1 College of Energy and Power Engineering, Changsha University of Science and Technology, Changsha 410076, China 2 School of Mechanical and Energy Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, China 3 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
LV Yunlei, REN Yanjie, FENG Kangkang, ZHOU Mengni, WANG Wen, CHEN Jian, NIU Yan. High Temperature Oxidation Mode and Transformation Mechanism of Quaternary Co-Ni-Cr-Al Alloys. Acta Metall Sin, 2024, 60(7): 947-956.
The addition of Ni to cobalt-based alloys can form the γ′ phase, which can significantly improve their mechanical properties and high-temperature oxidation resistance. The oxidation behavior of quaternary Co-20Ni-8Cr-xAl (x = 3 or 5, mass fraction, %) alloys was investigated in 1.013 × 105 Pa O2 at 800, 900, 1000, and 1100oC. Also, the effects of Al and/or Cr contents and temperature on the oxidation properties of the alloys were explored by analyzing the oxidation kinetics of the alloys and the cross-sectional morphology characteristics of the scales, revealing the oxidation mechanism of these alloys. After oxidation, both the alloys formed complex scales with irregular thickness and composition. Alumina scales were generated for each alloy at 800, 900, and 1000oC and only for Co-20Ni-8Cr-5Al at 1100oC. The increase in temperature from 800oC to 900oC has a negative effect on the oxidation resistance, resulting in greatly accelerated oxidation rates. Conversely, that from 1000oC to 1100oC has a positive effect on the oxidation of the two alloys, causing a decrease in the oxidation rate. The oxidation rate of the Co-Ni-Cr-Al alloy decreases when the Al content in the alloy is increased from 3% to 5%, but 5% is still not sufficient to form continuous alumina scales. The simultaneous presence of Cr and Al is beneficial to reducing the oxidation rate of the quaternary Co-Ni-Cr-Al alloys compared with the ternary Co-Ni-Al alloy with the same Al content.
Fund: National Natural Science Foundation of China(52171066);National Natural Science Foundation of China(51771034);Natural Science Foundation of Hunan Province(2020JJ4610);Postgraduate Scientific Research Innovation Project of Hunan Province(CX20200871)
Corresponding Authors:
REN Yanjie, professor, Tel: 13657310308, E-mail: yjren@csust.edu.cn;
Table 1 Nominal and actual compositions of Co-20Ni-8Cr-3Al and Co-20Ni-8Cr-5Al alloys
Fig.1 Kinetic curves for the oxidation of the Co-20Ni-8Cr-3Al and Co-20Ni-8Cr-5Al alloys in 1.013 × 105 Pa O2 at 800oC (a, b), 900oC (c, d), 1000oC (e, f), and 1100oC (g, h) for 20 h (t—time; kp, kp1, and kp2—rate constants) (a, c, e, g) linear plots (b, d, f, h) parabolic plots
Fig.2 Kinetic curves for oxidation of the Co-20Ni-8Cr-3Al (a) and Co-20Ni-8Cr-5Al (b) alloys in 1.013 × 105 Pa O2 at 800, 900, 1000, and 1100oC for 20 h
Fig.3 Cross-sectional morphologies (a, b) and element distributions (c) of Co-20Ni-8Cr-3Al alloy oxidized in 1.013 × 105 Pa O2 at 800oC for 24 h (Fig.3b is the enlarged view of selected area in Fig.3a; IOZ—internal oxidation zone)
Fig.4 Cross-sectional morphologies of Co-20Ni-8Cr-3Al alloy oxidized in 1.013 × 105 Pa O2 at 900oC for 24 h (a) general view (b) view of a different region
Fig.5 Cross-sectional morphologies of Co-20Ni-8Cr-3Al alloy oxidized in 1.013 × 105 Pa O2 at 1000oC (a1, a2) and 1100oC (b1, b2) for 20 h (Figs.5a2 and b2 are the enlarged views of selected areas in Fig.5a1 and b1, respectively)
Fig.6 Cross-sectional morphologies of Co-20Ni-8Cr-5Al alloy oxidized in 1.013 × 105 Pa O2 at 800oC (a1, a2) and 900oC (b1, b2) for 24 h (Figs.6a2 and b2 are the enlarged views of selected areas in Figs.6a1 and b1, respectively)
Fig.7 Cross-sectional morphologies of Co-20Ni-8Cr-5Al alloy oxidized in 1.013 × 105 Pa O2 at 1000oC (a1, a2) and 1100oC (b1, b2) for 20 h (Figs.7a2 and b2 are the enlarged views of selected areas in Figs.7a1 and b1, respectively)
Fig.8 XRD spectra of Co-20Ni-8Cr-3Al (a) and Co-20Ni-8Cr-5Al (b) alloys oxidized in 1.013 × 105 Pa O2 at 800 and 900oC for 24 h
Fig.9 XRD spectra of Co-20Ni-8Cr-3Al (a) and Co-20Ni-8Cr-5Al (b) alloys oxidized in 1.013 × 105 Pa O2 at 1000 and 1100oC for 20 h
Type of scale
Oxidation product
I
MO (thick), Al2O3, Cr2O3, spinel
II
MO (thin), Al2O3, Cr2O3, spinel
III
Al2O3, Cr2O3, spinel
IV
Al2O3
Table 2 Oxidation products of four scale types on Co-20Ni-8Cr-3Al and Co-20Ni-8Cr-5Al alloys
Temperature / oC
Co-20Ni-8Cr-3Al
Co-20Ni-8Cr-5Al
800
Type II + type IV
Type II + type IV
900
Type II
Type II
1000
Type II
Type II
1100
Type II
Type II + type IV
Table 3 Classification of the scales grown on the Co-20Ni-8Cr-3Al and Co-20Ni-8Cr-5Al alloys at 800, 900, 1000, and 1100oC
Fig.10 Comparisons of the kinetic curves for the oxi-dation in 1.013 × 105 Pa O2 at 800oC (a), 900oC (b), and 1000oC (c) for 20 h of the quaternary Co-20Ni-8Cr-xAl alloys with the corresponding data for the ternary Co-20Ni-xAl[31] alloys
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