Influence of bias potential and layer arrangement on structure and mechanical properties of arc evaporated Al-Cr-N 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 Al0.7Cr0.25 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 Al0.5Cr0.25 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. (C) 2014 Elsevier Ltd. All rights reserved.