3.6.2. Flank Wear Measurement Summary

In the present subsection, all the calculated average values of flank wear, measured on the clearance faces of all the tested tools, are discussed. As seen in the section regarding surface roughness analysis, all the collected values are presented in graphical form in Figures 22 and 23.

**Figure 21.** Average values of Ra, measured in the radial direction for T1, T2, T3 and T4 tools, for the test conditions conducted at 2-m cutting length (**a**); and 4-m cutting length (**b**).

**Figure 22.** Average values of VB, measured on the clearance faces of the T1, T2, T3 and T4 tools, for all the different test conditions.

**Figure 23.** Average values of VB, measured on the clearance faces of the T1, T2, T3 and T4 tools, for the test conditions conducted at 2-m cutting length (**a**); and 4-m cutting length (**b**).

In Figures 22 and 23, a clear increase in wear with an increase in cutting length and feed rate was clearly observed for T1 and T2 tools. Furthermore, T1 tools seemed to be the most affected, in terms of wear, by feed rate variation (positive or negative), whereas T2 seemed to be the most affected by the variation in cutting length, especially at higher feed rate values. Regarding tools T3 and T4, these showed the most wear of all tools for the original feed rate conditions, with T3 being slightly affected by cutting length variation, andT4 being significantly more affected by the variation of this parameter at a 100% feed rate. However, T3 and T4 tools produced low wear for the lower feed rate values, producing, as well, the lowest amount of flank wear registered for the high feed rate test conditions. In fact, the wear presented by these tools was minimal for these test conditions, indicating that in terms of wear behavior these would be more suited for the machining of this material, especially at high feed values. Regarding once again tools T1 and T2, although these produced the best behavior at the original feed rate, and T2 even registered the second lowest values for flank wear tested under the condition of a 2-m cutting length and 75% feed rate, these tools exhibited high wear under the conditions of a 4-m cutting length and under the test conditions of a higher feed rate (125%), meaning that the original parameters were the most suited for machining with these tool types. It is shown that T1 was more sensitive to feed rate variations, whereas T2 was more sensitive to cutting length variations, in terms of flank wear.

#### 3.6.3. Wear Mechanism Analysis Summary

The wear mechanisms that were observed in the tools, mainly abrasice and adhesive wear, are expected when machining DSS alloys [46,47]. It is worthy to note that the tool type that suffered the least amount of adhesive wear was T1, since this tool only has two flutes. This enables a better chip evacuation, as the lubricant can cool and clean a larger area. However, in this tool there was evidence of abrasion, coating delamination and cracking, despite the AlCrN coating's structure. This is due to, once again, the tool having only two flutes. Thus, a four-fluted or plus design is preferred to machine this type of material.

T3 tools exhibited high amounts of adhesion when compared to the other tools, especially at higher cutting lengths. This led to the formation of a built-up edge. However, the flank wear that was registered for these tools was not very severe. The tools coated with TiAlSiN showed the best wear performance. Indeed, this coating is well known to perform well in terms of wear, even in the machining of hard materials [56]. Although these tools exhibited the same wear patterns as the other tools, these were not so severe in the flank. However, these tools suffered damage on their rake faces, due to the buildup of adhered material in this area. In Table 16, the summary of the wear analysis performed on all tested tools is presented, showing the main mechanisms registered for these.


**Table 16.** Summary of the SEM wear analysis for each of the tested tools, mentioning the main wear type and mechanism identified.
