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ICMCTF - 2013
Corinna Sabitzer (C. Sabitzer)
"Architectural design of Al-rich cubic coating materials within the AlN-CrN system "
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Aluminum chromium nitride (AlxCr1-xN) coatings (within the AlN-CrN quasibinary system) are known for their excellent oxidation and wear resistance, thermal stability and high hardness. In general, these properties are correlated to their Al content, x. Recent studies indicated that by increasing x up to ~ 0.75 (hence, 75 at% Al of the metal sublattice), which corresponds to the ab initio suggested solubility limit within the cubic (NaCl type) structure, the film properties can be enhanced significantly. Exceeding this Al content, a cubic/hexagonal or a single phase hexagonal (wurtzite ZnS type) structure will be formed, resulting in decreased properties. However, stabilizing Al-rich AlxCr1-xN coatings in a single phase cubic structure should result in a further increase in mechanical properties and thermal behavior. Therefore, monolithic as well as multilayered AlxCr1-xN coatings were deposited by cathodic arc evaporation (in N2 atmosphere) using powder metallurgically prepared AlxCr1-x targets with compositions of x = 0.7, 0.75, 0.85, and 0.9. X-ray diffraction studies clearly exhibit a single phase cubic structure for the monolithically grown nitride coatings using Al0.7Cr0.3 and Al075Cr0.25 targets, a mixed cubic/hexagonal structure for the coatings prepared from Al0.85Cr0.15 targets, and a single phase hexagonal structure when using Al0.9Cr0.1 targets, independent from the dc bias voltage applied to the substrates. Multilayer variations of the single phase cubic layers with the mixed cubic/hexagonal or hexagonal layers (by combining the individual targets during the preparation by an industrial plant) contain also a hexagonal phase fraction in addition to the cubic phases when applying low bias voltages of -40 V. However, when increasing the bias voltage up to -120 V, the hexagonal phase formation can be suppressed. This is even valid for the multilayer arrangements combining Al0.75Cr0.25N layers with the highest Al containing layers prepared from Al0.9Cr0.1 targets. These multilayers (Al0.75Cr0.25N/Al0.9Cr0.1N) exhibit a pronounced hexagonal phase content when applying -40 V bias but a cubic structure for -120 V bias. The structural modification from pronounced hexagonal to cubic results in increased hardness values, from ~17 to 32 GPa, as well as increased thermal stability and oxidation resistance.
Our results highlight the importance of an architectural design in addition to the alloy development for optimized material properties and performance.

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