dc.description.abstract
In the field of materials research, a novel alloying concept, so-called high-entropy metal-sublattice ceramics have gained a lot of interest in the last years. These consist of a solid solution of 5 or more binary ceramics leading to a high-entropy metal-sublattice. Previous investigated material systems based on this concept have shown to be promising candidates for industrial applications due to their high thermal stability and good mechanical properties [1,2] Within this work, we investigate the structure, mechanical properties, and thermal stability of thin films based on (Al,Ta,Ti,V,Zr) with different Al contents.
For coating synthesis, we used a single powder-metallurgically produced composite target and additional Al cubes placed along the racetrack to increase the Al content within the coatings. The coatings were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as nanoindentation. Furthermore, vacuum annealing treatments were carried out to gain information about the thermal stability and the change of mechanical properties upon heat treatment.
The coatings in as-deposited state exhibit a fine-columnar growth morphology. X-ray diffraction (XRD) analysis shows that the coatings independent of the Al-content crystallise in a single-phase face-centred cubic (fcc) structure. The hardness and the indentation modulus of the investigated coatings in as-deposited state is ~31 GPa and 400 GPa, respectively, and are as well independent on the Al-content. We studied the influence of the Al content on the thermal stability by investigating the structural evolution of our coatings by XRD, as well as nanoindentation. Furthermore, also powdered coating material was investigated by XRD after heat treatment up to 1500 °C. All the coatings keep their hardness up to an annealing temperature of 1000°C. After annealing at higher temperatures, the precipitation w-AlN causes a decrease of the hardness. Furthermore, the XRDs of powdered coating material reveal a distinct influence of the Al-content on the decomposition of the solid solution into an fcc-matrix, a nitrogen depleted hexagonal phase, and Al-rich domains.
[1] A. Kirnbauer, A. Kretschmer, C.M. Koller, T. Wojcik, V. Paneta, M. Hans, J.M. Schneider, P. Polcik, P.H. Mayrhofer, Mechanical properties and thermal stability of reactively sputtered multi-principal-metal Hf-Ta-Ti-V-Zr nitrides, Surf. Coatings Technol. 389 (2020) 125674. https://doi.org/10.1016/j.surfcoat.2020.125674.
[2] A. Kirnbauer, A. Wagner, V. Moraes, D. Primetzhofer, M. Hans, J.M. Schneider, P. Polcik, P.H. Mayrhofer, Thermal stability and mechanical properties of sputtered (Hf,Ta,V,W,Zr)-diborides, Acta Mater. 200 (2020) 559–569. https://doi.org/10.1016/j.actamat.2020.09.018.
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