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T. Glechner, O Hudak, T. Wojcik, L. Haager, F. Bohrn, H. Hutter, O Hunold, J. Ramm, S. Kolozsvári, E. Pitthan, D. Primetzhofer, H. Riedl:
"Influence of the non-metal species on the oxidation kinetics of Hf, HfN, HfC, and HfB2 coatings";
Materials & Design, 211 (2021), 110136; 1 - 12.

The influence of the non-metal species on the oxidation resistance of transition metal ceramic based thin films is still unclear. For this purpose, we thoroughly investigated the oxide scale formation of a metal (Hf), carbide (HfC0.96), nitride (HfN1.5), and boride (HfB2.3) coating grown by physical vapor deposition. The non-metal species decisively affect the onset temperature of oxidation, ranging between 550 °C for HfC0.96 to 840 °C for HfN1.5. HfB2.3 and HfN1.5 obtain the slowest oxide scale kinetic following a parabolic law with kp values of 4.97∙10-10 and 5.66∙10-11 kg2 m-4 s−1 at 840 °C, respectively. A characteristic feature for the oxide scale on Hf coatings, is a columnar morphology and a substantial oxygen inward diffusion. HfC0.96 reveals an ineffective oxycarbide based scale, whereas HfN1.5 features a scale with globular HfO2 grains. HfB2.3 exhibits a layered scale with a porous boron rich region on top, followed by a highly dense and crystalline HfO2 beneath. Furthermore, HfB2.3 presents a hardness of 47.7 ± 2.7 GPa next to an exceptional low inward diffusion of oxygen during oxidation. This study showcases the strong influence of the non-metallic bonding partner despite the same metallic basis, as well as the huge potential for HfB2 based coatings also for oxidative environments.

Thin films; Borides; Oxide-film growth kinetics; Oxidation; Hafnium

http://dx.doi.org/10.1016/j.matdes.2021.110136

https://publik.tuwien.ac.at/files/publik_298087.pdf

Project Head Helmut Riedl:
CDL-SEC