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ICMCTF - 2014
Robert Hollerweger (R. Hollerweger)
"Structure and Mechanical Properties of Ta alloyed Cr-Al-N coatings"
R. Hollerweger, L. Zhou, D. Holec, R. Rachbauer, P. Polcik, P. H. Mayrhofer
Transition metal alloying of Cr1-xAlxN based coatings is commonly used to improve their mechanical properties and thermal stability. Recent reports show that Tantalum additions to Ti1-xAlxN type coatings positively influence their properties, but only little information is available on the effect of Ta on Cr1-xAlxN based coatings. Consequently, we have performed a combined experimental and ab initio based study on the influence of Ta additions (0, 2, 6, 12, and 26 at% on the metal sublattice) on structure and mechanical properties of arc evaporated Cr1-x-yAlxTayN coatings with Al/(Cr+Al) ratios > 0.61. With increasing Ta-content the droplet number density decreases and coating surface smoothens, which is much more pronounced as with increasing the bias voltage from 40 to 120 V. Simultaneously, the columnar structure observed for Ta-free Cr0.37Al0.63N significantly changes into a fine grained structure (crystallite size ~5 nm) with clearly reduced columnar character. Additionally,
increasing the Ta content favors the formation of a preferred 200 growth orientation resulting in a reduction of the indentation moduli from ~500 to ~375 GPa, which is in agreement with ab initio calculations. As the hardness of our coatings remains at ~35 GPa with increasing Ta content, this indicates an increase in fracture toughness at still high resistance against plastic deformation.

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