Thermodynamic and microstructural study of Ti2AlNb oxides at 800 °C

J M Xiang; G B Mi; S J Qu; X Huang; Z Chen; A H Feng; J Shen; D L Chen

doi:10.1038/s41598-018-31196-w

Thermodynamic and microstructural study of Ti₂AlNb oxides at 800 °C

Sci Rep. 2018 Aug 24;8(1):12761. doi: 10.1038/s41598-018-31196-w.

Authors

J M Xiang¹, G B Mi², S J Qu³, X Huang², Z Chen^{1

4}, A H Feng¹, J Shen¹, D L Chen⁵

Affiliations

¹ School of Materials Science and Engineering, Tongji University, Shanghai, 201804, P.R. China.
² Aviation Key Laboratory of Science and Technology on Advanced Titanium Alloys, AECC Beijing Institute of Aeronautical Materials, Beijing, 100095, China.
³ School of Materials Science and Engineering, Tongji University, Shanghai, 201804, P.R. China. qushoujiang@tongji.edu.cn.
⁴ Aerospace Hiwing (Harbin) Titanium Industrial Co., Ltd., Harbin, 150028, China.
⁵ Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Ontario, M5B 2K3, Canada. dchen@ryerson.ca.

Abstract

The high-temperature structural applications of Ti₂AlNb-based alloys, such as in jet engines and gas turbines, inevitably require oxidation resistance. The objective of this study is to seek fundamental insight into the oxidation behavior of a Ti₂AlNb-based alloy via detailed microstructural characterization of oxide scale and scale/substrate interface after oxidation at 800 °C using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). The oxide scale exhibits a complex multi-layered structure consisting of (Al,Nb)-rich mixed oxide layer (I)/mixed oxide layer (II)/oxygen-rich layer (III)/substrate from the outside to inside, where the substrate is mainly composed of B2 and O-Ti₂AlNb phases. High-resolution TEM examinations along with high-angle annular dark-field (HAADF) imaging reveal: (1) the co-existence of two types (α and δ) of Al₂O₃ oxides in the outer scale, (2) the presence of metastable oxide products of TiO and Nb₂O₅, (3) an amorphous region near the scale/substrate interface including the formation of AlNb₂, and (4) O-Ti₂AlNb phase oxidized to form Nb₂O₅, TiO₂ and Al₂O₃.