Structural investigations of aluminum-chromium-nitride hard coatings by Raman micro-spectroscopy

Abstract Arc-evaporated aluminum-chromium-nitride (AlxCr1−xN) hard coatings were characterized using Raman micro-spectroscopy. The main Raman bands were assigned to vibrational modes. Changes in Raman intensities were attributed to incorporation of aluminum in the CrN structure and possibly to resonance enhancement. Raman shifts decreased with the Al-content caused by lattice contractions and compressive stress in the coatings. Transition from phases with dominating cubic to dominating hexagonal structure at x > 0.71 was indicated by downshift of all modes and changes in relative intensity ratios. Increased intensity of the transversal acoustic mode at 633 nm excitation was potentially caused by resonance enhancement. Phase content and structure were found to be substrate independent down to 0.5 μm below the coating surface. Increasing bias voltages during coating deposition resulted in considerable high residual stress up to several GPa. No preferential orientation of coating crystallites was found in substrate parallel planes.