2.3. Mechanical and tribological properties evaluation

Mechanical properties, including hardness and adhesion strength were measured by Vickers hardness and scratch testing (CSM Instruments SA). The load used for hardness measurements was 0.025 N. A scratch tester was used to apply an increasing load with a spherical diamond indenter having a radius of approximately 0.2 mm. The critical load Lc, determined by acoustic emission (AE) observations of the scratch, was used as a quantitative measurement. Full details of the methods used in the hardness and scratch tests have been previously reported [4].

The tribological properties were evaluated from pin-on-disc friction and SRV testing methods. The pin-on-disc wear test was performed at an air humidity of 50 10% and a temperature of

Figure 3. Swing type friction tester (SRV).

cleaning process, Ar ions were directed at the substrate with a substrate bias of 500 V. Subsequently, the multi-component multi-nanolayer films were coated with a gas mixture of Ar (220 ml) and N2 (160 ml). On the basis of preliminary experiments, the optimal deposition parameters were determined and multilayer coatings were fabricated. To compare the frictional properties of the monolayer and multilayer coatings, the total film thickness of the TiAlN, or TiAlN/CNx layers was set to be 3 μm. The CNx top layer was approximately 0.5 μm. For multilayer coatings, the layer period was set to be approximately 7 nm and the thickness of the TiAlN layer was

approximately 6 nm [4, 7].

Figure 2. Samples of mono- and multilayer coatings.

Figure 1. Schematic of DC sputtering equipment.

80 Lubrication - Tribology, Lubricants and Additives

25 3C with the use of a pin-on-disc tribometer with a counterpart composed of SUS304 steel, placed horizontally on a turntable. The wear test was performed at a load of 0.5 N and a linear speed of 100 mm/s for a total sliding time of 600 s (corresponding to a sliding distance of 60 m). The frictional coefficients were calculated by measuring the frictional force from the wear scar area. In the SRV tests, the two test specimens, namely balls and discs, were installed in the test chamber and pressed together. As shown in Figure 3, the upper specimen was oscillated over the lower specimen at pre-programmed frequency, stroke, load, and temperature settings. In this study, the test was conducted with the use of an AISI440C ball indenter (SUS440C, 6.0 mm diameter) without lubricant under a 10 N load, with the use of a 500-μm stroke, a 50-Hz frequency, and 30,000 revolutions at room temperature and atmospheric pressure (30–45% humidity). The wear profiles of the coatings were measured by the SRV test.

of TiAlN/SiNx, as shown in Figure 4b. This effect could be attributed to growth of the primary nuclei on the top layer (Figure 4b). This result indicates that growth of crystals was blocked periodically by the development of the surface covering layer, which covered the whole surface of the crystals and suppressed grain growth [4, 7, 23]. Figure 4c shows a SEM image of a fracture cross-section of a TiAlN/CNx coating. The TiAlN/CNx also showed a fine-grained

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

http://dx.doi.org/10.5772/intechopen.73141

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Figure 5 shows TEM images of the microstructure of a TiAlN/SiNx multilayer film. The TiAlN/ SiNx was formed by alternation of the TiAlN and SiNx layers at a rotation speed of 3 revolution per minute (rpm) [4]. A nanolayered structure composed of sequentially alternating TiAlN and SiNx layers was confirmed [4]. High resolution TEM images of the TiAlN/SiNx nanolayer cross-section exhibited a bilayer period of 6–8 nm and nanometer-sized grains. The white arrows in the figure indicate the film growth direction. The film morphology showed a dense

Figure 6 shows a TEM image of the microstructure of a TiAlN/CNx+CNx multilayer film. As shown in area I (Figure 6a, marked by an arrow), the bright dots indicate the presence of a CNx top layer phase with a uniform amorphous structure. In areas II and III of Figure 6a (indicated by arrows), micro-diffraction patterns featured both individual spots and continuous rings that corresponded to the superposition of individual diffraction patterns of TiAlN and CNx [7]. Figure 6b shows that the film morphology was fine-grained and that the growth directions of the TiAlN and CNx layers alternated, as indicated by the dark and bright layers, respectively. Figure 6c shows that the TiAlN nanolayers in the TiAlN/CNx coating were approximately 5-nm thick and separated by a matrix of amorphous carbon [4]. This result suggests that the TiAlN/CNx multilayer had a modulated structure with a periodicity of approximately 7 nm, indicating that the nanolayered structure was composed of sequentially

structure owing to the introduction of CNx into the coating system [7].

alternating TiAlN/CNx, owing to the rotation speed of 3 rpm [4, 7, 23, 24].

Figure 5. Cross-sectional TEM images of TiAlN/SiN coating, observed at scale of (a) 500 nm and (b) 7 nm.

columnar structure.
