**4.1 Turning of X153CrMoV12 hardened steel with tool made of Al2O3-TiC and Al2O-SiCw mixed ceramics with Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating**

The structure of the Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating is depicted in **Figure 3** [67]. The total thickness of the coating is about 4 μm, and the nanolayer binary period λ is about 120 nm.

The chemical compositions of the coatings under study are presented in **Table 1**.

The coatings contain a similar amount of aluminum; however, the presence of Zr and Nb in the second coating causes some decrease in hardness with an increase in ductility, which makes it possible to provide a good level of resistance to brittle fracture [44, 46].

**Figure 4a** and **b** exhibit the results of the studies focused on the cutting properties of a tool equipped with (1) uncoated ceramic inserts made of Al2O3-TiC and Al2O3-SiCw ceramics, (2) Ti-(Ti,Al)N coating, and (3) Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating [67]. During the longitudinal turning of X153CrMoV12 hardened steel, the wear rate of ceramic tools based on mixed ceramics of Al2O3-TiC and Al2O3-SiCw depends rather largely on the coating composition. In particular, the maximum increase in the wear resistance of ceramic tools was provided by coatings based on the complex composite nanostructured system of Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N. At VB = 0.4 mm, the above system increases the tool life of a ceramic tool up to 1.5 times compared to an uncoated tool and by 1.3 times compared to a tool with the Ti-(Ti,Al)N commercial coating.

According to the studies of [1–4, 14–18], for a ceramic tool, the brittle fracture of its cutting edge is the most probable mechanism of failure. This fact can be explained by the lower brittle strength of the ceramic tool material in comparison with the same parameters of the carbide tool material. Ceramic tools also tend to stochastic brittle fracture because of the higher contact stresses, in particular, normal stresses. In general, the above contact stresses exceed the same values for carbide tools because of the considerable decrease in the total length of the contact between the chips and the rake face of the ceramic tool, at a small decrease in the normal load.

There are is a balance in the nature of wear centre development on the rake and flank faces of the Al2O3-TiC ceramic cutting insert with the Ti-(Ti,Al) N and Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coatings during the longitudinal turning of X153CrMoV12 hardened steel, with no visible chips and microchipping.

### **Figure 3.**

*Micro (a) and nano (b) structure of the cross-section for cutting Al2O3–TiC with Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coatings ceramic inserts [67](SEM).*


### **Table 1.**

*Chemical compositions of the coatings under study.*

### **Figure 4.**

*Relationship between wear VBmax and cutting time for (1) uncoated inserts, (2) tools with Ti-(Ti,Al)N coating, and (3) Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating, during the longitudinal turning of X153CrMoV12 hardened steel at vc = 250 m/min, f = 0.05 mm/rev, ap = 0.5 mm, inserts made of (a) Al2O3-TiC and (b) Al2O3- SiCw at vc = 300 m/min, f = 0.1 mm/rev, ap = 0.5 mm, inserts made of (b) Al2O-SiCw [67].*

### **Figure 5.**

*Wear pattern after 25 minutes in the longitudinal turning of X153CrMoV12 hardened steel at vc = 250 m/min, f = 0.05 mm/rev, ap = 0.5 mm for cutting inserts made of Al2O3-TiC with Ti-(Ti,Al)N [67] (SEM).*

Undisturbed residues of coatings at the edges of wear centres both on the rake and flank faces of the ceramic cutting insert are also typical for the process described above (**Figure 5a** and **b**) [67].

Both on the rake and flank faces of the tool, the wear mechanism typical for the Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating is primarily an abrasive interaction with the material being machined (**Figures 6** and **7**) [67]. It should be noted that the coating and the substrate work as a unified system, where cracks and chipping hardly occur. No adherents of the material being machined are detected on the coating surface, which may relate to the low adhesion between the external (wear-resistant) layer and the material being machined.

*Nanostructured Multilayer Composite Coatings for Cutting Tools DOI: http://dx.doi.org/10.5772/intechopen.94363*

During the cutting, good adhesion retains between the coating and the ceramic substrate (**Figure 7**) [67].

For the Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating, the typical mechanism of the coating failure is the formation of longitudinal cracks in the areas immediately adjacent to the cutting area (**Figure 8**) [67]. However, such cracks related to the delamination of the coating under the influence of the compressive residual stresses are much less dangerous compared to transverse cracks, often formed in monolithic coatings.

During the process of cutting with the ceramic tool with the Ti-(Ti,Al)N coating, massive adherents of the material being machined are formed, both on the rake and flank faces of the tool (**Figure 9**) [67]. The mechanism of tool wear relates to the adhesive-fatigue processes, which is confirmed by the nature of the coating failure with clear tear-outs of the coating elements (see **Figure 9**).

### **Figure 6.**

*Wear pattern on (a) rake face, (b) flank face, and (c) corner of the Al2O3-TiC ceramic insert with the Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating [67] (SEM).*

### **Figure 7.**

*Wear pattern on the rake face of the Al2O3-TiC ceramic insert with Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating [67] (SEM).*

### **Figure 8.**

*Ceramic insert of Al2O3-TiC with the Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N coating [67] (SEM).*

### **Figure 9.**

*Wear pattern (a) on the rake face of the Al2O3-TiC ceramic insert with the Ti-(Ti,Al)N coating and wear pattern (b) on the flank face of insert with particles of the material being machined after 20 minutes in longitudinal turning of X153CrMoV12 hardened steel at vc = 250 m/min, f = 0.05 mm/rev, ap = 0.5 mm [67] (SEM).*
