Micro-Raman Spectroscopic Study of the Tribology of AlCrN Coated Cemented Tungsten Carbide Pins Dry Sliding on Hardened Steel Discs

Metal nitride and binary metal nitride coatings have been widely applied to cemented tungsten carbide (WC) cutting tools to enhance tool life and productivity in machining applications. In this study we report the use of micro-Raman spectroscopy to understand the tribological behavior of one such coating, namely, AlCrN coated cemented WC pins dry sliding on hardened steel (HCHCR) discs. The tribo-testing parameters were chosen based on a correspondence with the cutting force and the cutting speed on a specific machining application. Well-resolved lattice vibrations, arising from the acoustic and optical phonon bands of the crystalline AlCrN coatings, are clearly discernable in the Raman spectra measured on pristine pins. These characteristic signals are utilized to assess the changes occurring in the coatings after tribological experiments. Spatially-resolved, micro-Raman spectra measured on tribo-tested pins suggest that predominantly the AlCrN coatings are intact under the tribological conditions tested here, except for a small region in the middle of the wear scar where the coating appears to have worn off. These spectra also reveal that wear debris composed of iron oxides particles adhered to the pin surface during the tribological testing. Time evolution of the microscopic wear and the adhered oxide layer, were further studied by acquiring Raman spectra through stop-start tribo-tests at different intervals of time. These spectra apart from revealing the evolution of microscopic wear of the coating, also reveal the transitory nature of the iron oxides deposited during the tribo-tests. Deposits of Fe 2 O 3 that are initially adhered to the pin surface appear to transform possibly into Fe 3 O 4 over a period of time. These spectral observations are discussed in light of the tribological data.