3.3.1. Frictional and wear properties under dry conditions

Figure 9 shows the variation of the coefficient of friction as a function of the number of sliding cycles for the investigated mono- and multilayer systems under dry conditions at room temperature. The coefficient of friction was taken as the average of four tests. Although the SiNx, TiAlNx, and TiAlN/SiNx coatings showed similar friction coefficients (1.11, 0.93, and 0.99, respectively) in frictional contact with a steel counterpart (Figure 9a-c), the abrasive wear of the SiNx and TiAlN coating was greater than that of the TiAlN/SiNx coating. Investigations of the wear after testing were performed with an optical microscope. Corresponding optical photomicrographs and cross-sectional images of the wear marks formed on the coatings are shown in Figure 10, comparing the monolayer SiNx, TiAlN, and multilayer TiAlN/SiNx films. The average cross-sectional areas of the wear tracks were measured at three or more locations after 30,000 revolutions. For the dry conditions, the wear depth of SiNx was over 29.5 μm (Figure 10a) and that of the TiAlN was approximately 13.6 μm (Figure 10b). The TiAlN/SiNx film had a wear depth of 9.9 μm (Figure 10c) and showed better wear resistance than that of the SiNx and TiAlN films. Although the TiAlN film showed lower friction coefficients than that of the TiAlN/SiNx film (Figure 9a–c), the abrasive wear of the TiAlN film was greater than that of the TiAlN/SiNx film. The wear resistance of the TiAlN/SiNx film was enhanced owing to its nanolayer microstructure and small grain size compared with that of the TiAlN film. We believe that the decrease of the grain diameter might have caused a decrease of the surface roughness, which led to the improved tribological properties of the coating. Conversely, as shown in Figure 9c-f, the monolayer TiAlN + CNx film showed a lower friction coefficient

multilayer TiAlN/CNx + CNx film, as shown in Figure 9f. Corresponding optical photomicrographs and cross-sectional images of the wear marks formed on the films are shown in Figures 11 and 12. The size of wear scar was calculated from the cross-sectional area of the central portion of the wear mark. The average cross-sectional areas of the wear tracks were obtained at three or more locations after 30,000 revolutions, and the size of wear scar of the

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Figure 11. Wear profiles of (a) TiAlN, (b) TiAlN + CNx, (c) TiAlN/CNx + TiAlN, and (d) TiAlN/CNx + CNx coatings after

Figure 12. Cross-sectional images of wear created by SRV testing under dry conditions on (a) TiAlN, (b) TiAlN + CNx, (c)

SRV testing under dry conditions.

TiAlN/CNx + TiAlN, and (d) TiAlN/CNx + CNx coatings.

Figure 9. Friction coefficient vs. number of sliding cycles for the SRV friction test under dry conditions for: (a) SiNx, (b) TiAlN, (c) TiAlN/SiN, (d) TiAlN/CNx + TiAlN, (e) TiAlN + CNx, and (f) TiAlN/CNx + CNx coatings.

Figure 10. Wear profiles of the SiNx (a), TiAlN (b) and TiAlN/SiNx (c) coatings after SRV testing under dry conditions.

(approximately 0.71, as shown in Figure 9e) followed by 0.93 for the monolayer TiAlN (Figure 9b), 0.99 for the TiAlN/SiNx (Figure 9c), and 1.03 for TiAlN/CNx + TiAlN (Figure 9d) films. Thus, the TiAlN film with the CNx top layer had the second lowest friction coefficient of approximately 0.71. Notably, the TiAlN/CNx films with the CNx top layer had considerably lower friction coefficients than the other coatings. Furthermore, the lowest friction coefficient (approximately 0.62), which also showed a tendency to further decrease, was observed for the multilayer TiAlN/CNx + CNx film, as shown in Figure 9f. Corresponding optical photomicrographs and cross-sectional images of the wear marks formed on the films are shown in Figures 11 and 12. The size of wear scar was calculated from the cross-sectional area of the central portion of the wear mark. The average cross-sectional areas of the wear tracks were obtained at three or more locations after 30,000 revolutions, and the size of wear scar of the

Figure 11. Wear profiles of (a) TiAlN, (b) TiAlN + CNx, (c) TiAlN/CNx + TiAlN, and (d) TiAlN/CNx + CNx coatings after SRV testing under dry conditions.

Figure 12. Cross-sectional images of wear created by SRV testing under dry conditions on (a) TiAlN, (b) TiAlN + CNx, (c) TiAlN/CNx + TiAlN, and (d) TiAlN/CNx + CNx coatings.

(approximately 0.71, as shown in Figure 9e) followed by 0.93 for the monolayer TiAlN (Figure 9b), 0.99 for the TiAlN/SiNx (Figure 9c), and 1.03 for TiAlN/CNx + TiAlN (Figure 9d) films. Thus, the TiAlN film with the CNx top layer had the second lowest friction coefficient of approximately 0.71. Notably, the TiAlN/CNx films with the CNx top layer had considerably lower friction coefficients than the other coatings. Furthermore, the lowest friction coefficient (approximately 0.62), which also showed a tendency to further decrease, was observed for the

Figure 10. Wear profiles of the SiNx (a), TiAlN (b) and TiAlN/SiNx (c) coatings after SRV testing under dry conditions.

Figure 9. Friction coefficient vs. number of sliding cycles for the SRV friction test under dry conditions for: (a) SiNx, (b)

TiAlN, (c) TiAlN/SiN, (d) TiAlN/CNx + TiAlN, (e) TiAlN + CNx, and (f) TiAlN/CNx + CNx coatings.

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films were recorded after testing. The size of wear scar of the TiAlN films was greater than 5645 μm<sup>2</sup> (Figures 11a and 12a), while that of the TiAlN/CNx + TiAlN film size was approximately 5347 μm2 (Figures 11c and 12c). However, the sizes of wear scar of the TiAlN + CNx and the TiAlN/CNx + CNx films were 1169 and 331 μm<sup>2</sup> , as shown in Figures 11b and d and 12b and d, respectively. The TiAlN/CNx + TiAlN film showed better wear resistance than the TiAlN film. The improvement in wear resistance can be attributed to the introduction of a large number of TiAlN/CNx interfaces and refinement of the multilayer microstructure. The friction coefficient and size of wear scar of the TiAlN + CNx and TiAlN/CNx + CNx films were small, such that the wear resistance values were clearly improved by the deposition of the CNx top layer because the CNx film has both wear resistance and lubricating properties [8–10].

the TiAlN and TiAlN/CNx + TiAlN films showed similar friction coefficients, the size of wear scar of the TiAlN film is larger than that of TiAlN/CNx + TiAlN, indicating that the wear resistance of the TiAlN/CNx + TiAlN film was improved by the multilayered structure. However, the wear resistance and friction coefficients of the TiAlN + CNx and TiAlN/CNx + CNx films were considerably improved owing to the deposition of CNx [7], which has both wear resistance and lubricating properties [8–10]. This result is consistent with the reduced surface roughness and grain diameters of the films. Notably, the lowest friction and wear depths under the water lubrication conditions were obtained for the coatings with the CNx top layer, indicating that the wear resistance of the CNx layer is higher in humid air. Specifically, the lowest friction coefficients were 0.23 and 0.22 for the TiAlN + CNx and TiAlN/CNx + CNx coatings,

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Figure 14. Wear profiles of the SiNx, TiAlN, and TiAlN/SiNx coatings after SRV testing under water lubrication.

Figure 15. Wear profiles of (a) TiAlN, (b) TiAlN/CNx + TiAlN, (c) TiAlN + CNx, and (d) TiAlN/CNx + CNx coatings after

SRV testing under water lubrication.

### 3.3.2. Frictional and wear properties under water lubrication

The friction coefficients of the coatings were measured in the sliding system with the use of water as a lubricant. As shown in Figure 13, the friction coefficients of the SiNx, TiAlN, TiAlN/ SiNx, TiAlN/CNx + TiAlN, TiAlN + CNx, and TiAlN/CNx + CNx films were 0.54, 0.46, 0.52, 0.45, 0.23, and 0.22 (Figure 13a-f, respectively). For the monolayer SiNx and TiAlN, and multilayer TiAlN/SiNx, as shown in Figure 14, although a large wear track (approximately 28.1 μm deep) was observed for the monolayer SiNx (Figure 14a), no apparent wear tracks were observed for the TiAlN (Figure 14b) and TiAlN/SiNx (Figure 14c) films under water lubrication. This result indicates that the wear resistance of the TiAlN and TiAlN/SiNx films was improved by water lubrication [4, 7].

For the TiAlN, TiAlN/CNx + TiAlN, TiAlN + CNx, and TiAlN/CNx + CNx samples, optical photographs and cross-sectional images of the wear tracks formed on the coatings are shown in Figures 15 and 16. The wear of the films was evaluated from the size of wear scar, as described earlier. We observed that the mean sizes of wear scar were 301, 296, 203, and 184 μm2 for the TiAlN, TiAlN/CNx + TiAlN, TiAlN + CNx, and TiAlN/CNx + CNx films, respectively. Although

Figure 13. Friction coefficients of the coatings determined by SRV testing under water lubrication.

the TiAlN and TiAlN/CNx + TiAlN films showed similar friction coefficients, the size of wear scar of the TiAlN film is larger than that of TiAlN/CNx + TiAlN, indicating that the wear resistance of the TiAlN/CNx + TiAlN film was improved by the multilayered structure. However, the wear resistance and friction coefficients of the TiAlN + CNx and TiAlN/CNx + CNx films were considerably improved owing to the deposition of CNx [7], which has both wear resistance and lubricating properties [8–10]. This result is consistent with the reduced surface roughness and grain diameters of the films. Notably, the lowest friction and wear depths under the water lubrication conditions were obtained for the coatings with the CNx top layer, indicating that the wear resistance of the CNx layer is higher in humid air. Specifically, the lowest friction coefficients were 0.23 and 0.22 for the TiAlN + CNx and TiAlN/CNx + CNx coatings,

films were recorded after testing. The size of wear scar of the TiAlN films was greater than 5645 μm<sup>2</sup> (Figures 11a and 12a), while that of the TiAlN/CNx + TiAlN film size was approximately 5347 μm2 (Figures 11c and 12c). However, the sizes of wear scar of the TiAlN + CNx

12b and d, respectively. The TiAlN/CNx + TiAlN film showed better wear resistance than the TiAlN film. The improvement in wear resistance can be attributed to the introduction of a large number of TiAlN/CNx interfaces and refinement of the multilayer microstructure. The friction coefficient and size of wear scar of the TiAlN + CNx and TiAlN/CNx + CNx films were small, such that the wear resistance values were clearly improved by the deposition of the CNx top

The friction coefficients of the coatings were measured in the sliding system with the use of water as a lubricant. As shown in Figure 13, the friction coefficients of the SiNx, TiAlN, TiAlN/ SiNx, TiAlN/CNx + TiAlN, TiAlN + CNx, and TiAlN/CNx + CNx films were 0.54, 0.46, 0.52, 0.45, 0.23, and 0.22 (Figure 13a-f, respectively). For the monolayer SiNx and TiAlN, and multilayer TiAlN/SiNx, as shown in Figure 14, although a large wear track (approximately 28.1 μm deep) was observed for the monolayer SiNx (Figure 14a), no apparent wear tracks were observed for the TiAlN (Figure 14b) and TiAlN/SiNx (Figure 14c) films under water lubrication. This result indicates that the wear resistance of the TiAlN and TiAlN/SiNx films

For the TiAlN, TiAlN/CNx + TiAlN, TiAlN + CNx, and TiAlN/CNx + CNx samples, optical photographs and cross-sectional images of the wear tracks formed on the coatings are shown in Figures 15 and 16. The wear of the films was evaluated from the size of wear scar, as described earlier. We observed that the mean sizes of wear scar were 301, 296, 203, and 184 μm2 for the TiAlN, TiAlN/CNx + TiAlN, TiAlN + CNx, and TiAlN/CNx + CNx films, respectively. Although

Figure 13. Friction coefficients of the coatings determined by SRV testing under water lubrication.

layer because the CNx film has both wear resistance and lubricating properties [8–10].

, as shown in Figures 11b and d and

and the TiAlN/CNx + CNx films were 1169 and 331 μm<sup>2</sup>

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3.3.2. Frictional and wear properties under water lubrication

was improved by water lubrication [4, 7].

Figure 14. Wear profiles of the SiNx, TiAlN, and TiAlN/SiNx coatings after SRV testing under water lubrication.

Figure 15. Wear profiles of (a) TiAlN, (b) TiAlN/CNx + TiAlN, (c) TiAlN + CNx, and (d) TiAlN/CNx + CNx coatings after SRV testing under water lubrication.

Figure 17. Average friction coefficients for monolayer and multilayer films under dry conditions and water and PAO

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Figure 18. Images and cross-sectional of wear created by SRV testing under PAO lubrication on (a) TiAlN, (b) TiAlN/

CNx + TiAlN, (c) TiAlN + CNx, and (d) TiAlN/CNx + CNx coatings.

lubrication.

Figure 16. Cross-sectional images of wear created by SRV testing under water lubrication on the (a) TiAlN, (b) TiAlN/ CNx + TiAlN, (c) TiAlN + CNx, and (d) TiAlN/CNx + CNx coatings.

values which were, respectively, 49 and 51% of the friction coefficient for the coatings without the CNx layer [7].

#### 3.3.3. Frictional and wear properties under PAO lubrication

Figure 17 shows the variation of the coefficient of friction measured from SRV testing under PAO lubrication. The mean values of the friction coefficients for SiNx, TiAlN, TiAlN/SiNx, TiAlN/CNx + TiAlN, TiAlN + CNx, and TiAlN/CNx + CNx coatings were 0.18, 0.16, 0.19, 0.15, 0.15, and 0.14 (Figure 17a-f, respectively). Although the differences among the friction coefficients of the coatings was small, the TiAlN and TiAlN/CNx + TiAlN films with the CNx top layer had lower friction coefficients than those without the CNx top layer. The wear tracks formed on the coatings were observed by laser microscopy. Optical photographs and crosssectional images of the wear tracks are shown in Figure 18. The size of wear scar was markedly reduced for all coatings measured by SRV testing under PAO lubrication compared with those under dry and water conditions. The sizes of wear scar were 73.0, 24.0, 14.7, and 14.3 μm2 for the TiAlN, TiAlN + CNx, TiAlN/CNx + TiAlN, and TiAlN/CNx + CNx films. The PAO lubricant reduced the size of wear scar for the coatings with and without the CNx top layer. For the multilayer TiAlN/CNx + TiAlN, the size of wear scar of the TiAlN/CNx + TiAlN film was lower and similar to that of the TiAlN/CNx + CNx film when PAO was introduced as a Surface Morphology and Tribological Properties of Nanoscale (Ti, Al, Si, C)N Multilayer Coatings Deposited by… http://dx.doi.org/10.5772/intechopen.73141 93

Figure 17. Average friction coefficients for monolayer and multilayer films under dry conditions and water and PAO lubrication.

values which were, respectively, 49 and 51% of the friction coefficient for the coatings without the

Figure 16. Cross-sectional images of wear created by SRV testing under water lubrication on the (a) TiAlN, (b) TiAlN/

Figure 17 shows the variation of the coefficient of friction measured from SRV testing under PAO lubrication. The mean values of the friction coefficients for SiNx, TiAlN, TiAlN/SiNx, TiAlN/CNx + TiAlN, TiAlN + CNx, and TiAlN/CNx + CNx coatings were 0.18, 0.16, 0.19, 0.15, 0.15, and 0.14 (Figure 17a-f, respectively). Although the differences among the friction coefficients of the coatings was small, the TiAlN and TiAlN/CNx + TiAlN films with the CNx top layer had lower friction coefficients than those without the CNx top layer. The wear tracks formed on the coatings were observed by laser microscopy. Optical photographs and crosssectional images of the wear tracks are shown in Figure 18. The size of wear scar was markedly reduced for all coatings measured by SRV testing under PAO lubrication compared with those under dry and water conditions. The sizes of wear scar were 73.0, 24.0, 14.7, and 14.3 μm2 for the TiAlN, TiAlN + CNx, TiAlN/CNx + TiAlN, and TiAlN/CNx + CNx films. The PAO lubricant reduced the size of wear scar for the coatings with and without the CNx top layer. For the multilayer TiAlN/CNx + TiAlN, the size of wear scar of the TiAlN/CNx + TiAlN film was lower and similar to that of the TiAlN/CNx + CNx film when PAO was introduced as a

3.3.3. Frictional and wear properties under PAO lubrication

CNx + TiAlN, (c) TiAlN + CNx, and (d) TiAlN/CNx + CNx coatings.

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CNx layer [7].

Figure 18. Images and cross-sectional of wear created by SRV testing under PAO lubrication on (a) TiAlN, (b) TiAlN/ CNx + TiAlN, (c) TiAlN + CNx, and (d) TiAlN/CNx + CNx coatings.

lubricant. This result suggests that under these lubricant conditions a beneficial tribolayer forms on the wear surface, which provides a low coefficient of friction.

observed by laser microscopy. Figure 21 shows the profile and cross-section images of the wear tracks. The sizes of wear scar of the TiAlN (Figure 21a) and TiAlSiN (Figure 21b)

Surface Morphology and Tribological Properties of Nanoscale (Ti, Al, Si, C)N Multilayer Coatings Deposited by…

single layer TiAlN and multilayer layer TiAlSiN coatings. The wear resistance of the multilayer TiAlCrSiN coating was further improved by incorporation Cr into the TiAlSiN coating.

Friction properties and wear resistance to abrasive wear and oxidation are important characteristics for high-speed and cutting application. The lifetimes of the monolayer TiAlN, and multilayer TiAlSiN and TiAlCrSiN coated 6-mm diameter WC–Co drills (OSG Corporation, Japan) in wet (water soluble fluid) drilling of carbon steel (S50C, 50-53HRC) are shown in

. The multilayer TiAlCrSiN coating (Figure 21c)

) compared with that of the

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coatings were 1.6 105 and 7.9 104 <sup>μ</sup>m<sup>2</sup>

showed a lower size of wear scar (approximately 3.6 104 <sup>μ</sup>m<sup>2</sup>

Figure 20. Friction coefficients of the coatings by pin-on-disc testing under dry conditions.

Figure 21. Wear tracks and cross-sectional images of the coatings subjected to pin-on-disc test under dry conditions.

The friction coefficients of the films, as determined by SRV friction testing, are summarized in Figure 19 for dry, water, and PAO conditions. The coatings with the CNx top layer showed a lower friction coefficient under dry and water conditions than the coatings without the CNx top layer. However, all the coatings showed low friction coefficients owing to the introduction of water or PAO lubricants. This result suggests that lubricants such as water and PAO can improve the tribological properties in terms of friction and wear control in, for example, cutting applications.

#### 3.4. Performance of single layer and multilayer coatings in drilling

Single layer TiAlN, and nanoscale multilayer TiAlSiN and TiAlCrSiN coatings were prepared on cemented carbide pins and WC–Co drills by reactive magnetron sputtering deposition. The deposition conditions are detailed in previous reports [4, 7]. The tribological characteristics of the films were investigated with the use of a pin-on-disc friction test. The pin-on-disc wear test was performed at an air humidity of 50 10% and a temperature of 25 3C with a pin-ondisc tribometer featuring a counterpart composed of cemented carbide [4]. The wear test was performed at a load of 2 N and a linear speed of 150 mm/s for a total sliding time of 900 s (corresponding to a sliding distance of 135 m). Figure 20 compares the friction coefficients of the TiAlN, TiAlSiN, and TiAlCrSiN films. The TiAlCrSiN (Figure 20c) showed a stable and low friction coefficient in the range of 0.35–0.42; the values for TiAlN and TiAlSiN were 0.53 and 0.54, respectively (Figure 20a and b). The stable frictional properties of the TiAlCrSiN film were attributed to the nanolayer microstructure. The wear tracks formed on the films were

Figure 19. Average friction coefficients for monolayer and multilayer films under dry conditions and water and PAO lubrication.

observed by laser microscopy. Figure 21 shows the profile and cross-section images of the wear tracks. The sizes of wear scar of the TiAlN (Figure 21a) and TiAlSiN (Figure 21b) coatings were 1.6 105 and 7.9 104 <sup>μ</sup>m<sup>2</sup> . The multilayer TiAlCrSiN coating (Figure 21c) showed a lower size of wear scar (approximately 3.6 104 <sup>μ</sup>m<sup>2</sup> ) compared with that of the single layer TiAlN and multilayer layer TiAlSiN coatings. The wear resistance of the multilayer TiAlCrSiN coating was further improved by incorporation Cr into the TiAlSiN coating.

lubricant. This result suggests that under these lubricant conditions a beneficial tribolayer

The friction coefficients of the films, as determined by SRV friction testing, are summarized in Figure 19 for dry, water, and PAO conditions. The coatings with the CNx top layer showed a lower friction coefficient under dry and water conditions than the coatings without the CNx top layer. However, all the coatings showed low friction coefficients owing to the introduction of water or PAO lubricants. This result suggests that lubricants such as water and PAO can improve the tribological properties in terms of friction and wear control in, for example,

Single layer TiAlN, and nanoscale multilayer TiAlSiN and TiAlCrSiN coatings were prepared on cemented carbide pins and WC–Co drills by reactive magnetron sputtering deposition. The deposition conditions are detailed in previous reports [4, 7]. The tribological characteristics of the films were investigated with the use of a pin-on-disc friction test. The pin-on-disc wear test was performed at an air humidity of 50 10% and a temperature of 25 3C with a pin-ondisc tribometer featuring a counterpart composed of cemented carbide [4]. The wear test was performed at a load of 2 N and a linear speed of 150 mm/s for a total sliding time of 900 s (corresponding to a sliding distance of 135 m). Figure 20 compares the friction coefficients of the TiAlN, TiAlSiN, and TiAlCrSiN films. The TiAlCrSiN (Figure 20c) showed a stable and low friction coefficient in the range of 0.35–0.42; the values for TiAlN and TiAlSiN were 0.53 and 0.54, respectively (Figure 20a and b). The stable frictional properties of the TiAlCrSiN film were attributed to the nanolayer microstructure. The wear tracks formed on the films were

Figure 19. Average friction coefficients for monolayer and multilayer films under dry conditions and water and PAO

forms on the wear surface, which provides a low coefficient of friction.

3.4. Performance of single layer and multilayer coatings in drilling

cutting applications.

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lubrication.

Friction properties and wear resistance to abrasive wear and oxidation are important characteristics for high-speed and cutting application. The lifetimes of the monolayer TiAlN, and multilayer TiAlSiN and TiAlCrSiN coated 6-mm diameter WC–Co drills (OSG Corporation, Japan) in wet (water soluble fluid) drilling of carbon steel (S50C, 50-53HRC) are shown in

Figure 20. Friction coefficients of the coatings by pin-on-disc testing under dry conditions.

Figure 21. Wear tracks and cross-sectional images of the coatings subjected to pin-on-disc test under dry conditions.

Figure 22. The performances of the multilayer TiAlSiN and TiAlCrSiN coatings were compared with that of the single layer TiAlN coating, which was used as reference. The drilling tests were performed on a drill-milling machine NH4000 (DMG MORI, Japan) at a cutting speed of 100 m/min (5304 rpm), feed rate of 0.18 mm/rev (955 mm/min), hole depth of 30 mm (5diameter), and allowance of 0.2 mm. The lifetime of drills with the multilayer TiAlCrSiN coating was 2.01 times as long as that of the tools coated with single layer TiAlN and the multilayer TiAlSiN coatings. To investigate the differences observed in the performance of the coatings, the morphology of the outer corner flank was examined by SEM imaging. The wear patterns observed are shown in Figure 23. After drilling 1000 holes, the single layer TiAlN and multilayer TiAlSiN coatings showed considerable wear at the outer corner and margin of the drill bit (Figure 23a and b). Conversely, the multilayer TiAlCrSiN coated drill showed negligible wear at the outer corner and margin (Figure 23c). The superior drilling performance of the multilayer TiAlCrSiN coating compared with those of the single layer TiAlN and TiAlSiN coatings can be attributed to more favorable mechanical (high hardness) and tribological (low friction) properties, and wear resistance. The performance was likely enhanced by the incorporation of Cr into the multilayer TiAlSiN coating [19–22]. The low friction coefficient suggests that the decreased friction between the tool and chip in machining and a reduced tendency to stick and pick up material from the counterpart material, led to the extended service life of the

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TiAlN monolayer, TiAlN/SiNx, TiAlN/CNx, TiAlSiN, and TiAlCrSiN multilayer coatings were deposited on WC–Co carbide tools and silicon wafer substrates by reactive magnetron sputtering. We show that the multilayer structure affects the surface morphology, microstruc-

1. The introduction of a SiNx or a CNx layer leads to the formation of hard coatings owing to suppression of the TiAlN grain growth, grain refinement, and a decrease of the surface roughness. The morphology of the coating changed from a columnar structure to a fine-

2. The wear characteristics of the TiAlN/SiNx, TiAlN/CNx, TiAlSiN, and TiAlCrSiN multilayer coatings described in this study were improved compared with those of the TiAlN single layer coating. Furthermore, the tribological properties of the TiAlN and TiAlN/CNx coatings were improved owing to the deposition of CNx as the topmost layer, and the

3. The wear of the TiAlN/SiNx, TiAlN + CNx, and TiAlN/CNx + CNx coatings in sliding systems was considerably reduced with the use of water as a lubricant by approximately two orders of magnitude compared with the performance under dry conditions. The wear of the coating was considerably reduced for all coatings in SRV testing under PAO lubrication conditions compared with the results obtained under dry and water conditions.

cutting tool.

4. Conclusion

ture, mechanical, and tribological properties.

grained structure when SiNx and CNx layers were formed.

friction coefficients and size of wear scar of the coatings was decreased.

Figure 22. Outer corner wear of 6-mm diameter WC–co drills as a function of the number of holes drilled. Cutting speed: 100 m/min (5304 rpm), feed rate: 0.18 mm/rev. Workpiece: Carbon steel (S50C). Cutting fluid: Water soluble agent. Hole depth 30 mm (5diameter).

Figure 23. SEM images of the outer corner of worn areas of (a) TiAlN, (b) multilayer TiAlSiN, and (c) multilayer TiAlCrSiN coated 6 mm diameter WC–co drills after 1000-hole drilling test.

Figure 22. The performances of the multilayer TiAlSiN and TiAlCrSiN coatings were compared with that of the single layer TiAlN coating, which was used as reference. The drilling tests were performed on a drill-milling machine NH4000 (DMG MORI, Japan) at a cutting speed of 100 m/min (5304 rpm), feed rate of 0.18 mm/rev (955 mm/min), hole depth of 30 mm (5diameter), and allowance of 0.2 mm. The lifetime of drills with the multilayer TiAlCrSiN coating was 2.01 times as long as that of the tools coated with single layer TiAlN and the multilayer TiAlSiN coatings. To investigate the differences observed in the performance of the coatings, the morphology of the outer corner flank was examined by SEM imaging. The wear patterns observed are shown in Figure 23. After drilling 1000 holes, the single layer TiAlN and multilayer TiAlSiN coatings showed considerable wear at the outer corner and margin of the drill bit (Figure 23a and b). Conversely, the multilayer TiAlCrSiN coated drill showed negligible wear at the outer corner and margin (Figure 23c). The superior drilling performance of the multilayer TiAlCrSiN coating compared with those of the single layer TiAlN and TiAlSiN coatings can be attributed to more favorable mechanical (high hardness) and tribological (low friction) properties, and wear resistance. The performance was likely enhanced by the incorporation of Cr into the multilayer TiAlSiN coating [19–22]. The low friction coefficient suggests that the decreased friction between the tool and chip in machining and a reduced tendency to stick and pick up material from the counterpart material, led to the extended service life of the cutting tool.
