[Back]

A Kirnbauer, C.M. Koller, S. Koloszvári, P.H. Mayrhofer:
"Structure, mechanical properties and thermal stability of reactively sputtered AlTaTiVZr high-entropy nitride coatings";
Talk: 16th International Conference on Plasma Surface Engineering, Garmisch; 2018-09-17.

In the field of materials research, a novel alloying concept, so-called high-entropy alloys (HEAs), has gained particular attention within the last decade. These alloys contain 5 or more elements in equiatomic or near-equiatomic composition. Properties, like hardness, strength, and toughness can be attributed to the specific elemental distribution and are often superior to those of conventional alloys. In parallel to HEAs also high-entropy ceramics (HECs) moved into in the focus of research. These consist of a solid solution of 5 or more binary nitrides, carbides, oxides, or borides. Within this work, we investigate the structure and, mechanical properties of thin films based on the high-entropy materials concept, with emphasis on the thermal stability. According to the Gibbs free energy, the thermal stability should be improved in the high temperature regime.
Therefore, AlTaTiVZr nitride coatings were reactively sputtered in a lab-scale sputter deposition facility using a single powder-metallurgically produced composite target. The coatings in as-deposited state show a columnar growth and crystallise in a single-phase face-centred cubic structure. The hardness of our coatings is with 32.8±1.1 GPa in the range of TiN and TiAlN prepared with comparable growth parameters. The structural evolution of free-standing powdered coating material upon annealing was investigated by DSC and X-ray diffraction, showing only marginal structural changes between 900 and 1200 °C which indicates a stabilisation due to the high-entropy effect. Upon annealing up to 1500 °C there is a slight indication of a second phase emerging from the dominant fcc-structured matrix. Up to an annealing temperature of 1100 °C the hardness values of around 30 GPa are maintained. Annealing above 1100 °C, leads to thermally-induced grain growth and partial decomposition causing a decrease of the hardness.

high-entropy alloys (HEA), thermal stability, reactive sputter deposition