Abstract

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.

Highlights

  • Surface protection of highly stressed components used in aviation and energy industries is a highly relevant topic with respect to sustainable development and extending the longevity of high-end machine elements

  • Whereas a lot of studies have been done on oxidation resistant Ultra High Temperature Ceramics (UHTC) boride and carbide based bulk ceramics [6,7,8], the development of protective physical vapor deposition (PVD) coatings has mainly focused on TMnitrides, (TiN, Ti1-xAxlN, CrN [9])

  • The adaptation of the non-metallic bonding partner – in particular nitrogen – to enhance the oxidation resistance, was not into the focus as nitrogen does not interact with oxygen and gets released during oxidation

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Summary

Introduction

Surface protection of highly stressed components used in aviation and energy industries is a highly relevant topic with respect to sustainable development and extending the longevity of high-end machine elements. HfC0.96, HfN1.5 and HfB2.3 coatings exhibit different oxide scale morphologies. 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.

Results
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