## 3.1. X-Ray Diffraction Analysis

Previous research established optimum deposition conditions so that the hardness and adhesion of the coatings to the substrate would be adequate to obtain a good performance of the coatings, which implies the presence of lower residual stresses in the three coatings [7, 19–21]. From the analysis of the X-ray diffraction (XRD) patterns or diffractograms of the TiCN, BCN and CrAlN coatings, it was established that the three materials crystallized forming a NaCl-type FCC structure with space group Fm3m [4, 5]. Table 1 shows the lattice parameters and the full width at half maximum (FWHM) of the patterns. The results obtained for the TiCN, BCN and CrAlN coatings were 4.278 Å (SD = ± 0.096), 3.622 Å (SD = ± 0.028) and 4.334 Å (SD = ± 0.137), respectively.

Table 1

Lattice parameters and FWHM values of TiCN, BCN and CrAlN coatings, calculated from diffractograms

Lattice parameter and FWHM of the three coatings |

Coating type | TiCN (111) | BCN (111) | CrAlN (200) |

Ángulo 2θ (°) | 36,342 | 43,228 | 41,646 |

Ángulo θ (°) | 18,171 | 21,614 | 20,823 |

Parámetro de red ao (Å) | 4,278 | 3,622 | 4,334 |

FWHM (rad) | 0,8112 ± 0,0028 | 0,28978 ± 0,00192 | 0,29223 ± 0,00121 |

Figure 4a, shows the influence of the coating material on the FWHM; a decrease in peak width of the order of TiCN, CrAlN and BCN with values of 0.811, 0.292 and 0.289, respectively, was presented. The lateral crystallite size relationship as a function of coating material is shown in Fig. 4b. Eq. 1, called Scherrer's equation, is used to determine the crystallite size [7, 19, 22].

$${\text{D}}_{{\nu }}=\frac{\text{K}{\lambda }}{{\beta }\left(\text{cos}{\theta }\right)}$$

1

where *D**ν* is the crystallite size (Å), *K* is Scherrer constant that takes values between 0.81 and 1 (K = 0.9 was assumed for the present case), *λ* is the wavelength (1.5405 Å), *β* is the full width half maximum FWHM value in 2θ (rad), and *θ* is the Bragg diffraction angle (rad).

Based on the crystallite size results given in Fig. 4b, it can be observed that the TiCN coating has the lowest value, while the BCN coating has the highest value of lateral crystallite size; it can be established that TiCN presents greater obstacles for free crystallite growth compared to CrAlN and BCN. Previous studies determine mechanical and morphological properties of monolayers and multilayers that support these results for TiCN and CrAlN [7, 19, 20, 23, 22].

The influence of the type of coating material on the lattice deformation and biaxial deformation (biaxial stress) is shown in Fig. 5. Specifically, Fig. 5a presents the lattice deformation as a function of the coating material; Eq. 2 was used to determine this lattice deformation [24, 22].

$$\text{T}\text{tan}{\theta }=\frac{{\lambda }}{{\text{D}}_{{\nu }}\left(\text{cos}{\theta }\right)}-{\beta }$$

2

where *T* is the deformation of the lattice (Å).

From Fig. 5a, it can be concluded that all the deformations in the coatings were positive, producing tensile type stresses; a larger deformation was present in the TiCN coating, while a smaller lattice deformation was exhibited by the BCN coating. This agrees with the small shifts of peaks (111) and (200) to lower 2θ angles [5, 22]. Similarly, Fig. 5b presents the biaxial deformation (stress) in relation to the coating material, the deformation was determined by Eq. 3.

$${\epsilon }=\left(\frac{{\text{C}}_{\text{f}\text{i}\text{l}\text{m}}-{\text{C}}_{\text{b}\text{u}\text{l}\text{k}}}{{\text{C}}_{\text{b}\text{u}\text{l}\text{k}}}\right)$$

3

Where *ε* is the biaxial deformation (stress), *C**film* (ao real) is the constant or lattice parameter of the layer in orientation (111) or (200), given in the international index files (JCPDF) (Å) and *C**bulk* (ao calculated) is the lattice parameter corresponding to the monolayers grown with the different types of materials (Å).

The data obtained in the international index files (JCPDF) are considered to have no biaxial stress; under this consideration the biaxial stress produced in the deposited coatings can be calculated. By analyzing the results of Fig. 5b it can be established that the biaxial deformation in the planes varied according to the type of coating material. The values obtained are tensile type stresses in the following order: ε = − 3.1794x10− 3 for TiCN, ε = − 0.0110 for BCN and ε = -0.0447 for CrAlN.

## 3.2. X-Ray Photoelectron Spectroscopy

Table 2 shows the related X-Ray Diffraction and X-Ray Photoelectron Spectroscopy (XPS) results for all coatings [22]. For the XPS analysis, complete spectra were obtained for all three materials (see Fig. 6) [22]. The presence of high intensity peaks in each of the spectra allowed locating and defining the respective binding energies, facilitating the verification of the chemical composition and stoichiometry of the ternary layers. For TiCN: Ti (2p1/2) = 458.4, N (1s) = 396.80, C (1s) = 284.8 and Si (2p) = 61.6; for BCN: N (1s) = 400, C (1s) = 285.6 and B (1s) = 192.8; and for CrAlN: Cr (2p) = 475.99, N (1s) = 396.97, Al (2s) = 119 and Al (2p) = 74. Small amounts of oxygen can be evidenced in the graphs of the three coatings due to contamination from the presence of impurities. However, the low amount did not alter the stoichiometry and therefore did not affect the characteristics of the three coatings. Thus, the binding energy values found in the coatings together with the XRD results agree with the information reported in the references, confirming the formation of the three ternary compounds. [20, 25–27]. Finally, the stoichiometry for the coatings was determined: Ti32.45-C35.83-N31.72, B48.63-C31.22-N20.15 and Cr40.27-Al38.01-N21.72.

Table 2

Stoichiometric ratio and crystallographic characteristics for the three types of coatings TiCN, BCN and CrAlN

Coatings | Stoichiometric relation (XPS) | Crystalline structure (XRD) | Spacial group (XRD) | Lattice parameter ao (Å) (XRD) |

TiCN | Ti32C36N32 | FCC | 225-Fm3m | 4,278 |

BCN | B49C31N20 | FCC | 227-Fd3m | 3,622 |

CrAN | Cr40Al38N22 | FCC | 225-Fm3m | 4,334 |