**5. Deposition of nanoscale composite multilayer coatings (NMCC)**

 Nanoscale composite multilayer coatings were deposited on carbide inserts using filtered cathodic vacuum arc deposition (FCVAD) with the vacuum-arc unit VIT-2 [9, 10, 12, 13, 19]. The study used a three-component nanoscale composite multilayer coatings (NMCC) system, comprising outer (wearresistant) layer, intermediate layer, and adhesive layer. The developed threecomponent NMCCs meet at best the dual nature of coatings as an intermediate process medium between the tool material and the material being machined. The coating should at the same time increase the physical and mechanical properties of the cutting tool (hardness, heat resistance, wear resistance) and reduce thermal and mechanical effect on the contact pads, resulting in their wear. The analysis of the influence of the synthesis process parameters on various properties of composite coatings (e.g., Ti-TiN-TiCrAlN) has shown that the most important parameters are as follows: current of titanium cathode arc ITi., nitrogen pressure in vacuum chamber pN, and bias potential on the substrate (tool) during condensation of wear-resistant layer Uk. These parameters were taken as major ones for the deposition of NMCCs.

The investigation into the microstructure of NMCCs was carried out on a Jeol electron scanning microscope JSM-6480LV. The macroscopic properties of NMCCs, such as thickness, hardness, friction coefficient, and strength of coating adhesion to substrate, were determined by standard methods.

Using a portable computer tomography UPUC-2000, the temperature gradient of the developed tool system was obtained as shown in **Figure 10**. Here, a reduction in the intensity of the heat source in the NMCC can be seen with a better heat dissipation through the thermal pad.

 The certification (industrial confirmation) tests of the developed tool system were carried out in turning of running surfaces of wheel sets. The tests were conducted with carbide inserts (14% TiC, 8% Co, 78% WC) without coatings, and with inserts coated with the developed Ti-TiN-TiCrAlN NMCCs. Tests were performed on the heavy machines of Rafamet UCB-125 bUBB112, the criterion of insert failure was flank wear VBmax = 0.5 mm.

#### **Figure 10.**

*A general view of heat distribution in the cutting zone at cutting speed vc = 40 m/min, ap = 3 mm, f = 1.0 mm/ rev [19]; a—commercial carbide inserts with multilayer coatings of modern generation and b—newly developed tool system.* 

#### **Figure 11.**

*SEM section image of (WC-TiC-Co) carbide insert with NMCC based on Ti-TiN-TiCrAlN [19]: 1—TiCrAlN wear-resistant layer, 2—TiN intermediate (transition) layer, 3—Ti adhesive sublayer, and 4—carbide substrate (14% TiC, 8% Co, and 78% WC).* 

The properties of NMCCs base on the Ti-TiN-TiCrAlN system are illustrated in **Figure 11** and in **Table 1**.

The Ti-TiN-TiCrAlN multilayer composite coating was deposited with the following process parameters: ITi = 104 A, pN = 0.24 Pa, UC = 42 V, and deposition time = 45 min. The analysis of the data presented in **Table 1** shows the following.

 Wear-resistant layer of TiCrAlN of the tested NMCC based on the Ti-TiN-TiCrAlN system has a super multilayer architecture with sublayer thicknesses of about 15–25 nm, a columnar grain structure oriented perpendicular to the plane of TiN underlayer, in which grain sizes do not exceed 5–15 nm. The thicknesses of the sublayers of the intermediate TiN layer were also about 15–25 nm, and the sizes of its grains, as well as of grains of adhesion sublayers, did not exceed 5–15 nm. The results obtained allow classifying the multilayer composite coating of Ti-TiN-TiCrAlN as a nanocoating. The use of a vacuum arc system with filtration of vapor-ion flow FCVAD provided a significant increase in the quality of the surface of NMCC and almost a complete absence of droplets (which are dangerous defects) on the surface of the coating. This study revealed a high efficiency of the developed tool system based on double-sided (WC-TiC-Co) carbide inserts (see **Figure 8a**), with dense contact with tool holder, provided by elastic pads of reinforced ceramicpolymer material with high thermal conductivity. Tool life and coefficient of tool life variation for the developed tool system were compared with commercial tool equipped with carbide inserts with multilayer coating of the modern generation. The tool life coefficient TTL (**Figure 12**) was determined as the ratio of tool life


#### **Table 1.**

*Test results of NMCC parameters (on the example of Ti-TiN-TiCrAlN system).* 

#### **Figure 12.**

*Results of comparison of tool life coefficient TTL and tool life variation υ of the developed tool system with commercial carbide inserts with coatings in rough turning of wheel sets [19]; process parameters: vc = 50 m/min, f = 1.2 mm/rev, and ap = 6.0 mm. 1—developed tool system and 2—commercial carbide inserts with modern multilayer coatings.* 

 of coated insert to tool life of an uncoated insert; and the tool life variation υ was determined as the ratio of standard deviation of tool life to its arithmetic mean value. The study showed that the developed tool system based on inserts of carbide (WC-TiC-Co) with Ti-TiN-TiCrAlN NMCCs outperformed the commercial version of carbide insert with coating of the modern generation during hard reconstruction turning of running surfaces of wheel sets (**Figure 12**). In particular, the study has shown not only the higher average tool life value (88.1 min) and tool life coefficient TTL (2.1), but also the decrease in the coefficient of tool life variation (υ = 0.355). The latter indicates the significant increase in the reliability of the developed tool system for rough turning of wheel sets.

The results of production tests of carbide cutting tools with the use of thermal pads made of NOMAKON KPTD-2 are shown in **Table 2**. The analysis of the results of the production tests also shows the increase in tool life in the developed tool system.


 *A—turning-and-contouring machining of surface of neck, wheel seat and middle part of axes and B—turning-andcontouring machining along outer diameter.* 

#### **Table 2.**

*Results of industrial tests of 14% TiC; 8% Co; 78% WC carbide inserts with NMCC and thermal pad.* 

#### **Figure 13.**

*Wear of carbide insert LNUX 301940 [19]: (a, c) rake, (b, d) flank, (a, b) without thermal pad, intensive plastic deformation of cutting edge, leading to cracking and brittle fracture—(zone A). (c, d) with thermal pad, less pronounced plastic deformation, mainly flank wear [2].* 

The effect of applied thermal pad on the nature of the wear of rake and flank faces is illustrated in **Figure 13**.

 Additional tests were done with inserts AT15S carbide type LNUX 301940. These carbides were composed of 86.5% WC, 2.5% TiC, 3.6% TaC, 1.5% NbC, 5.5% Co. These tests showed a significant effect of the applied thermal pad, and the NMCC in turning of wheel sets. This is depicted in **Figure 14**.

 1—uncoated inserts without thermal pad, 2—uncoated inserts with thermal pad, 3—inserts with TiN (PVD) coating, without thermal pad, 4—inserts with TiN (PVD) coating, with thermal pad, 5—inserts with Ti-TiN-TiCrAlN NMCC, without thermal pad, and 6—inserts with Ti-TiN-TiCrAlN NMCC, with thermal pad.

 The studies were carried out under turning of running surface of wheel pair with vc = 50 m/min, f = 1.2 mm/rev, and ap = 6.0 mm (presented in **Figure 15**).

#### **Figure 14.**

*Average tool life of one insert with eight cutting edges for carbide inserts type LNUX 301940, carbide AT15S [19] (process parameters: v = 50 m/min, f and = 1.2 mm/rev, and ap = 6.0 mm) [2].* 

#### **Figure 15.**

*Results of comparative tool life tests CLT and variations of tool life υLT of the carbide inserts with standard coating of leading manufacturers (2–4) and the inserts made of carbide WC-TiC-Co with high thermal conductivity and developed NMCC (1) under rough turning of railway wheel sets [19]. 1—inserts with high thermal conductivity and developed Ti-TiN-TiAlN (technology FCVAD), 2—inserts with standard multilayered composite coating TiN-TiCN-TiN (CVD, manufacture 2), 3—inserts with standard coating TiCN-Al2O3-TiN (HT-CVD, manufacture 3), and 4—inserts with standard coating TiC-TiCN-TiN (HT-CVD, manufacture 4).* 

 Evaluation of the working efficiency of cutting inserts was performed by the coefficient of wear resistance relative to the reference inserts of WC-TiC-Co without coating, in which wear resistance was taken as a unit under tests with the specified machining modes with limited flank wear land HV = 0.5 mm. The comparison was made with carbide inserts of best manufacturers with standard coatings and inserts with generated interface improving the thermal conductivity of the cemented carbide and developed NMCC.

 The analysis of the studies presented in **Figure 15** allows noting the following. The analysis proved high efficiency of carbide cutting inserts in the form LNMX made of carbide grade WC-TiC-Co with thermally conductive interface and developed NMCC on the basis of a three-layer system of Ti-TiN-(Ti,Al)N in comparison with standard analogues under severe reductive turning of running surface of wheel pairs. In particular, the analysis notes not only the higher average value of lifetime of carbide tool (88.1 min) and the lifetime coefficient CLT(2.10), but also

*Main Ways to Improve Cutting Tools for Machine Wheel Tread Profile DOI: http://dx.doi.org/10.5772/intechopen.80302* 

reduction of the factor of a variation of lifetime (υLT = 0.35). This indicates the significant increase in working efficiency and reliability of the tool equipped with tangential carbide inserts LNMX made of WC-TiC-Co with enhanced thermal conductivity of carbide with elaborated NMCC on the basis of the system Ti-TiN-TiAlN developed for reductive turning (roughing) of hardened (hard-drawn) surface of wheel pairs [2].
