Structural Study of Nanostructured Multilayer CrAlN Coatings Prepared by Physical Vapor Deposition

In this paper, nanostructured CrAlN coatings were deposited onto steel substrates using an industrial cathodic arc physical vapor deposition (Arc-PVD) technique. Field emission scanning electron microscopy (FESEM) was employed to evaluate the microstructure and the phase analysis was carried out using Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) methods. The XRD patterns were used to determine the crystallographic texture of the coatings and the results showed (222) as the dominant texture. Moreover, it was found that all coatings had nanocrystalline structure with crystallite sizes between 8-18 nm. CrN was found to be the dominant phase in the XRD patterns; addition of aluminum produced CrAlN, leading to shifts of the diffraction peaks. Cr2N and AlN phases were identified by the XRD pattern which can be attributed to the decrease of the nitrogen pressure down below a critical value and the increase in the evaporation of aluminium, respectively. The change in the Al content of the coating and the subsequent displacement of the diffraction lines caused a challenge in the phase identification procedure. Therefore, identifying the existing phases in the coating was not feasible merely by the EXPERT software since CrAlN is not defined in its database; the crystal phase data of the nitride coatings must be used for accurate phase identification.