On the Microstructure and Properties of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn (at.%) Silicide-Based Alloy—RM(Nb)IC
The microstructure, isothermal oxidation, and hardness of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn alloy and the hardness and Young’s moduli of elasticity of its Nb<sub>ss</sub> and Nb<sub>5</sub>Si<sub>3</sub> were studied. The alloy was selected using the niobium inte...
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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/c60cbb42f22a42ad8496e367a8fa7502 |
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| Sumario: | The microstructure, isothermal oxidation, and hardness of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn alloy and the hardness and Young’s moduli of elasticity of its Nb<sub>ss</sub> and Nb<sub>5</sub>Si<sub>3</sub> were studied. The alloy was selected using the niobium intermetallic composite elaboration (NICE) alloy design methodology. There was macrosegregation of Ti and Si in the cast alloy. The Nb<sub>ss</sub>, αNb<sub>5</sub>Si<sub>3</sub>, γNb<sub>5</sub>Si<sub>3</sub>, and HfO<sub>2</sub> phases were present in the as-cast or heat-treated alloy plus TiN in the near-the-surface areas of the latter. The vol.% of Nb<sub>ss</sub> was about 80%. There were Ti- and Ti-and-Hf-rich areas in the solid solution and the 5-3 silicide, respectively, and there was a lamellar microstructure of these two phases. The V partitioned to the Nb<sub>ss</sub>, where the solubilities of Al, Cr, Hf, and V increased with increasing Ti concentration. At 700, 800, and 900 °C, the alloy did not suffer from catastrophic pest oxidation; it followed parabolic oxidation kinetics in the former two temperatures and linear oxidation kinetics in the latter, where its mass change was the lowest compared with other Sn-containing alloys. An Sn-rich layer formed in the interface between the scale and the substrate, which consisted of the Nb<sub>3</sub>Sn and Nb<sub>6</sub>Sn<sub>5</sub> compounds at 900 °C. The latter compound was not contaminated with oxygen. Both the Nb<sub>ss</sub> and Nb<sub>5</sub>Si<sub>3</sub> were contaminated with oxygen, with the former contaminated more severely than the latter. The bulk of the alloy was also contaminated with oxygen. The alloying of the Nb<sub>ss</sub> with Sn increased its elastic modulus compared with Sn-free solid solutions. The hardness of the alloy, its Nb<sub>ss</sub>, and its specific room temperature strength compared favourably with many refractory metal-complex-concentrated alloys (RCCAs). The agreement of the predictions of NICE with the experimental results was satisfactory. |
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