2.1.1. Machining Tools

The employed tools are end-mills (INOVATOOLS, S.A., Leiria, Portugal) their substrate is a cemented carbide WC-Co, grade 6110. The substrate presents an average grain size of about 0.3 μm and uses 6% Co (percentual mass fraction) as a binder. Figure 1a depicts the tools' shape.

The tools' substrates (INOVATOOLS, S.A., Leiria, Portugal) were supplied with the tools' final dimensions and geometry, as they were commercial tools sold by the supplier. However, these tools were then coated with a coating developed in the laboratory. The tools were coated with a TiN/TiAlN multilayer coating. After the machining of the tools' substrates, they were subjected to a cleaning operation and then coated. The tool coating was obtained using PVD CemeCom CC800/HiPIMS equipment (CemeCon, Wuerselen, Germany) with four target holders. The adopted deposition parameters can be observed in Table 1.


**Table 1.** Deposition parameters for the TiN/TiAlN tool coatings.

Coating deposition started with the opening of the shutters of the two pure titanium targets, enabling the deposition of the first thin layer of TiN onto the tools' substrates. After this initial deposition, these shutters closed and the ones for the TiAl targets opened, thus enabling the deposition of the outer TiAlN layer, which was thicker than the former. These deposition parameters were selected based on previously conducted experiments on similar substrates. After coating deposition, the tools were carefully packed, avoiding the handling of the cutting area.

#### 2.1.2. Workpiece Material

The selected workpiece material (Paris Saint Denis Aero Portugal, Grândola, Portugal) was an austenitic nickel–chromium-based superalloy, Inconel 718. The workpiece material was supplied as a round bar, having a 158 mm diameter. Regarding heat treatments, the material underwent a solution annealing process at 970 ◦C, followed by rapid cooling by water quenching. Then, it underwent precipitation hardening at 718 ◦C for 8 h before being cooled in a furnace until 621 ◦C. This temperature was maintained for 8 h, with the material then being removed from the furnace and left to cool in air. The material's mechanical properties are presented in Table 2, and its respective chemical composition (%wt) is shown in Table 3.

**Table 2.** Workpiece material's (Inconel 718) mechanical properties determined at room temperature.


**Table 3.** Workpiece material's (Inconel 718) chemical composition (%wt).


In addition to the elements considered in Table 3, residual elements, such as Ag, Ca, Pb, Bi, S, and O, were present; however. only trace amounts were found; thus, they were not considered relevant to include in Table 3.
