Microstructure, Mechanical Properties, and High-Temperature Oxidation Behaviors of the CrNbTiVAl x Refractory High-Entropy Alloys

doi:10.11900/0412.1961.2024.00201

Acta Metall Sin

2025, Vol. 61

Issue (1): 88-98 DOI: 10.11900/0412.1961.2024.00201

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Microstructure, Mechanical Properties, and High-Temperature Oxidation Behaviors of the CrNbTiVAl _x Refractory High-Entropy Alloys

ZHU Man(

), ZHANG Cheng, XU Junfeng, JIAN Zengyun, XI Zengzhe

School of Materials Science and Chemical Engineering, Xi'an Technological University, Xi'an 710021, China

Cite this article:

ZHU Man, ZHANG Cheng, XU Junfeng, JIAN Zengyun, XI Zengzhe. Microstructure, Mechanical Properties, and High-Temperature Oxidation Behaviors of the CrNbTiVAl _x Refractory High-Entropy Alloys. Acta Metall Sin, 2025, 61(1): 88-98.

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Abstract

Owing to their high thermal stability, good high-temperature mechanical properties, and excellent high-temperature oxidation resistance, refractory high-entropy alloys (RHEAs) are strong candidates for structural materials in high-temperature applications. To reduce the density and improve the high-temperature oxidation resistance of RHEAs, in this study, the Al element was added into CrNbTiV alloys, forming a series of CrNbTiVAl _x RHEAs (x = 0.25, 0.5, 0.75, 1.0). The effects of Al content on the microstructure, mechanical properties, and high-temperature oxidation behaviors of the CrNbTiV RHEAs were studied using XRD, SEM, EDS, and an electronic universal testing machine. A mixture of bcc, Laves, and α-Ti phases was found in the CrNbTiVAl _x RHEAs and equiaxed grains were observed in the bcc phase. Increasing the Al content decreased the density of the alloys and reduced the yield strength from 2037 to 1371 MPa. The specific yield strength ranged from 215.93 MPa·cm³/g in CrNbTiVAl_0.75 to 323.33 MPa·cm³/g in CrNbTiVAl_0.25. After oxidation at 900 ^oC, the CrNbTiVAl _x RHEAs exhibited parabolic oxidation kinetics and their high-temperature oxidation resistance was improved due to increased Al content. The oxidized products were determined as Al₂O₃, (CrNbTiVAl)O₂, and VO _x. The surfaces of the alloys with low Al content formed a continuous and compact complex oxide (CrNbTiVAl)O₂ that effectively prevented the diffusion of O₂ into the substrate. Increasing the Al content decreased the amount of complex oxide (CrNbTiVAl)O₂, forming denser, continuous, and finer Al₂O₃ oxides on the surface that appreciably improved the high-temperature oxidation resistance.

Key words: refractory high-entropy alloy microstructure mechanical property high-temperature oxidation resistance

Received: 18 June 2024

ZTFLH:

TG113

Fund: National Natural Science Foundation of China(51971166);National Natural Science Foundation of China(51904218)

Corresponding Authors: ZHU Man, professor, Tel: (029)86173324, E-mail: zhuman0428@126.com

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	ZHU Man
	ZHANG Cheng
	XU Junfeng
	JIAN Zengyun
	XI Zengzhe

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https://www.ams.org.cn/EN/10.11900/0412.1961.2024.00201 OR https://www.ams.org.cn/EN/Y2025/V61/I1/88

Fig.1 XRD spectra (a) and enlarged view of the primary diffraction peak (b) of the CrNbTiVAl _x (x = 0.25, 0.5, 0.75, and 1.0, molar ratio) refractory high-entropy alloys (RHEAs)

Fig.2 Backscattered electron (BSE) images of microstructures of the CrNbTiVAl _x RHEAs
(a) Al_0.25 (b) Al_0.5 (c) Al_0.75 (d) Al_1.0

Table 1 EDS results in different regions of the CrNbTiVAl _x RHEAs

Fig.3 Compressive stress-strain curves of the CrNbTiVAl _x RHEAs tested at room temperature

Table 2 Compressive property, density, and specific yield strength of the CrNbTiVAl _x RHEAs

Fig.4 Comparison plots of SYS vs ρ for present CrNbTiVAl _x RHEAs and other HEAs reported in the literatures [12,16,17,20,29-32]

Fig.5 Oxidation kinetic curves of the CrNbTiVAl _x RHEAs oxidized at 900 ^oC
(a) mass gain per unit area (Δm / S) as a function of time (t)
(b) variation of (Δm / S)²vst

Table 3 Parabolic rate constants (k_p1, k_p2) of the CrNbTiVAl _x RHEAs after oxidation at 900 ^oC

Fig.6 XRD spectra of the CrNbTiVAl _x RHEAs after oxidation at 900 ^oC for 10 h (a) and 100 h (b)

Fig.7 Low (a-d) and high (e-h) magnified surface morphologies of the CrNbTiVAl _x RHEAs after oxidation at 900 ^oC for 100 h
(a, e) Al_0.25 (b, f) Al_0.5 (c, g) Al_0.75 (d, h) Al_1.0

Table 4 EDS results in different regions in Fig.7 of the CrNbTiVAl _x RHEAs after oxidation at 900 ^oC for 100 h

Fig.8 Cross-sectional morphologies and EDS mapping results of CrNbTiVAl _x RHEAs after oxidation at 900 ^oC for 10 h
(a) Al_0.25 (b) Al_0.5 (c) Al_0.75 (d) Al_1.0

Table 5 Calculated thermodynamic parameters in the CrNbTiVAl _x RHEAs

Fig.9 Standard Gibbs free energy (ΔG^θ) vs temperature (T) curves of oxides in the CrNbTiVAl _x alloys

Fig.10 Schematics showing the oxidation mechanism of CrNbTiVAl _x RHEAs at high temperatures
(a) pre-oxidation (b) early stages of oxidation(c) mid-oxidation(d) post-oxidation

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