## 3 Results
Wear distance-related plot of friction coefficient for Cr-Al-Ti-B-N coatings (Figure 5) demonstrates that the lowest friction coefficient (\(f=0.48\)) was achieved for P3 coating with 2 at.% boron. However, the friction was unstable, and after 90 m distance, the coefficient rose to 0.68-0.7. Boron-free coating P1 had a friction coefficient of 0.8 and suffered complete wear at 135 m. The coatings with the highest boron content demonstrated a drastic increase in friction coefficient (up to 0.8-0.9) during the first 20-30 m. Coating P4 with 2.3 at.% boron, which was characterized by max hardness, demonstrated a stable coefficient \(f=0.65\). This coating was the most wear-resistant and endured up to 200 m wear testing without complete wearing-out. Figure 4: The mechanical (**a**) and elastic-plastic (**b**) properties of coatings as a function of boron content. Figure 5: The plot of friction coefficients versus the wear distance for Cr–Al–Ti–B–N coatings. 3D profiles demonstrate the non-uniformity of the wear tracks (Figure 6). Therefore, the wear rate was calculated as the ratio on lengths of fully worn-out and partially worn-out fragments of the track. This calculation was applied for all coatings except the one with 2.3 at.% B, since its wear track had a constant depth and did not reach the substrate's surface. The wear rate (Figure 7) for boron-free coatings was \(8.8\times 10^{-5}\) mm\({}^{3}\)/(N\(\cdot\)m), whereas boron-rich coatings P5 (7.3 at.% B) and P6 (10 at.% B) had wear rates of \(6.9\times 10^{-5}\) mm\({}^{3}\)/(N\(\cdot\)m) and \(1.9\times 10^{-3}\) mm\({}^{3}\)/(N\(\cdot\)m), correspondingly. P4 coating with 2.3 at.% B had the lowest wear rate of \(7.5\times 10^{-6}\) mm\({}^{3}\)/(N\(\cdot\)m). Figure 6: 3D profiles of wear tracks for the coatings with varied boron content: (**a**)—0 at.%; (**b**)—2 at.%; (**c**)—2.3 at.%; (**d**)—10 at.%. Figure 7: Specific wear of Cr–Al–Ti–B–N coatings. 2D and 3D images of the wear tracks (Figure 8) demonstrate that all coatings except coating P4 experience a full wear-out, with the wear track depth exceeding the width of the coatings. In the case of specimen P4, the wear is partial, with the fragments of pristine coatings present along with partially-worn segments. Since the geometrical estimation of wear tracks is unviable, the resistance towards abrasion was estimated by the weight loss during abrasive testing (Figure 9). Maximal weight loss of 0.42 micrograms was recorded for boron-free P1 coating. All boron-containing coatings demonstrated substantially lower weight loss (0.04-0.10 micrograms). The lowest value of 0.04 micrograms was characteristic for P4 coating. The free corrosion potential of coatings in H\({}_{2}\)SO\({}_{4}\) after 30 min exposure was in the 0.310-0.808 V diapason (Table 2). The potential decreased at higher boron content. The initial section of anode polarization curves (Figure 10) is the most characteristic of the coating's working conditions. The current density (Table 2) was calculated assuming that Ti and Cr are dissolved in solution mainly as the bivalent ions. Figure 8: 2D (**a,d**) and 3D (**b,c**) profiles of worn zones for coatings with 0 (**a,b**) and 2.3 (**c,d**) at.% of boron after the abrasive test. Figure 9: Mass loss after the abrasive test. For the Cr-Al-Ti-N coating, the max current density was \(\sim\)140 nA/cm\({}^{2}\). The introduction of boron even in minimal quantities results in a 10-fold decrease in the current density. The minimal density of 18 nA/cm\({}^{2}\) was achieved for the coating with 2.3 at.% B. An increase of boron content to 7-10 at.% yields a 1.5-2 times increase in the current density as compared to 2.3 at.% B. The second part of the work was dedicated to the development of the upper decorative Cr-Al-Ti-B-O-N layer. Data on the chemical compositions, width, and coloration of the layers are summarized in Table 3. Figures 11 and 12 provide photos of coated specimens.