Influence of bias potential and layer arrangement on structure and mechanical properties of arc evaporated Al–Cr–N coatings

• Impact of bias potential on monolithic and multilayered AlxCr1−xN coatings.
• Al0.85Cr0.15N can be stabilized in the cubic structure within a multilayer system.
• Monolithically grown Al0.7Cr0.3N and Al0.75Cr0.25N show hardness of ∼38 GPa.
• High hardness of ∼37 GPa is obtained for Al0.7Cr0.3N/Al0.85Cr0.15N coatings.

Monolithically grown as well as multilayered AlxCr1−xN coatings were deposited by cathodic arc evaporation using AlxCr1−x targets with compositions of x = 0.7, 0.75, 0.85, and 0.9. X-ray diffraction analysis revealed a single phase cubic structure for the monolithically grown nitride coatings using Al0.7Cr0.3 and Al0.75Cr0.25 targets. A mixed cubic/hexagonal structure is obtained when using Al0.85Cr0.15 targets, and a single phase hexagonal structure when using Al0.9Cr0.1 targets. Multilayer variations, combining single phase cubic layers (using Al0.7Cr0.3 and Al0.75Cr0.25 targets) with the mixed cubic/hexagonal (using Al0.85Cr0.15 targets) or hexagonal layers (using Al0.9Cr0.1 targets) show also hexagonal phase fractions in addition to the cubic phases when applying low bias potentials of −40 V. However, increasing the bias potential supports the coherency strains to suppress the growth of the less dense hexagonal phase. Therefore, even for a high overall Al/Cr ratio of 77/23 at% hardness values around 33 GPa are obtained.