Long-Term Oxidation Behavior and Microstructural Evolution of γ-TiAl Alloys at 700 oC in Air

doi:10.11900/0412.1961.2023.00443

Acta Metall Sin

2025, Vol. 61

Issue (8): 1217-1228 DOI: 10.11900/0412.1961.2023.00443

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Long-Term Oxidation Behavior and Microstructural Evolution of γ-TiAl Alloys at 700 ^oC in Air

ZHOU Zhichun¹^,², LIU Renci¹(

), ZHANG Jianda¹^,³, YANG Chao⁴, CUI Yuyou¹, YANG Rui¹

^1.Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
^2.School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
^3.School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, China
^4.AECC Commercial Aero-Engine Co. Ltd., Shanghai 200241, China

Cite this article:

ZHOU Zhichun, LIU Renci, ZHANG Jianda, YANG Chao, CUI Yuyou, YANG Rui. Long-Term Oxidation Behavior and Microstructural Evolution of γ-TiAl Alloys at 700 ^oC in Air. Acta Metall Sin, 2025, 61(8): 1217-1228.

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Abstract

γ-TiAl alloys are a new generation of high-temperature lightweight materials characterized by low density, high specific modulus of elasticity, excellent high-temperature strength, and creep resistance, making them highly suitable for aviation, aerospace, and automotive engine applications. A typical application of the alloys is in the low-pressure turbine blades of aero-engines, such as GEnx and Trent XWB developed by the General Electric and Rolls-Royce, respectively. Their alloy compositions are Ti-48Al-2Cr-2Nb and Ti-45Al-2Nb-2Mn-1B (atomic fraction, %), respectively. γ-TiAl alloys are required for long-term service at 600-700 ^oC; however, they react readily with oxygen to form oxide scale when exposed in air at high temperatures, compromising service safety and reliability. Thus, understanding the long-term oxidation behavior of γ-TiAl alloys during service at high temperatures is imperative. In this study, the oxide scale and microstructural evolution of cast Ti-45Al-2Nb-2Mn-1B alloy (45XD alloy) and Ti-48Al-2Nb-2Cr alloy (4822 alloy) at 700 ^oC in air for 0-2000 h were investigated using SEM and TEM. The mass gain of both alloys was measured during oxidation, and their oxidation behaviors were compared. The 4822 alloy exhibited a notably higher mass gain than the 45XD alloy. Both alloys demonstrated periodic mass gain behavior during oxidation for 0-2000 h—alternating rapid and slow gains—with stabilization in the later stages. The oxide scales formed layered structures, primarily of TiO₂ and Al₂O₃, on the surface of both alloys; the scale of 45XD alloy was continuous and dense, whereas that of the 4822 alloy was porous. Additionally, the study revealed that α₂ lamellae in the subsurface of the 45XD alloy decomposed during oxidation, forming an Al-rich and Ti-lean γ zone on the subsurface. α₂ lamellae in the bulk microstructure of the 45XD alloy were also decomposed and transformed into γ phase. The 4822 alloy experienced a significant reduction in the volume fractions of α₂ in equiaxed γ grains and α₂ + β₀ at equiaxed γ grain boundaries.

Key words: γ-TiAl alloy isothermal oxidation mass gain layered oxide scale microstructural stability

Received: 13 November 2023

ZTFLH:

TG146.2

Fund: Major Special Science and Technology Project of Yunnan Province(202302AB080009);CAS Project for Young Scientists in Basic Research(YSBR-025);National Key Research and Development Program of China(2021YFB3702605);National Science and Technology Major Projects of China(J2019-VII-0002-0142)

Corresponding Authors: LIU Renci, professor, Tel: (024)83970951, E-mail: rcliu@imr.ac.cn

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	ZHOU Zhichun
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	CUI Yuyou
	YANG Rui

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https://www.ams.org.cn/EN/10.11900/0412.1961.2023.00443 OR https://www.ams.org.cn/EN/Y2025/V61/I8/1217

Fig.1 OM images of the initial microstructures of 45XD (a) and 4822 (b) alloys

Fig.2 Isothermal oxidation kinetics curves (a) and oxide scale thicknesses (b) of 45XD and 4822 alloys at 700 ^oC in air

Table 1 Stages of oxidation kinetics curves and average mass gain rates of 45XD and 4822 alloys

Fig.3 XRD spectra of surfaces of 45XD (a) and 4822 (b) alloy specimens after oxidation at 700 ^oC in air for different time

Fig.4 Surface morphologies of 45XD (a, b) and 4822 (c, d) alloy specimens after oxidation at 700 ^oC in air for 200 h (a, c) and 500 h (b, d)

Table 2 Chemical composition of oxides on the surface of 45XD and 4822 alloy specimens

Fig.5 Cross-sectional SEM-BSE images of 45XD (a-c) and 4822 (d-f) alloy specimens after oxidation at 700 ^oC in air for 200 h (a, d), 500 h (b, e), and 2000 h (c, f) (Insets in Figs.5a and e are corresponding locally enlarged views)

Fig.6 Bright-field (BF) TEM images (a, d), dark-field (DF) TEM image (b), and the selected area electron diffraction (SAED) pattern from the circular area in Fig.6a (c) of (α₂ + γ) lamellar colonies in the bulk of 45XD alloy specimens after oxidation at 700 ^oC for 0 h (a-c) and 2000 h (d) (Fig.6b shows α₂ lamellae in Fig.6a)

Fig.7 SEM-BSE (a, c) and BF TEM (b, d) images of the bulk of 4822 specimens after oxidation at 700 ^oC for 0 h (a, b) and 2000 h (c, d) (Inset in Fig.7b shows the SAED pattern of the circular area)

Fig.8 Microstructures and elemental distributions of 45XD alloy specimens after oxidation at 700 ^oC in air for 200 h (a), 500 h (b), and 2000 h (c)

Fig.9 Microstructures and elemental distributions of 4822 alloy specimens after oxidation at 700 ^oC in air for 200 h (a), 500 h (b), and 2000 h (c)

Fig.10 Schematics of the oxide scale formation as well as subsurface microstructural evolution of 45XD alloy (a-d) and 4822 alloy (e-h) during oxidation at 700 ^oC in air for 0 h (a, e), 200 h (b, f), 500 h (c, g), and 2000 h (d, h)

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