3.5.3. T3—Wear Mechanism Analysis

Regarding the wear mechanisms sustained by T3 tools, these exhibited high levels of material adhesion to the tools' surfaces, especially at high feed rates, and even originated a built-up edge. This can be observed in Figure 14.

**Figure 14.** Built-up edge detected on the clearance face of a T3 tool, tested at 125% feed rate.

Other wear mechanisms were identified, being the same as the reported in the previously mentioned tools. There was evidence of abrasive wear and coating delamination, as seen in Figure 15. This delamination was promoted by the high amount of material adhesion and abrasion of the workpiece material on the tool's surface. The material adhesion promoted abrasive wear on these adhesion zones, eventually resulting in the spalling of the tool's coating (through adhesive wear).

**Figure 15.** Material adhesion and abrasive wear detected on a T3 tool's rake face, tested at 125% feed rate.

Unlike in T1 and T2 tools, no major cracks were registered; however, some cracks in the nanometric scale were identified. These "nanocracks" can eventually lead to bigger ones, resulting in coating spalling and delamination. The propagation of these cracks is known to be slowed down by multi-layered coatings, such as the T3 coating in use [16,17]. This can be observed in Figure 16.

**Figure 16.** Cracks, detected in the coating of a T3 tool, tested at 75% feed rate and 4 m of cutting length.

As seen from figures presented in this subsection, this tool exhibited high amounts of adhesion and abrasion, exposing the substrate in some areas. There was, however, a low amount of flank wear reported, and this tool produced satisfactory results in terms of machined surface quality. Comparing this tool to T1, coated with the same AlCrN coating, it can be concluded that there is a clear benefit in using a tool with four flutes to machine these types of DSS alloys.
