**3. Comparison between nitride coatings**

### **3.1 Structural study for TiN and TiCrN nitride coatings**

**Figure 1** shows the diffraction patterns for the initial coating based on (TiN), where diffraction peaks located in the crystallographic planes (111) (200, 220), (311), (222) and (400) were obtained. In addition, the incorporation of Cr atoms within its structure for the formation of the coating (TiCrN), which still shows the same characteristics peaks. On the other hand, the displacement of the characteristics peaks of the multilayer system formed by [TiN/TiCrN] can be evidenced as a function of the increase in the bilayers number deposited on Si substrates (100). Determining that the increase in the number of interfaces causes a distortion of the crystalline structure due to residual stresses within this multilayers system, which will influence the mechanical and tribological properties of this type of coatings. From these results it was possible to infer that all coatings have a face-centered cubic crystal structure (FCC) [5, 10].

#### *3.1.1 Structural study for TiCN, BCN and CrAlN coatings nitride coatings*

**Figure 2** shows the X-ray diffraction patterns for more complex coatings such as TiCN, BCN and CrAlN coatings. From these results, 2θ diffraction sequences were evident for face-centered cubic (FCC), NaCl type structures with and Fm3m space group [11]. The conformation of this type of coatings (TiCN, BCN and CrAlN) is associated by the substitution mechanism, in which, the carbon atoms (C) substitute the nitrogen atoms (N), giving rise the ordered CN systems in Ti, B and unordered for TiCN and BCN coatings. On the other hand, the CrAlN coating is the result of the coupling the two FCC phases of AlN and CrN, which generated a conjugated complex, where Al and Cr atoms are located in reticular positions and aluminum atoms (Al) are substituted by atoms of (Cr) while nitrogen atoms are located in the interstitial position of the CrAlN crystal [12–14]. Through these results, a NaCl-type FCC structure was determined for the three coatings, in which Ti, B, Cr and Al atoms would be located at the Wyckoff 4a site and the Wyckoff 4b site is randomly occupied by C and N atoms. Thus, titanium carbon-nitride as well as boron carbo-nitride are agreement with the international indexing files JCPDF 00-042-1488 and JCPDF

#### **Figure 1.**

*X-ray diffraction patterns for monolayers [TiN and TiCrN] and multilayers [TiN/TiCrN]n as a function of the number of bilayers 1, 25, and 50.*

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

#### **Figure 2.**

*Diffraction patterns for all coatings: (a) TiCN, (b) BCN and (c) CrAlN. Dotted lines indicate the peaks position obtained from the international indexing files (JCPDF) of TiCN, BCN and CrN–AlN respectively.*

00-035-1293, while for aluminum chromium nitride two indexing are performed, taking into account the structure of chromium nitride (CrN) JCPDF 00-003-1157 and aluminum nitride (AlN) JCPD 00-025-1495 [15]. In addition, it can be observed that the CrAlN coating is constituted by CrN and AlN, which present the same NaCl-type FCC crystal structure and a 225-Fm3m space group. These results established that the higher intensity peak (111) located at the for angles 2θ = 36.342° and 43.228° for TiCN and BCN coatings respectively. Otherwise, for the CrAlN coating, where the peak of higher intensity (200) was located at angle 2θ = 41.646°. Finally, shifts towards smaller 2θ angles relative to the positions where the material is stress-free (dotted line). These shifts of the diffraction peaks suggest a variation of the lattice parameter of the crystal structures of the coatings. Considering that TiCN, CrAlN and BCN coatings present cubic structures, it can be observed that when the value of the theta angle (θ) decreases, the lattice parameter increases, evidencing an increase of the internal stresses (compression type) within the crystalline structure of the coatings.

#### *3.1.2 Structural study for Si3N4 nitride coatings*

**Figure 3** shows the XRD diffraction patterns for Si3N4 coating deposited on silicon (100), where diffraction peaks located in the (111), (220), (311), (400), (511), (440) and (533) crystallographic planes characteristics of a face-centered cubic structure FCC were obtained. In addition, a preferential texturization is observed in the (311)

**Figure 3.** *Diffraction patterns of the Si3N4 single layers coating deposited on silicon.*

plane, it was also observed that the peaks presented horizontal displacements at 2θ with respect to those reported in the JCPDC 00-051-1334 file (dotted line), were caused by internal stresses generated during the deposition process, which caused a deformation in the crystallographic planes of the structure of the coatings.
