Structural optimisation and synthesis of multilayers and nanocomposite AlCrTiSiN coatings for excellent machinability

In the present work, based on AlCrN coatings, AlTiSiN and AlCrTiSiN multilayer and nanocomposite coatings were designed and deposited on high-speed steel (HSS) specimens and cutters by cathodic vacuum arc process. The microstructures of these coatings were investigated by grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and high-resolution transmission electron microscope (HRTEM), in association with mechanical property characterisation, and also with a cutting test used to check the service life of coated tools. The results showed that the AlTiSiN coating was composed of nanocrystalline TiN and hcp-AlN. The AlCrTiSiN multilayers and nanocomposite coating contained (111), (200), and (220) planes of TiN and CrN with a face-centred cubic structure (fcc) and nanocrystalline fcc-(Cr,Al)N phases. The AlCrTiSiN coating had a stronger diffraction (200) peak compared with the AlTiSiN coating. Those coatings were superlattice with nanocomposite structures containing nanocrystalline and amorphous phases. The modulation period (7 nm) of the AlCrTiSiN coating was much smaller than the 12 nm of AlTiSiN. A special Cr2N particulate phase existed in the AlCrTiSiN coating. The service life of an AlCrTiSiN coated tool increased by approximately 50% when compared with that with an AlCrN coating because of its excellent mechanical properties (41.14 GPa hardness, 1.07 GPa toughness, 60 N LC2 adhesion strength, 0.2 average friction coefficient, and 36.5 nm (Ra) roughness).