followed by several continuous AE high-amplitude peaks are associated with
coating delamination. The tangential force increases smoothly with the normal force before
the initiation of coating delamination, but, varies considerably once coating delamination
initiated. Therefore, tangential force may also be used to monitor the coating delamination
during scratch tests.
(2) The width of coating delamination would increase with the increased loads after
delamination initiated, this is confirmed by the scratch images under digital microscope,
which show that the coating delamination becomes more severe with the increased load.
(3) The adhesion of the diamond coating increases with the increased coating thickness in the
range discussed. On the other hand,, the Ti-interlayer and Cr-interlayer do not seem to be
effective in interface adhesion enhancement compared to other conventional samples.
Acknowledgements
This research is supported by NSF, CMMI 0928627 - GOALI/Collaborative Research:
Interface Engineered Diamond Coatings for Dry Machining, between The University of Alabama,
General Motors and University of South Florida. The diamond-coated samples were provided by
the University of South Florida.

11.
11
References
[1] J. Hu, Y.K. Chou, R.G. Thompson, Trans. NAMRI/SME 35 (2007) 177.
[2] P. Lu, Y.K. Chou, R.G. Thompson. Proc. 2009 Int. Manuf. Sci. and Eng. Conf., (2009)
MSEC2009-84372.
[3] F. Qin, J. Hu, Y.K. Chou, R.G. Thompson. Wear 267 (2009) 991.
[4] Riccardo Polini, Massimiliano Barletta, Diamond and Related Materials, 2008, 17(3), 325-
335.
[5] Riccardo Polini, Fabio Pighetti Mantini, Massimiliano Barletta, Roberta Valle, Fabrizio
Casadei, Diamond and Related Materials, 2006, 15(9),1284-1291.
[6] Zhenqing Xu, Leonid Lev, Michael Lukitsch, Ashok Kumar, Diamond and Related Materials,
2007, 16(3), 461-466.
[7] J. Oakes, X.X. Pan, R. Haubner and B. Lux. Surf. Coat. Technol., 47 (1991), p. 600.
[8] E. Cappelli, F. Pinzari, P. Ascarelli and G. Righini. Diam. Relat. Mater., 5 (1996), p. 292.
[9] F. Deuerler, H. van den Berg, R. Tabersky, A. Freundlieb, M. Pies, V. Buck. Diamond and
Related Materials, Volume 5, Issue 12, December 1996, Pages 1478-1489.
[10] Humberto Gomez, Delcie Durham, Xingcheng Xiao, Michael Lukitsch, Ping Lu, Kevin
Chou, Anil Sachdev, Ashok Kumar, Journal of Materials Processing Technology, Volume 212,
Issue 2, February 2012, Pages 523-533.
[11] J.G. Buijnsters, P. Shankar, W. Fleischer, W.J.P. van Enckevort, J.J. Schermer, J.J. ter
Meulen, Diamond and Related Materials, Volume 11, Issues 3-6, March-June 2002, Pages 536-
544.
[12] F.J.G Silva, A.P.M Baptista, E Pereira, V Teixeira, Q.H Fan, A.J.S Fernandes, F.M Cost,
Diamond and Related Materials, Volume 11, Issue 9, September 2002, Pages 1617-1622.
[13] A.J. Perry. Thin Solid Films 107 (1983) 167.
[14] S.J. Bull in: W. Gissler, H.A. Jehn (Eds.), ECSC, EEC, EAEC, (1992) 31.
[15] H. Ollendorf, D. Schneider. Surf. Coat. Technol. 113 (1999) 86.
[16] R. Jaworski, L. Pawlowski, F. Roudet, S. Kozerski, F. Petit, Surf. Coat. Technol. 202 (2008)
2644.

12.
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[17] S. Nakao, J. Kim, J. Choi, S. Miyagawa, Y. Miyagawa, M. Ikeyama, Surf. Coat. Technol.
201 (2007) 8334.
[18] P. Lu, X. Xiao, M. Lukitsch, A. Sachdev, Y.K. Chou, Surface and Coatings Technology,
2011,206(7):1860-1866.
[19] A.J. Perry. Scratch adhesion testing of hard coatings, Thin Solid Films, Volume 107, Issue 2,
16 September 1983, Pages 167-180.
[20] X. Xiao, B.W. Sheldon, E. Konca, L.C. Lev, M.J. Lukitsch. Diamond and Related Materials,
2009, 18(9), Pages 1114-1117.
[21] Huang, B., M. Zhao and T. Zhang, 2004. Phil. Mag. Vol. 84, 1233-1256.

13.
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Table 1 Conditions of the pretreatments of the substrate
Denomination Pretreatment Conditions
T Chemical Etching 1. Acetone cleaning
2. K3(Fe(CN)6) + KOH + H2O
3. HNO3 + H2O2
4. DIW Rinse
I-Cr PVD Interlayer Cr/CrN/Cr [200nm/1.5um/1.5um]
I-Ti PVD Interlayer Ti/TiN/Ti [200nm/1.5um/1.5um]
Table 2 Sample details for diamond coated inserts in scratch tests
Denomination Interlayer Coating thickness/µm Surface roughness Ra/µm
T-1.5 N/A 1.5 4.45
T-2.5 N/A 2.5 3.82
T-4.5 N/A 4.5 2.76
I-Ti Ti 2 3.82
I-Cr Cr 4 2.23

14.
14
List of figures
Figure 1. Surface characteristics of the WC-Co (6%) surface as received from supplier, a) SEM
image of surface morphology representing the finishing marks on the tool and b)
optical interferometry image of the surface representing the roughness value and
pattern.
Figure 2. Raman spectra corresponding to the structure of the CVD films depicting the
microcrystalline diamond structure represented by the 1332 cm-1 broad peak.
Figure 3. SEM image corresponding to the diamond film deposited in the samples depicting the
faceted diamond polycrystals.
Figure 4. Digital microscopic images of scratch grooves on sample T-1.5.
Figure 5. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a maximum
load of 10 N.
Figure 6. Spot for a) load around 8N and b) end of scratch on scratch trace for max load of 10N
under microscope(X1000).
Figure 7. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a maximum
load of 20 N.
Figure 8. The digital microscopic images of a) Spot 1 around 9N, b) spot 2 around 13 N, and c)
the end of the scratch for scratch test under maximum load of 20 N.
Figure 9. The SEM image for the coating delamination on sample T-1.5 (20 N load) at a) 200X b)
800X.
Figure 10. Figure 12. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a
maximum load of 20 N, sample T-4.5.
Figure 11. The digital microscopic images of a) Spot 1 around 14.6 N, and b) the end of the
scratch for scratch test on sample T-4.5 under maximum load of 20 N.
Figure 12. SEM images at the scratch end location (20 N): a) T-1.5, b) T-2.5, and c) T-4.5.
Figure 13. Critical load for coating delamination vs. coating thickness.
Figure 14. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a maximum
load of 5 N on a) I-Ti and b) I-Cr.
Figure. 15. SEM images at the scratch end location (5 N): a) I-Cr, and b) I-Ti.

15.
Figure
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16.
16
Figure 4. Digital microscopic images of scratch grooves on sample T-1.5.
Figure 5. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a
maximumload of 10 N.
a)Spot around 8N b) End of scratch
Figure 6. Spot for a) load around 8N and b) end of scratch on scratch trace for max load of 10N
under microscope(X1000).
10N
30N
20N
Spot 1
#1
.
.
.
#8
0
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0
2
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8
0 2000 4000 6000 8000 10000
Tangential Force(mN)
Acoustic Emission(%)
Normal Force(mN)
AE Ft

17.
17
Figure 7. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a maximum
load of 20 N.
a)Spot 1 b) Spot 2 c) End of scratch
Figure 8. The digital microscopic images of a) Spot 1 around 9N, b) spot 2 around 13 N, and c)
the end of the scratch for scratch test under maximum load of 20 N.
a) 200X b) 800X
Figure 9. The SEM image for the coating delamination on sample T-1.5 (20 N load) at a) 200X b)
800X.
Spot 2
Spot 1
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2
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6
8
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14
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TangentialForce(mN)
AcousticEmission(%)
Normal Force(mN)
AE Ft

18.
18
Figure 10. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a maximum
load of 20 N, sample T-4.5.
(a)Spot 1 around 14.6N (b) End of scratch
Figure 11. The digital microscopic images of (a) Spot 1 around 14.6 N, and (b) the end of the
scratch for scratch test on sample T-4.5 under maximum load of 20 N.
Spot 1
0
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10000
0
2
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6
8
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14
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TangentialForce(mN)
AcousticEmission(%)
Normal Force(mN)
AE Ft

19.
19
Figure. 12. SEM images at the scratch end location (20 N): a) T-1.5, b) T-2.5, and c) T-4.5.
Figure 13. Critical load for coating delamination vs. coating thickness.
a) T-1.5 b) T-2.5
c) T-4.5
8
10
12
14
16
0 1 2 3 4 5
Criticalload(N)
Coating thickness(μm)

20.
20
a)I-Ti
b) I-Cr
Figure 14. Acoustic emission (AE) and tangential force (Ft) vs. normal load (Fn) for a maximum
load of 5 N on a) I-Ti and b) I-Cr.
Figure. 15. SEM images at the scratch end location (5 N): a) I-Cr, and b) I-Ti.
Spot 1
Spot 1
a) I-Cr b) I-Ti
0
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1500
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AcousticEmission(%)
Normal Force(mN)
AE Ft
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TangentialForce(mN)
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Normal Force(mN)
AE Ft