*3.2.1 Chemical study for TiCN, BCN and CrAlN coatings nitride coatings*

**Figure 4** shows the survey spectra for the TiCN, BCN and CrAlN coatings. These spectra presented high intensity peaks where their location with their

**Figure 4.** *XPS survey results for the three coatings used: (a) TiCN, (b) BCN and (c) CrAlN.*

*Analysis of the Tribological Evolution of Nitride-Based Coatings DOI: http://dx.doi.org/10.5772/intechopen.100629*

respective binding energies were determined. For the TiCN coating, Ti (2p3), C (1 s) and Si (2p) peaks located at the binding energy 458.4 eV; 396.8 eV; 284.8 eV and 61.6 eV respectively were obtained; for the BCN coating, N (1 s), C (1 s) and B (1 s) peaks located at the binding energy 400 eV; 285.6 eV and 192.8 eV respectively were obtained; and for the CrAlN coating Cr (2p), N(1 s), Al (2 s) and Al (2p) peaks located at the binding energy 475.99 eV; 396.97 eV; 119 eV and 74 eV respectively were obtained. Previous studies indicated that the signals of C (1 s) and N (1 s) are associated with C-N and Ti-N bonds, these results are agreement with the literature [16]. Analysis of the XPS spectra for the BCN coating showed the binding energies corresponding to the N (1 s), C (1 s) and B (1 s) signals were consistent to the formation of the BCN ternary compound as corroborated in the literature [17]. For the ternary CrAlN coating, Cr (2p3/2), Al (2p) and N (1 s) signals associated with Cr-Al bonds were presented, binding energies for Cr-N and Al-N were also evidenced, confirming the formation of the ternary CrAlN compound [18]. Finally, the stoichiometry was determined for all the coatings (Ti32.45-C35.83-N31.72, B48.63- C31.22-N20.15 and Cr40.27-Al38.01-N21.72).

### *3.2.2 Chemical study for Si3N4 nitride coatings*

**Figure 5a** show the depth spectra for the Si3N4 coating, showing the spectral lines of the elements present in the coating by X-ray photoelectron spectroscopy (XPS) technique. From this result, elements such as Si and N, and elements in low quantity such as Oxygen were found. In order to know the detailed surface stoichiometry of the coating, the high resolution XPS spectra of Si-2p and N-1 s species are also presented in the **Figure 5b** and **c** respectively. The Si3N4 coating has an atomic N/Si ratio of 1.32 (stoichiometry *Si*57*N*43). The Si3N4 has an ideal stoichiometry ratio of 1.33 which is in agreement with what is found in the literature. In addition, the

#### **Figure 5.**

*Depth spectra obtained by the XPS technique for the Si3N4 nitride coatings and high resolution XPS spectra for the Si3N4 coating: (a) Si-2p signal; (b) N-1s signal.*

high-resolution Si-2p spectrum (**Figure 5b**) presented two peaks located at a binding energy of 101.77 eV and 104.88 eV, respectively. These two peaks are attributed the Si-O and Si-N bonds of the Si3N4 [19]. On the other hand, **Figure 5c** shows the high-resolution spectrum for the N-1 s peak, which id fitted by three peaks. The first peak, corresponding to (N-O) bond, located at a binding energy 400.51 eV [20]; the second peak, corresponding to the (N-Si) bond, located at a binding energy of 396.96 eV, and the third peak, can be attributed to a different chemical state of N due to its different bonding configurations with neighboring atoms such as H and C located at a binding energy of 394.4 eV [21].

### **3.3 Morphological comparison between nitride coatings**

#### *3.3.1 Morphological study for TiN and TiCrN nitride coatings*

To quantitatively study the surface morphology of the samples, the atomic force microscopy (AFM) technique was used. **Figure 6a** and **b** present the images corresponding to titanium nitride (TiN) and titanium chromium nitride (TiCrN) respectively. From these results, it was evident that the TiCrN surface has a more regular surface compared to TiN. This surface change is attributed to the incorporation of chromium (Cr) into its crystalline structure, which causes a compressive deformation, making a much denser and compact structure with a more orderly growth.

**Figure 4c** and **d** show the roughness and grain size for the TiN and TiCrN layers and the [TiN/TiCrN] based multilayer system as a function of the bilayers number n = 1, 25 and 50 respectively. These results indicated that the TiCrN layer presented better surface properties (roughness and grain size) compared to the TiN layer. In addition, by means of the multilayer system, it was evidenced that by increasing the bilayers number or interfaces, the surfaces presented a lower number of imperfections due to the fact that the system becomes much denser generating a more regular surface, because an increase in the density of the system is promoted due to a higher number of interfaces. Authors such as J.C. Caicedo et al. [22] also showed this behavior in multilayer systems. In addition, the roughness is a factor that influenced the tribological properties, influencing the formation of asperities, the type of contact and the wear generated at the beginning of the tribological test [23, 24].

#### *3.3.2 Morphological study for TiCN, BCN and CrAlN coatings nitride coatings*

Using SPIP® statical analysis software, AFM images were obtained in contact mode (**Figure 7a**–**c**). From these images, the surface roughness and grain size values of each coating were obtained (**Figure 8a** and **b**). From these images it can be clearly observed the change in surface morphology as the nature of the coating changes, taking into account that the three materials have a similar thickness.

**Figure 6.** *Atomic force microscopy for single layer coatings: (a) TiCrN and (b) TiN.*

*Analysis of the Tribological Evolution of Nitride-Based Coatings DOI: http://dx.doi.org/10.5772/intechopen.100629*

**Figure 7.** *AFM images for all coatings: (a) TiCN, (b) CrAlN and (c) BCN.*

#### **Figure 8.**

*Influence of TiCN, BCN and CrAlN coatings' nature on morphological surface: (a) roughness as a function of coating materials, (b) grain size as a function of coating materials.*

**Figure 8** shows the relationship between surface roughness and grain size. These results indicated that the TiCN coating presented the higher values for roughness = 7.01 μm and grain size = 62.6 μm; followed by the CrAlN coating, which presented roughness = 6.47 μm and grain size = 58.8 μm. Finally, the BCN coating presented the best characteristics (lowest values) of roughness = 4.12 μm and grain size = 51.6 μm. Thus, there was a decrease of 41.23% and 17.57% for roughness and grain size respectively. From the results obtained by AFM, it was observed that the BCN coating presented the best results, which is due to the susceptibility of BCN to grow with low roughness on the substrate with respect to the other coatings, also producing the reduction of the grain size (which is directly proportional to the reduction of the roughness), causing a more compact coating to be generated.

#### *3.3.3 Morphological study for Si3N4 coatings nitride coatings*

**Figure 9** presents the AFM images of the Si3N4 coating, where it was determined that the coating presented a grain morphology with circular geometry with a low grain size and a homogeneous surface. This surface characteristic is attributed to a high ionic bombardment of Ar+ atoms generated during the deposition process, which modifies the surface morphology of the coating. Thus, ion bombardment causes an increase in the energy of the atoms adsorbed on the substrate surface, generating an increase in the nucleation sites. This results in a reduction of grain size, roughness and columnar growth, as well as an increase in the density of the coatings [5, 25]. **Figure 9b** shows the values of the roughness and grain size for

#### **Figure 9.**

*Atomic force microscopy (AFM) images for the single layer Si3N4 coatings, showing the morphological analysis of the Si3N4 coatings: roughness and grain size.*

the coating, where it was determined that the Si3N4 surface presented optimal results, so these morphological characteristics will greatly affect the mechanical and tribological properties of this coating.

#### **3.4 Mechanical properties comparison between nitride coatings**

#### *3.4.1 Mechanical properties for TiN and TiCrN nitride coatings*

**Figure 10** shows the load-depth curves obtained during the nanoindentation test fir the TiN and TiCrN single layer coating and the TiN/TiCrN multilayer system as a function of the bilayers number. These results showed a higher penetration fir the substrate (steel H13). In addition, the TiCrN layer showed a lower penetration compared to the TiN layer and for the multilayer system, there was a decrease in penetration as the bilayers number increased. This behavior is due to the surface properties of each coating as corroborated in the **Figure 10b** and **c**. Thus, **Figure 10b** and **c** shows the values of hardness (H) and elastic modulus (E) for the individual coating and multilayers system (TiN, TiCrN and [TiN/TiCrN]) where it was determined that both presented hardness higher than 10 Gpa, which serves as a parameter to qualify them as hard coatings, which allows to have a longer life time and lower wear rates in cutting tools that implement this type of coatings [26]. Finally, these results show a hardness of 18.5 Gpa and an elastic modulus 284.17 Mpa, as well as a hardness of 20.35 Gpa and elastic modulus 314.2 Mpa for the TiN and TiCrN single layers, respectively.

#### **Figure 10.**

*Nanoindentation results (a) Load-displacement curves for the TiN and TiCrN single layers; (b) Hardness and (c) Elastic modulus values.*

The TiCrN single layer showed better properties due to the higher compressive stresses generated in the coating during the sputtering of the deposition process [22].
