**3. Results and Discussion**

### *3.1. Coating Characterization*

In Figure 2, the coating's constitution can be observed, as well as the measurements performed to evaluate the total coating thickness.

**Figure 2.** (**a**) Coating SEM analysis: thickness measurements performed on the tool's cross-section; (**b**) Z1 corresponds to the EDS evaluation zone to characterize overall coating composition.

EDS analysis was performed to confirm the coating's chemical composition in the area indicated in Figure 2b. The spectrum obtained from this analysis can be observed in Figure 3.

**Figure 3.** EDS spectrum obtained from the tool coating analysis.

Observing Figure 2, it can be noticed that there was a zone with a lighter tone near the tool's substrate material. This is the TiN layer deposited close to the substrate, with a view to improving its adhesion and facilitating the deposition of further layers. However, in Figure 2, this layer is not clearly perceptible, and its composition could not be assessed by direct EDS analysis due to the interaction of the surrounding elements with the ones in this thin layer. As such, elemental mapping of the coated samples was performed, determining that this layer was in fact, the TiN layer. The base image used for the element mapping can be observed in Figure 4, while the element mapping that was performed can be observed in Figure 5.

**Figure 4.** Base image of the coating's cross-section used for element mapping.

**Figure 5.** Element mapping performed on the tool coating: (**a**) Al distribution, (**b**) W distribution, (**c**) Ti distribution, and (**d**) Al, W, and Ti distribution overlapped.

As observed in Figure 5c, there seems to be a line near the substrate that has a higher content of Ti when compared with the remaining coating. This is also evident in Figure 5d, where the Al seems to be present mainly on the coating's top layer, while the bottom layer

(near the substrate) is mainly composed of Ti. As such, it was determined that this was the layer composed of TiN.

Regarding the coating thickness, measurements were performed in various coated areas of the mounted tool samples, enabling the determination of the average coating thickness. These values are presented in Table 5, showing the average total coating thickness, as well as the average TiAlN and TiN layer thicknesses.

**Table 5.** Average thickness values for the complete TiAlN/TiN coating and its layers.


As seen from the figures presented in this subsection, this is a multilayer coating. The TiN sublayer promoted the adhesion of the coating to the substrate, thus improving its wear resistance and behavior when machining the workpiece. The method of employing a sublayer (not exclusively TiN) brings many advantages related to tool wear behavior improvement, as reported by many authors [43,44]. This sublayer, and in multilayered coatings overall, confers the coatings improved crack resistance and adhesion strength. This increases the coatings' wear behaviors, causing overall less sustained wear [10,17]. Not only are these sublayers related to an improvement regarding the tools' wear behavior, as they confer the tools improved oxidation resistance, which might prove useful when machining certain alloys, such as Inconel 718, as its cutting generates high punctual cutting temperature [37,38], but also they result in a high temperature concentrated in a very small zone in the tool–chip interface. The sustained tool wear and wear mechanisms will be assessed in detail in Section 3.3 of the present paper.
