2.2.1. Sample Preparation

To characterize the tool-coating thickness and the sustained tool wear after machining, the tools were subject to a preparation procedure. The mentioned analyses were performed using SEM (FEI QUANTA 400 FEG, Field Electron and Ion Company, FEI, Hillsboro, OR, USA). Regarding the tool coating analysis, firstly, an unused tool was cut (cross-section) in a coated area using a STRUERS MINITOM (Struers, Inc., Cleveland, OH, USA) disc saw equipped with a thin disc with electroplated diamond particles in its cutting area. After cutting, the sample was mounted in thermoset resin and placed in a STRUERS PEDOPRESS hot press (Struers, Inc., Cleveland, OH, USA). This mounting step was performed to enable the sample's preparation for SEM analysis. This preparation consisted of subjecting the mounted sample to grinding and polishing processes using silicon carbide (SiC) sandpaper with different grits in the following sequence: 220, 550, 800, and 1200 grit. After the grinding process, the sample was rotated 90◦ to reduce undesirable abrasion marks. Following the grinding process, the samples were subject to a polishing stage using two types of diamond slurry, one with an average particle size of 3 μm and another with an average particle size of 1 μm. Each polishing step was performed for about 15 min to reduce the abrasion marks on the samples' surfaces. A total of three samples for coating analysis were produced in this manner.

The tools used in the machining tests were additionally prepared to enable the sustained wear analysis, also using SEM. After machining, the tools were cut using the same STRUERS MINITOM (Struers, Inc., Cleveland, OH, USA) disc saw equipment, this time cutting the tools in an uncoated area. All the tools were cut in the same area, guaranteeing that all samples had the same length; moreover, during the cutting of the samples, the protection of the cutting area was ensured, preventing possible damage that would negatively impact the subsequent analysis of the tool wear and wear mechanisms. This cutting

procedure enabled a more detailed analysis of the top of the tools in the SEM equipment. After cutting, all of the tools were subject to a cleaning procedure, more specifically, an ultrasonic bath using acetone for 5 min.
