Investigation on Optimal Ta/Cr Ratio of a Single Crystal Ni-Base Superalloy in View of the Isothermal Oxidation Behavior
The relative content of strengthening element tantalum (Ta) and oxidation-resistant element chromium (Cr) is an essential value for superalloys to obtain an excellent combination of oxidation resistance and mechanical properties. In the present paper, the isothermal oxidation behavior of several sin...
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| Autores principales: | , , , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/9de8ee6e4bd447eb9006be35292cd922 |
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| Sumario: | The relative content of strengthening element tantalum (Ta) and oxidation-resistant element chromium (Cr) is an essential value for superalloys to obtain an excellent combination of oxidation resistance and mechanical properties. In the present paper, the isothermal oxidation behavior of several single crystal Ni-base superalloys with different Ta/Cr (wt. %, similarly hereinafter) ratios at 1000 °C in static air has been systematically investigated to explore the optimal Ta/Cr for excellent oxidation resistance. A detailed microstructure study using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and an electro-probe microanalyzer (EPMA) was performed to reveal the oxidation products and mechanisms. For all alloys, a three-layer structured scale consisting of an outer (Cr, Al, Ti, Ni, Ta)-O layer, an inner Al<sub>2</sub>O<sub>3</sub> layer and an inner nitride layer was formed. As Ta/Cr increased, the amounts of Ta-containing products, cracks, holes and inner nitride increased. Meanwhile, the completeness of the Al<sub>2</sub>O<sub>3</sub> layer got worse. It was shown that if Ta/Cr ≤ 0.5, Ta increased the growth rate of Cr<sub>2</sub>O<sub>3</sub> via the doping effect induced by Ta cations. If Ta/Cr > 0.5, Ta reduced the completeness of Cr<sub>2</sub>O<sub>3</sub> through competitive growth of Ta<sub>2</sub>O<sub>5</sub> and Cr<sub>2</sub>O<sub>3</sub>. A good oxidation performance can be expected with the value Ta/Cr ≤ 0.5. |
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