3.5.1. T1—Wear Mechanism Analysis

Here, the images taken from the SEM analysis regarding the T1 tools are presented. The main types of wear that these tools sustained were abrasive wear, coating cracking and delamination, exhibiting some adhesion of machined material. As expected, there was an influence on wear severity caused by the increase in cutting length, as can be observed in Figure 4.

**Figure 4.** Clearance face, with a 500× magnification, of the T1L2F100 (**a**) and T1L4F100 (**b**) tools, and rake face, with a 500× magnification, of the T1L2F100 (**c**) and T1L4F100 (**d**) tools.

As seen in Figure 4, the wear was more severe for the 4-m cutting length machining tests, with these exhibiting more damage to the flank and the presence of well-developed wear mechanisms, such as machined material adhesion. The machined material adheres to the tool's surface overtime, promoting the development of wear mechanisms such as abrasion, coating delamination and adhesive wear. The adhesion present in the rake face of the T1L4F100 tool is presented with larger magnification in Figure 5.

**Figure 5.** Adhered workpiece material present in the T1L4F100 tool's rake face, with a magnification of 2500×.

The adhesive damage observed in Figure 5 was analyzed to determine if the material present on the surface was the one that was being machined. Thus, EDS analyses were performed to determine the chemical composition of the damage, as observed in Figure 6. It was indeed confirmed that the adhered material was the DSS, as its chemical composition was very close to that supplied by the manufacturer. Therefore, it can be concluded that the increase in cutting length promotes the adhesion of machined material to the tool's surface and that there is a lower amount of adhered material for the T1L2F100 condition, as seen in Figure 4c.

Regarding the influence of feed rate on the tools' wear and registered mechanisms, although there was an influence on the amount of wear that was sustained by the tools, the identified mechanisms were present in all the tested conditions, albeit in different levels of severity. In Figure 7, the tools' rake and clearance faces are depicted for the 75% and 125% feed conditions.

In Figure 7, it can clearly be observed that both the 75% feed rate condition and the 125% feed rate condition produced a more severe wear than that registered for the 100% feed rate (Figure 4); this was also observed in the previous section with the values of flank wear.

As previously mentioned, the main wear mechanisms that were detected during the analysis of this tool were abrasion, coating cracking, delamination and some adhesion. These are common wear mechanisms that are developed when machining DSS alloys [45,46]. Some evidence of abrasion can be observed in Figure 8.

**Figure 6.** Rake face of the T1L4F100 tool with the various zones picked for analysis (**a**), and analysis of zone 3 (Z3), where there are signs of adhesion (**b**).

As seen in Figure 8, for a test conducted at a 2-m cutting length, there were already parts of the tool's rake face with exposed substrate. There were abrasion marks, as pointed to in the picture. This was concluded to be due to the thinning of the coating in the marked area. Furthermore, there was evidence of coating spalling in the area pointed to in Figure 8. Regarding the adhered material, material adhesion was promoted by an increase in cutting length, as Figure 8 shows that the material tended to adhere to the machining grooves present in the substrate, promoting abrasive wear in that area and eventually leading to coating delamination. Some cracking in the tool's coating was also registered, especially

under the conditions of a lower feed rate, which can be observed in Figure 4. In Figure 9, this cracking process can be observed in a more detailed manner.

**Figure 7.** Clearance face, with a 500× magnification, of the T1L2F75 (**a**) and T1L2F125 (**b**) tools, and rake face, with a 500× magnification, of the T1L2F75 (**c**) and T1L2F125 (**d**) tools.

**Figure 8.** Wear mechanism analysis of the T1L2F125 rake face.

**Figure 9.** Coating cracking present on the tool's clearance face for the T1L2F75.
