XPS spectra of CC620 at 250 m/min are presented in Figure 11. An adequate amount of alumina(Al2O3) tribo-film with sapphire crystal structure was found (HR Al2s spectrum, binding energyof 117 eV). This tribo-film acts as a thermal barrier at elevated cutting temperatures prevents heatpenetration to the tool surface and subsurface that can cause the tool damage; moreover, this tribo-filmformation reduces the adhesive wear effect [20]. ZrO2 tribo-film was detected in Figure 11 (HR Zr3dspectrum, binding energy of 183.3 eV). Its formation decreases the coefficient of friction at the tool-chipinterface [37]. The detection of these tribo-films supported the results obtained from the wear curveat 250 m/min in Figure 3, chip compression ratio presented in Figure 9, and the chip undersidemicrographs illustrated in Figure 11. When the cutting speed reaches 700 m/min, ZrO2 tribo-filmbecomes ineffective due to the expected increase of the cutting temperature to more than 900 ◦C.This was shown by the wear curve in Figure 5.J. Manuf. Mater. Process. 2018, 2, x FOR PEER REVIEW 10 of 14penetration to the tool surface and subsurface that can cause the tool damage; moreover, this tribofilm formation reduces the adhesive wear effect [20]. ZrO2 tribo-film was detected in Figure 11 (HRZr3d spectrum, binding energy of 183.3 eV). Its formation decreases the coefficient of friction at thetool-chip interface [37]. The detection of these tribo-films supported the results obtained from thewear curve at 250 m/min in Figure 3, chip compression ratio presented in Figure 9, and the chipunderside micrographs illustrated in Figure 11. When the cutting speed reaches 700 m/min, ZrO2tribo-film becomes ineffective due to the expected increase of the cutting temperature to more than900 °C. This was shown by the wear curve in Figure