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.
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 CrNbTiVAl0.75 to 323.33 MPa·cm3/g in CrNbTiVAl0.25. 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.
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) Al0.25 (b) Al0.5 (c) Al0.75 (d) Al1.0
Alloy
Region
Cr
Nb
Ti
V
Al
Al0.25
Nominal
23.53
23.53
23.53
23.53
5.88
bcc
27.32
27.24
10.55
29.00
5.89
Laves
30.97
25.19
11.33
25.96
6.54
α-Ti
00.23
05.40
90.29
03.96
0.12
Al0.50
Nominal
22.22
22.22
22.22
22.22
11.12
bcc
33.29
22.58
16.14
18.76
09.23
Laves
33.41
23.64
14.50
19.62
08.84
α-Ti
00.45
04.67
90.96
03.48
00.13
Al0.75
Nominal
21.05
21.05
21.05
21.05
15.80
bcc
21.22
22.99
17.40
23.48
14.91
Laves
30.44
20.28
16.65
22.02
10.62
α-Ti
00.45
05.39
89.30
04.53
00.34
Al1.0
Nominal
20
20
20
20
20
bcc
20.52
19.62
19.84
20.08
19.06
Laves
31.27
18.33
17.63
20.38
12.39
α-Ti
00.11
03.46
93.10
03.04
00.29
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
Alloy
σ0.2
MPa
σf
MPa
εf
%
ρ
g·cm-3
SYS
MPa·cm3·g-1
Al0.25
2037
2131
12.35
6.30
323.33
Al0.5
1917
2012
14.50
6.09
314.78
Al0.75
1274
1314
06.16
5.90
215.93
Al1.0
1371
1398
06.65
5.73
239.27
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
Alloy
t / h
kp1 / (mg2·cm-4·s-1)
R2
t / h
kp2 / (mg2·cm-4·s-1)
R2
Al0.25
0-40
1.98 × 10-1
0.94
40-100
2.90 × 10-2
0.97
Al0.5
0-40
1.43 × 10-1
0.96
40-100
5.31 × 10-2
0.97
Al0.75
0-40
8.81 × 10-2
0.93
40-100
7.23 × 10-2
0.98
Al1.0
0-40
5.71 ×10-2
0.94
40-100
8.91 × 10-2
0.99
Table 3 Parabolic rate constants (kp1, kp2) 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) Al0.25 (b, f) Al0.5 (c, g) Al0.75 (d, h) Al1.0
Alloy
Spot
Identified phase
Cr
Nb
Ti
V
Al
O
Al0.25
1
(CrNbTiVAl)O2
10.05
11.37
10.13
04.38
02.28
61.79
2
VO x
03.61
03.09
04.71
16.38
01.27
70.94
3
Al2O3
04.05
00.58
00.37
01.25
33.61
60.14
Al0.5
4
(CrNbTiVAl)O2
09.15
9.60
11.35
03.64
03.12
63.14
5
Al2O3
04.35
0.06
00.43
00.23
34.98
59.95
Al0.75
6
VO x
03.35
2.87
04.08
15.50
01.39
72.81
7
(CrNbTiVAl)O2
07.33
8.94
09.84
03.16
04.53
66.20
8
Al2O3
03.39
0.61
00.95
01.85
36.02
57.18
Al1.0
9
(CrNbTiVAl)O2
15.11
15.22
16.96
03.45
02.63
46.63
10
Al2O3
03.65
00.00
00.07
00.62
33.31
62.35
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) Al0.25 (b) Al0.5 (c) Al0.75 (d) Al1.0
Alloy
ΔHmix / (kJ·mol-1)
ΔSmix / (J·K-1·mol-1)
Ω
δ / %
VEC
ΔχA / %
Al0.25
0-7.86
12.71
3.52
5.94
4.88
7.16
Al0.5
-10.67
13.15
2.60
5.81
4.77
7.13
Al0.75
-12.85
13.33
2.12
5.69
4.69
7.08
Al1.0
-14.56
13.38
1.83
5.57
4.60
7.03
Table 5 Calculated thermodynamic parameters in the CrNbTiVAl x RHEAs
Fig.9 Standard Gibbs free energy (ΔGθ) 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
1
Yeh J W, Chen S K, Lin S J, et al. Nanostructured high-entropy alloys with multiple principal elements: Novel alloy design concepts and outcomes[J]. Adv. Eng. Mater., 2004, 6: 299
2
Lu Y P, Dong Y, Guo S, et al. A promising new class of high-temperature alloys: Eutectic high-entropy alloys[J]. Sci. Rep., 2014, 4: 6200
doi: 10.1038/srep06200
pmid: 25160691
3
Miracle D B, Senkov O N. A critical review of high entropy alloys and related concepts[J]. Acta Mater., 2017, 122: 448
4
Maresca F, Curtin W A. Mechanistic origin of high strength in refractory BCC high entropy alloys up to 1900 K[J]. Acta Mater., 2020, 182: 235
5
Lu Y P, Dong Y, Jiang H, et al. Promising properties and future trend of eutectic high entropy alloys[J]. Scr. Mater., 2020, 187: 202
6
Miao J W, Wang M L, Zhang A J, et al. Tribological properties and wear mechanism of AlCr1.3TiNi2 Eutectic high-entropy alloy at elevated temperature[J]. Acta Metall. Sin., 2023, 59: 267
Zhang Y, Zuo T T, Tang Z, et al. Microstructures and properties of high-entropy alloys[J]. Prog. Mater. Sci., 2014, 61: 1
8
Liu N, Ding W, Wang X J, et al. Microstructure evolution and phase formation of Fe25Ni25Co x Mo y multi-principal-component alloys[J]. Metall. Mater. Trans., 2020, 51A: 2990
9
Jia Y H, Wang Z J, Wu Q F, et al. Boron microalloying for high-temperature eutectic high-entropy alloys[J]. Acta Mater., 2024, 262: 119427
10
Pei X H, Du Y, Wang H M, et al. Investigation of high temperature tribological performance of TiZrV0.5Nb0.5 refractory high-entropy alloy optimized by Si microalloying[J]. Tribol. Int., 2022, 176: 107885
11
Senkov O N, Wilks G B, Miracle D B, et al. Refractory high-entropy alloys[J]. Intermetallics, 2010, 18: 1758
12
Senkov O N, Wilks G B, Scott J M, et al. Mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys[J]. Intermetallics, 2011, 19: 698
13
Xu C R, Fang L Y, Xu G L, et al. Mechanical properties and oxidation behavior of NbMoTaW x refractory high entropy alloys[J]. J. Alloys Compd., 2024, 990: 174390
14
Senkov O N, Senkova S V, Woodward C, et al. Low-density, refractory multi-principal element alloys of the Cr-Nb-Ti-V-Zr system: Microstructure and phase analysis[J]. Acta Mater., 2013, 61: 1545
15
Senkov O N, Miracle D B, Chaput K J, et al. Development and exploration of refractory high entropy alloys—A review[J]. J. Mater. Res., 2018, 33: 3092
16
Stepanov N D, Yurchenko N Y, Skibin D V, et al. Structure and mechanical properties of the AlCr x NbTiV (x = 0, 0.5, 1, 1.5) high entropy alloys[J]. J. Alloys Compd., 2015, 652: 266
17
Senkov O N, Senkova S V, Miracle D B, et al. Mechanical properties of low-density, refractory multi-principal element alloys of the Cr-Nb-Ti-V-Zr system[J]. Mater. Sci. Eng., 2013, A565: 51
18
Butler T M, Chaput K J, Dietrich J R, et al. High temperature oxidation behaviors of equimolar NbTiZrV and NbTiZrCr refractory complex concentrated alloys (RCCAs)[J]. J. Alloys Compd., 2017, 729: 1004
19
Yurchenko NY, Stepanov N D, Zherebtsov S V, et al. Structure and mechanical properties of B2 ordered refractory AlNbTiVZr x (x = 0-1.5) high-entropy alloys[J]. Mater. Sci. Eng., 2017, A704: 82
20
Zhu M, Yao L J, Liu Y Q, et al. Microstructure evolution and mechanical properties of a novel CrNbTiZrAl x (0.25 ≤ x ≤ 1.25) eutectic refractory high-entropy alloy[J]. Mater. Lett., 2020, 272: 127869
21
Qiao D X, Liang H, Wu S Y, et al. The mechanical and oxidation properties of novel B2-ordered Ti2ZrHf0.5VNb0.5Al x refractory high-entropy alloys[J]. Mater. Charact., 2021, 178: 111287
22
Dong Z Q, Sun A K, Yang S, et al. Machine learning-assisted discovery of Cr, Al-containing high-entropy alloys for high oxidation resistance[J]. Corros. Sci., 2023, 220: 111222
23
Anber E A, Beaudry D, Brandenburg C, et al. Oxidation resistance of Al-containing refractory high-entropy alloys[J]. Scr. Mater., 2024, 244: 115997
24
Lu S D, Li X X, Liang X Y, et al. Effect of Al content on the oxidation behavior of refractory high-entropy alloy AlMo0.5NbTa0.5TiZr at elevated temperatures[J]. Int. J. Refract. Met. Hard Mater., 2022, 105: 105812
25
Zhang Y Y, Wu H B, Yu X P, et al. Role of Cr in the high-temperature oxidation behavior of Cr x MnFeNi high-entropy alloys at 800 oC in air[J]. Corros. Sci., 2022, 200: 110211
26
Li Z, Wang L, Wang B B, et al. Oxidation behavior of Ti-Nb-Mo-Al-Si x refractory high entropy alloy at 1000 oC[J]. Corros. Sci., 2022, 206: 110504
27
Guo Y L, Peng J, Peng S Y, et al. Improving oxidation resistance of TaMoZrTiAl refractory high entropy alloys via Nb and Si alloying[J]. Corros. Sci., 2023, 223: 111455
28
Chang C H, Titus M S, Yeh J W. Oxidation behavior between 700 and 1300 oC of refractory TiZrNbHfTa high-entropy alloys containing aluminum[J]. Adv. Eng. Mater., 2018, 20: 1700948
29
Stepanov N D, Yurchenko N Y, Shaysultanov D G, et al. Effect of Al on structure and mechanical properties of Al x NbTiVZr (x = 0, 0.5, 1, 1.5) high entropy alloys[J]. Mater. Sci. Technol., 2015, 31: 1184
30
Liu X W, Bai Z C, Ding X F, et al. A novel light-weight refractory high-entropy alloy with high specific strength and intrinsic deformability[J]. Mater. Lett., 2021, 287: 129255
31
Jiang W T, Wang X H, Li S Y, et al. A lightweight Al0.8Nb0.5Ti2V2Zr0.5 refractory high entropy alloy with high specific yield strength[J]. Mater. Lett., 2022, 328: 133144
32
Senkov O N, Senkova S V, Woodward C. Effect of aluminum on the microstructure and properties of two refractory high-entropy alloys[J]. Acta Mater., 2014, 68: 214
33
Wagner C. Beitrag zur theorie des anlaufvorgangs[J]. Z. Phys. Chem., 1933, 21B: 25
34
Liu C M, Wang H M, Zhang S Q, et al. Microstructure and oxidation behavior of new refractory high entropy alloys[J]. J. Alloys Compd., 2014, 583: 162
35
Guo S, Ng C, Lu J, et al. Effect of valence electron concentration on stability of fcc or bcc phase in high entropy alloys[J]. J. Appl. Phys., 2011, 109: 103505
36
Yurchenko N, Stepanov N, Salishchev G. Laves-phase formation criterion for high-entropy alloys[J]. Mater. Sci. Technol., 2017, 33: 17
