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| Editors: | F. Kongoli, I. Chung, H. Kageyama, M.G. Kanatzidis, F. Marquis, A. Navrotsky, A. Tressaud, J. Atwood, G. Duca, R. Kuroda, A. Legocki, J. Lipkowski, M. Zaworotko, R. Singh, R. Gupta, M. Halama, D. Macdonald, F. Wang |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2025 |
| Pages: | 262 pages |
| ISBN: | 978-1-998384-62-4 (CD) |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
Titanium alloys are widely used as aerospace structural materials because of their low density, high strength and excellent corrosion resistance at low-to-moderate temperatures. However, when the working temperature is over 400°C, titanium alloys usually show a poor oxidation resistance because of the fast diffusion of oxygen through the nascent TiO2–X surface oxide layer[1]. On the other hand, SiO2 shows considerable promise as a protective oxide layer, for both high temperature oxidation corrosion; however, the most successful application so far of Si–based oxides to Ti–alloys is the preprocessed amorphous (or ‘enamel’) SiO2 coating [2]. Ti–based Multi-Principal Element Alloys with added Si potentially provide a novel opportunity to find new alloy compositions which could form an SiO2–based layer spontaneously at elevated temperatures [3]. Boron has also been suggested as a further alloying addition, that could avoid the possible issue of pesting of formed silicide compounds in such MPEAs at intermediate temperatures [4].
This research builds an equimolar TiCrAlNb MPEA alloy system with different ratios of Si and/or B content and characterizes their microstructure, before and after oxidation, to study the influence of the addition of silicon and boron. The oxidation resistance of such alloys shows in general a significant improvement compared with a typical Ti-6Al-4V Ti–alloy. Furthermore, Niobium shows a higher tendency to form compounds with silicon/boron. In addition to such silicide/boride compounds, some laves phases were also observed and the addition of silicon showed a significant influence on the microstructure, the addition of B refines the lamellar microstructure while the addition of Si transfers the structure into an equiaxed dendritic structure.