Tribological performance of TiN coatings deposited ...

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Wear 342-343 (2015) 77–84

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Tribological performance of TiN coatings deposited on 304 L stainless steel used for olive-oil extraction Amir Bahri a, Noamen Guermazi a,n,1, Khaled Elleuch a, Mustafa Ürgen b,2 a b

Laboratory of Materials Engineering and Environnement (LGME), National Engineering School of Sfax, University of Sfax, B.P.W.1173, 3038 Sfax, Tunisia Istanbul Technical University, Department of Metallurgical and Materials Engineering, 34469 Maslak, Istanbul, Turkey

art ic l e i nf o

a b s t r a c t

Article history: Received 7 May 2015 Received in revised form 30 July 2015 Accepted 14 August 2015 Available online 24 August 2015

Titanium-nitride (TiN) coatings have been developed and used by industry in numerous tribological applications, including machining, manufacturing and transportation. However, they have not attracted any attention as a tribological coating to be used in olive-oil extraction devices. In fact, since the separation of vegetation water and solid phase of the olive is always made in a continuous process and in very short time, the wear damage of the metallic devices used in this process is still a serious problem. The purpose of this study is to investigate the mechanical and tribological behaviors of TiN coating under a wide range of deposition conditions. The results of this study have confirmed that the coatings deposited using direct current (DC) bias present several distinct changes compared to those produced with pulse bias, depending on the magnitude of the duty cycle applied with and without Argon gas. Besides, different grain orientations have been detected for both kinds of TiN coatings. Tribological performances for the obtained TiN coatings were investigated using different configurations namely reciprocating sliding and pin-on-disk tests. The responses of these coatings in terms of friction coefficient and wear depth were discussed. The main results when sliding against olive seed and alumina ball as counterbody have clearly revealed a significant improvement of tribological properties with the application of DC and pulse bias voltage. Moreover, the tribological behavior of TiN did not change much with the addition of Ar gas. & 2015 Elsevier B.V. All rights reserved.

Keywords: Olive-oil extraction TiN coatings Stainless steel Wear Friction

1. Introduction Technology for olive-oil extraction has progressed significantly since the beginning of the nineties, when the mechanical procedures started to be used. By means of this technology, the oil, vegetation water and solid phase of the olive can be separated in a continuous process and very short time (Fig. 1). Unfortunately, the main disadvantage of this procedure is the damage of components that are in direct contact with the olive pomace by abrasive and erosive wear and corrosion, especially the crusher and the decanter (Fig. 1). Actually, these devices provide the rotation of the pomace (grignon) with a cylindrical hopper, which ensures the crushing and separation of the pit from the pulp. During the process of separation, a serious wear problem occurs which may lead to almost complete wearing of the scrapers in a very limited n

Corresponding author. E-mail address: [email protected] (N. Guermazi). 1 Tel.: þ216 74 274 088; fax: þ 216 74 275 595. 2 Tel.: þ90 2122856999; fax: þ 90 2122853427.

http://dx.doi.org/10.1016/j.wear.2015.08.012 0043-1648/& 2015 Elsevier B.V. All rights reserved.

duration of three weeks. In a recent study in the same context, it was shown that the potential damage results partially from an abrasive wear phenomenon [1]. In addition, following an expertize conducted on the damaged components, in particular in the crusher, we considered that there is partially an abrasive wear, as can be seen in Fig. 2. Practically, almost all of these components are made from stainless steel 304 L. In order to protect the stainless steel from wear damages, Physical Vapor Deposition (PVD) is one of the most common methods to improve the performance of stainless steel [2,3], reducing the wear under heavy loads and high temperatures. In fact, cathodic arc evaporation (CAE) is an attractive PVD technique both for its unique abilities (high deposition rates, highly ionized vapor, which allow ion energy control through substrate bias voltage, excellent adhesion), and its widely use in the coating industry [4–9]. Several coatings could be applied using techniques such as Molybdenum Nitride (MoN), Tungsten Carbide (WC) and Titanium Nitride (TiN). The most common used coating is TiN which has high hardness, good wear and good corrosion resistance and has been used as wear resistant coating for cutting tools and dies. In recent years, it started to be used on machine parts like

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Elevator

Centrifugal Purifier

Wear damage

Water Crusher

Water

Olives

Storage tank

Decanter

Oil

Mixer

Cleaning

Grignon

Impurities

Fig. 1. Olive-oil extraction process.

Wear

Wear

Fig. 2. Wear phenomena in the crusher.

automobile parts and they are assumed to be widely applied in industries [10–13]. Therefore, it may be considered as a good coating material to improve wear resistance as well as corrosion properties. However, it should be noted that, to the authors' knowledge, up to now the principal deposition parameters like direct-current (DC) bias voltage, pulse bias and Ar gas as well as their impact on tribological properties have not been clearly explained. In 2003, Kelly and co-workers [14] have reported that midfrequency (20–350 kHz) pulsed processing has an edge over continuous DC processing. In particular, they have shown that TiO2 and TiN films deposited at 20 kHz target frequency exhibited better optical and tribological properties than those deposited by continuous DC sputtering. It has equally been shown that adhesion, wear resistance and friction coefficient have been improved for coatings deposited using pulse bias when compared to those

applied with DC bias voltage. Recently, Hanizam and co-workers [15] have done a comparison between WC coatings produced using DC and some others obtained by pulse bias. They have shown a homogenous surface with finer and more globular microstructure of WC coating when using pulse bias voltage. However, the impact of the pulsed bias compared to DC on the tribological properties was not considered in this work. In a similar research work conducted by Bhaduri et al. [16], it was found that TiN structure becomes finer with the increase in bias frequency. Furthermore, the adhesion strength was found to increase until 200 kHz and then slightly decreases beyond this value. In the same context, Grun [17] reported in his study that a good adhesion for coatings could be obtained when using pulse bias. Ali et al. [18] studied the effects of substrate bias; temperature, nitrogen flow rate, and metal ion etching in surface roughness mainly depend on the conditions of sample preparation, surface treatment and other

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parameters. Akkaya et al. [19] have shown in their study the effects of pulse bias in structure and mechanical properties of TiN coatings, that (i) the crystal prefers orientation changing from (111) to (220) accompanied by structural transition and (ii) there is significant improvement of tribological properties with the application of pulse bias. Yongqiang et al. [20] have investigated the effects of pulsed bias ratio on the microstructure and surface properties of TiN coating. Among others, they have found that coatings deposited at 60% present the best hardness of 1160 HV and those coated with 40% duty ratio display the best resistance to corrosion. The effects of the process parameters such as temperature, pressure, gas ratios and flow rate on layer deposition behaviors have been reported in the literature [21,22]. Nevertheless, it is still challenging to establish a relationship between the deposition conditions, such as a duty cycle, Argon gas (Ar), and the properties of the deposited coatings. In the present work, different TiN coatings were deposited on stainless steel 304 L with cathodic arc evaporation (CAE) under several conditions. Indeed, these coatings were characterized and compared. A focus was made on their mechanical and tribological properties for reducing the abrasive wear damages largely produced in olive-oil extraction process.

2. Experimental studies In this study, all TiN coatings were deposited by cathodic arc evaporation (CAE) technique using a vacuum chamber with 70 cm in diameter and 70 cm in height (Fig. 3). A water-cooled metallic Ticathode with a diameter of 6 cm was used. Samples of stainless steel 304 L with dimensions of 30  30  2 mm3 were used as substrates for the deposition of TiN coatings. Before introducing into the vacuum chamber, these samples were firstly polished and then cleaned with acetone and propanol in an ultrasonic bath for 15 min. Some of the coatings were deposited under Argon gas (Ar) atmosphere in order to study the effect of introducing Ar on the performance of the resulted coatings. During the coating process for all samples, coating pressure was kept at 1 Pa (E7.5 10  3 Torr). However, the different substrate temperatures recorded (not imposed) during the coating deposition process are given in Table 1. A universal indenter (Fisher hardness tester) was used to evaluate the Vickers Hardness and Young's modulus of the studied samples from loading–unloading curves. Twenty individual

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measurements were taken under a load of 20 mN. The values were averaged to a mean data set. XRD characterization was performed using a Phillips PW 3710 mpd control X-ray diffraction system. Cu-Kα radiation was used in all investigations. For the investigation of orientation dependence of the coatings, XRD measurements were conducted in θ–2θ configuration. The grain size (coherent scattering zone) in the nitride films (D) was estimated from the (111), (200), (220), (311) and (222) peak broadening, using the Scherrer relation as follows:

D=

0.9 λ B cos θ

(1)

where B is the corrected full-width at half-maximum (FWHM) of a Bragg peak, λ is the X-ray wavelength, and θ is the Bragg angle [23]. The morphology and chemical composition of the coatings were determined by scanning electron microscope (SEM, Jeol JSM5410) and energy dispersive X-ray spectroscopy (EDS) techniques, Fig. 4. Meanwhile, the deposition rate can be obtained by dividing the thickness with deposition time. The surface roughness of uncoated and coated samples was measured using a surface roughness tester (Surtronic 25-Taylor Hobson). The tribological behavior of the coatings was carried out by the use of a pin-on-disk tribometer under dry conditions. The schematic illustration of the wear test apparatus is shown in Fig. 5. Two configurations were retained: reciprocating and rotating tests. One possible engineering reason for selecting the two sets of test conditions is to simulate the possible wear which can really be produced in the olive-oil extraction process (particularly in the decanter). We expect that the wear damage can be essentially the consequence of rotating or reciprocating the movement of the olive seed against the material of the decanter. It is to be noted that for each rotating experiment, a new olive seed was used, which can be considered as the originality for this experimental

Table 1 Temperatures for TiN coatings deposited at various duty cycles. Sample condition DC  150 V Pulse 1000 V-Duty Pulse 1000 V-Duty Pulse 1000 V-Duty Pulse 1000 V-Duty Pulse 1000 V-Duty Pulse 1000 V-Duty

Temperature (°C)

cycle cycle cycle cycle cycle cycle

14% 14% þ Ar 20% 20% þAr 25% 25% þAr

640 540 565 639 688 770 728

Pumping Vacuum chamber

Sample

Holder Cathode Bracket

Fig. 3. The used cathodic arc evaporation system.

Fig. 4. EDS analysis of the deposited TiN coating (case of the TiN sample produced with DC bias voltage).

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work. The testing parameters for both reciprocating and rotating tests are listed in Table 2. For a good repeatability of the results, all tests were triplicated and averages were considered. At the end of the experiment, the depth and width of the wear tracks were measured using 3D (WYKO NT1100) profilometer.

Controlled Load

Mounting Block Friction/Load Sensor Ball holder

Drive Motor

Alumina Ball Flat sample

3. Results and discussion 3.1. X-ray diffraction studies and grain size evolution XRD peaks of TiN coatings deposited on the 304 L stainless steel substrate in Ar þN2 and pure N2 atmospheres using different duty cycles are shown in Fig. 6. As can be seen from Fig. 6(a), the coating deposited in Arþ N2 using DC 150 V bias voltage exhibits (111) preferred orientation mixed with less (222) orientation. The same result was equally found by Akkaya et al. [19] in their study about the structure and properties of TiN coatings. However, those deposited using pulse bias voltage exhibit (111), (200), (220), (311) and (222) orientations for 14% duty cycle without Ar. There are mixed (111) and (220) preferred orientation with more pronounced (111) orientation. This changes when 20% of duty cycles is used, (220) preferred orientation becomes more important but still less than (111) orientation. Using 25% of duty cycle, (220) preferred orientation becomes high compared to (111) and (222) peak. There is also (200) peak which is more pronounced for 20% and 25% duty cycle compared with 14%. Concerning the substrates with the same variation of duty cycle with Ar gas introduced in the atmosphere (Fig. 6(b)), (220) preferred orientation is more pronounced than

Reciprocating slider DC 150 V

Controlled Load

Intensity

Pulse Duty cycle 14%

Pulse Duty cycle 20%

Mounting Block Pulse Duty cycle 25%

Friction/Load Sensor

Pin holder

2 θ (degree)

Pin in Olive seed Flat sample

Disc

Motor DC 150 V

Fig. 5. Configurations used for sliding experiments: (a) reciprocating wear test and (b) rotating wear tests.

Intensity

Pulse Duty cycle 14%+Ar

Pulse Duty cycle 20%+Ar

Table 2 Operating conditions of sliding experiments.

Normal load Counter body Velocity Relative humidity (RH) Test duration Temperature

Reciprocating sliding test

Rotating sliding test

From 1 to 10 N Alumina ball 0.01 m/s 40 7 3 25 min 287 2 °C

10 N Olive seed 0.31 m/s 407 3 90 min 287 2 °C

Pulse Duty cycle 25%+Ar

2 θ (degree) Fig. 6. Duty cycle dependent XRD patterns of PVD TiN coatings deposited on 304 L substrate: (a) without Ar and (b) with Ar.

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(111) and the other directions. However (311) peak is more important compared to the samples coated without Ar. In particular, a minor peak at 51° was observed, indicating (102) orientation [9], essentially in the case of coatings applied with Ar gas. It is well known that the orientations of crystals in TiN thin coatings are influenced by the variation of the duty cycle used in the pulse bias voltage which can have direct effect in the tribological properties. These findings are similar to the results obtained by Yongqiang and Chunzhi [24] in their study on the effect of pulse bias duty ratio on microstructure and the crystallite orientation. This study has found a difference between the wear resistances when changing the duty cycle. From the XRD peaks, the crystallite size in the TiN coatings was found to be between 20 nm and 23 nm in N2 atmosphere and between 13 nm and 20 nm in N2 þAr atmosphere, respectively (Fig. 7). It is observed from Fig. 7 that the grain size increases with the increase in the duty cycle until 20% and then it tends to decrease. Until 20% of the duty cycle, the results are in good agreement with those obtained by Raoufi et al. [25], who reported that the grain size increases as the duty cycle increases. However, after 20% of duty cycle, it can be observed that the grain size decreases for both TiN coatings applied with and without Ar gas. Similar result has been reported by Nishat et al. [26] when studying the effect of increasing the flow rate of the Ar gas on the grain size evolution. These authors have found that as the flow rate increases, the grain size of TiN coating increases. Besides, they have proven that the deposition of coatings under Ar gas and flow rate equal to 10 sccm give small grain size. In our work, a flow rate of 10 sccm was used, and the obtained grain size is similar to that found by Nishat and co-workers [26]. Therefore, the decreased grain size obtained for coatings processed in N2 þAr atmosphere could be probably attributed to the effect of the flow rate parameter.

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3.2. Mechanical performances analysis For the produced TiN coatings, thickness, hardness, elastic modulus and grain size were measured, then summarized in Table 3. As can be seen from Table 3, the thicknesses of the coatings were found between 6 and 10 μm. Consequently, the mean value of the deposition rate was about 16 μm/h. The resulting hardness values of the TiN coatings deposited at a temperature between 540 °C and 770 °C with and without Ar using various duty cycles are illustrated in Fig. 8. The hardness values varied from the duty cycle 14% with a hardness of 24.87 GPa to the duty cycle of 25% with a hardness of 34.83 GPa for the sample coated without Ar. Regarding the sample coated with Ar, the hardness varied from 29.44 to 33.55 GPa for 14% and 20% of duty cycle, respectively. Thus, the hardness of the TiN coatings increased with the increase in the duty cycle, which can be ascribed to the evolution of the grain size. Actually, there was a little increase until a 20% of duty cycle after that it started to decrease. Reducing the grain size was found to improve the hardness of TiN coatings. The obtained results are in good accordance with those reported in the research work of Park et al. [27]. The most commonly used parameter for characterizing the roughness of PVD coatings in industry is the roughness average (Ra) [28,29]. For this reason, the variation in the surface roughness for both uncoated and coated samples was studied. The surface roughness was measured at five different locations and the average value was considered. The results are summarized in Table 4. It is to be noted from Table 4 that the surface roughness is around 0.12 μm for the uncoated sample, while it is about 0.38 μm for the sample coated with DC 150 V. For the sample coated with pulse bias with different duty cycles, it is between 0.26 and 0.38 μm. It can be seen from the data that the roughness for the coated sample is significantly higher than in the case of the uncoated one. This can be explained by the presence of macro-

Fig. 8. Hardness evolution of TiN coatings for various duty cycles.

Fig. 7. The grain size evolution of TiN coatings for various duty cycles.

Table 3 Thickness and elastic modulus of TiN coatings deposited at various duty cycles. Sample DC  150 V Pulse 1000 V-Duty Pulse 1000 V-Duty Pulse 1000 V-Duty Pulse 1000 V-Duty Pulse 1000 V-Duty Pulse 1000 V-Duty

cycle cycle cycle cycle cycle cycle

14% 14% þAr 20% 20% þ Ar 25% 25% þ Ar

Table 4 Surface roughness of substrate and TiN coatings. Duty cycles (%)

Samples Substrate

DC 150 (V)

Thickness (μm)

Elastic modulus (GPa)

Ra (μm)

Rz (μm) Rq (μm) Ra (μm)

Rz (μm) Rq (μm)

8.97 71.5 6.3371.2 7.97 71.4 10.30 71.8 7.60 71.3 8.00 71.6 7.20 71.2

341.42 7 17.4 278.56 7 15.5 273.60 7 14.7 276.34 7 15.3 303.45 7 16.2 338.64 7 16.8 315.92 7 16.6

0.12

1.18

14 20 25

Coated without Ar 0.38 0.35 0.26

3.39 3.36 2.80

0.17

0.38

3.06

0.48

0.49 0.48 0.36

Coated with Ar 0.33 0.31 0.38

3.32 3.33 4.16

0.45 0.42 0.55

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droplets and pitting defects which generally lead to the increase in the roughness of TiN coatings (Fig. 9). In addition, it seems to have a significant influence on the performance of the coatings, particularly in terms of wear resistance [30]. From Fig. 9(a), the presence of some droplets for the coating applied with DC bias voltage can be observed, but still low comparing to the other coatings. This indicates that DC coating is more uniform, compact, dense with smaller and fewer droplets when compared to those elaborated at different duty cycles. Fig. 9 (b) and (c) shows the morphology of the coatings applied using 25% duty cycle without and with the presence of Ar gas. Besides, the effect of the duty cycle and Ar gas on the increase of the density of the droplets can be clearly seen. This obviously proves the hardness and the higher Young's modulus for these DC coatings. 3.3. Tribological behavior 3.3.1. Rotating wear test 3.3.1.1. The friction coefficients. Friction coefficient behaviors for the TiN coatings applied with and without Ar gas are shown in Fig. 10. The evolution of friction coefficient was studied as a function of time during 90 min. For the coatings applied without Ar (Fig. 10 (a)), it has been shown that both TiN coatings coated with 14% and 25% of duty cycle display similar behavior. The friction coefficient reached directly a value of 0.12 and then remained constant during

the entire test. Similar results were found by Tannoa et al. [31] when focusing on the relation between the friction coefficient of the TiN coatings with crystallite orientation. However, for the coating coated with 25% duty cycle, the first part of the curve represents a rapid increase until approximately 0.9. Concerning the second part, it represents a typical relative steady state wear regime. The same phenomenon can be seen in Fig. 10(b) for the coatings applied using 14%, 20% and 25% duty cycle with Ar gas distinguished with obvious fluctuation in the first part of the curve. In the second part, the friction coefficient was stable for the three coatings and was between 0.82 and 0.95. Similar shape friction for four coatings can be related to the wear debris generated from the olive seed because it leads to a rapid increase in the friction coefficient. 3.3.1.2. Wear resistance. Fig. 11 shows the evolution of the wear depth as function of duty cycle for both coatings applied with DC bias and pulse bias voltage. It is worthy to note that the best wear resistance was observed for both coatings applied with DC 150 V and pulse bias 20% duty cycle. This can be explained by the fact that it is characterized by the lowest number of droplets that can affect the wear resistance as previously observed. For the TiN coatings coated without Ar, it can be seen that the best wear resistance was for the coating with 20% duty cycle. Nonetheless, for those coated using Ar gas, it was for 14% duty cycle. The addition of Ar into the hard coatings does not have a significant positive effect on the wear behavior of the

Fig. 9. SEM morphology of TiN coatings deposited with DC and pulse bias voltage: (a) DC  150 V; (b) duty cycle 25% and (c) duty cycle 25% þAr.

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make a comparison between the studied coatings. For this reason, in the following section reciprocating wear tests have been conducted using alumina ball in order to accelerate the wear rate evolution under different applied loads. The reason for choosing reciprocating wear test is that olive pomace translation movement presents the lowest percentage of displacement compared to the rotational movement. So, we choose the low conditions that can make wear in the olive-oil extraction devices.

1

Friction coefficient

0.8

0.6 TiN duty cycle 20% TiN DC -150 v Substrate TiN duty cycle 25% TiN duty cycle 14%

0.4

0.2

0

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

Time (s)

1

Friction coefficient

0.8

0.6

TiN duty cycle 25%+Ar TiN duty cycle 20%+Ar TiN duty cycle 14%+Ar TiN DC -150 v Substrate

0.4

0.2

0

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

83

5500

Time (s)

Fig. 10. Evolution of the friction coefficient of TiN coatings: (a) applied without Ar and (b) applied with Ar.

3.3.2. Reciprocating wear test The results of the reciprocating wear tests conducted by alumina ball against TiN coatings are presented in Fig. 12. The variation of the wear depth as a function of the normal load has revealed that the wear depth increases as the normal load increases. It can be seen that for all coatings, the maximum wear depth did not reach the substrate. Besides, the best wear resistance was observed for both coatings applied with DC  150 V and pulse bias 25% duty cycle without Ar. Therefore, we come to the conclusion that the wear resistance is better for the coating produced by DC bias than for the pulse bias. These findings are partially in good agreement with those reported in the literature [14] when comparing between titanium based film produced by pulsed and DC bias voltage. In such research works, it was found that coatings deposited by pulsed bias are characterized by good tribological properties compared to those performed with DC bias. In the present work, the coating applied using 25% duty cycle without Ar presents better wear resistance compared to that applied with DC  150 V. This can be explained by the fact that beyond a specific frequency, the tribological properties for pulse bias become better than those coated with DC bias. These two coatings could be good candidates to be used in olive-oil extraction process when the olive seeds are livened up in small reciprocating movements against the material of the decanter. On the other hand, when comparing coatings produced with and without Ar, it

Fig. 11. Wear depth as a function of duty cycle for the substrate and TiN coatings applied with DC bias and pulse bias voltage.

TiN coatings. In addition, there is no significant evolution of the wear resistance when increasing the duty cycles. These results are consistent with the finding of Aliofkhazraei et al. [32]. When comparing the wear depth of the substrate with the TiN coating applied with DC  150 V as well as with those applied with pulse bias voltage, a good contribution for the TiN coating applied in terms of wear resistance can be noticed. These results are similar with the findings of Cozza et al. [33] who have explained this fact by the effect of the high residual stress in the coatings applied with pulse bias voltage which can affect directly the wear behavior. As previously discussed, the wear tests using olive seed as counterbody have shown that the wear depth for the stainless steel could be easily quantified. Meanwhile, for the TiN coatings the wear damage was not significant. Thus, it will be difficult to

Fig. 12. Evolution of the wear depth as a function of applied load for the different TiN coatings.

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can be concluded that there is no significant contribution for the Ar for improving wear resistance. However, when analyzing the maximum wear depth as a function of duty cycle, it can be seen that an increase in duty cycle enhances the wear resistance for both coatings applied with and without Ar gas.

4. Conclusion In this study, TiN coating with DC and pulse bias voltage were produced by cathodic arc evaporation (CAE) technique to investigate the impact of the duty cycle on their mechanical and tribological behavior. The hardness, roughness, elastic modulus, thicknesses, crystallite orientation, friction coefficient and wear depth were measured with the help of nano-indentation, profilometer and pin-on-disk tribometer. It was found that the best hardness was for the coating applied with DC bias voltage. For the coatings applied using pulse bias without Ar, the hardness increases with the duty cycle. For those elaborated with Ar, the obtained hardness was between 29.44 and 33.55 GPa. The XRD measurements have clearly shown the effect of the duty cycle on the crystallite orientation which has an influence on the wear resistance of the TiN coatings. The best wear resistance was found for the coating elaborated using DC bias voltage and pulse bias 25% duty cycle. There is a good correlation between the reciprocating and the rotating wear test. Concerning those produced with pulse bias; wear resistance increases with the duty cycle for the coating without Ar. As for those elaborated with Ar, it was expected that the Ar gas would improve the wear resistance for the coating but there was no obvious influence. Finally, it can be concluded that whatever the experimental conditions, the TiN coatings applied with DC and pulse bias voltage without Ar when it reaches 25% duty cycle significantly improve the mechanical properties for stainless steel 304 L used as substrate. In a future research work, our attention will be focussed on the investigation of the tribocorrosion response for the TiN coatings in a mixed environment containing water and olive. In addition, a comparative study will be conducted between TiN and TiAlN.

Acknowledgments This work was partially supported by EU-FP7 grant Oil & Sugar (295202).

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