Thermal Deformation Behavior of Al19.3Co15Cr15Ni50.7 High Entropy Alloy
LIU Qingqi, LU Ye, ZHANG Yifei, FAN Xiaofeng, LI Rui, LIU Xingshuo, TONG Xue, YU Pengfei, LI Gong()
State Key Laboratory of Metastable Materials Preparation Technology and Science, Yanshan University, Qinhuangdao 066004, China
Cite this article:
LIU Qingqi, LU Ye, ZHANG Yifei, FAN Xiaofeng, LI Rui, LIU Xingshuo, TONG Xue, YU Pengfei, LI Gong. Thermal Deformation Behavior of Al19.3Co15Cr15Ni50.7 High Entropy Alloy. Acta Metall Sin, 2021, 57(10): 1299-1308.
Al19.3Co15Cr15Ni50.7 is a eutectic high entropy alloy with a lamellar structure and good high-temperature properties. To study the thermal deformation behavior of the samples (diameter 8 mm, height 10 mm), the samples were hot compressed using the Gleeble-3500 thermal simulation-testing machine. The true stress-true strain curves were obtained for strain rates between 0.001 and 0.1 s-1 and deformation temperatures from 973 K to 1273 K. According to the Arrhenius model, the constitutive equation of the alloy in the strain range of 0.1-0.7 is established, and the deformation activation energy and material parameters under different strain conditions were obtained. With the strain (ε) as the independent variable, the material constants are fitted using the sixth order polynomial, such that the material constant of a certain strain, and the constitutive equation of the strain is obtained. Finally, the constitutive equation is verified. Based on the power dissipation theory and instability criterion of the dynamic material model, the power dissipation and instability diagram are constructed, and the hot working diagram in the strain range of 0.3-0.7 for the Al19.3Co15Cr15Ni50.7 high entropy alloy is established by the superposition of the two diagrams. The results show that the flow stress curve at 1273 K presents dynamic recovery characteristics, while the flow stress curve at other temperatures presents dynamic recrystallization characteristics, and the flow stress increases with a decrease in the deformation temperature or an increase in the strain rate. The constitutive equation was established and verified, and the decision coefficient R2 = 0.956, which was relatively high, indicates that the established flow stress constitutive model could predict the flow stress of the alloy. After high-temperature compression, compared with the as-cast microstructure, the strip-shaped B2 phase has some bending after hot deformation, and even fracture may occur under the condition of a high-strain rate. The original fine lamellar B2 phase grows into coarse lamellar, and based on the dynamic material model (DMM) theory, the stable zone and unstable zone are determined, and the optimal process parameters are determined.
Fig.1 XRD spectrum of Al19.3Co15Cr15Ni50.7 high entropy alloy (HEA)
Fig.2 BSE-SEM image of as-cast Al19.3Co15Cr15Ni50.7 HEA
Fig.3 True stress-true strain curves under the deformation conditions of = 0.001 s-1 (a), = 0.01 s-1 (b), and = 0.1 s-1 (c) (—strain rate)
s-1
973 K
1073 K
1173 K
1273 K
0.001
676.4
282.5
126.1
49.3
0.01
882.2
466.9
208.3
98.8
0.1
1110.0
717.8
338.9
149.6
Table 1 Stress (σ) of Al19.3Co15Cr15Ni50.3 HFA at the strain ε = 0.3 and different deformation temperatures
Fig.4 The relationship curves of σ and ln
Fig.5 The relationship curves of lnσ and ln
Fig.6 The relationship curves of ln and ln[sinh(ασ)] (α is the stress level parameter )
Fig.7 The relationship curves of ln[sinh(ασ)] and 1/T (T—temperature)
Fig.8 The relationship curve of lnZ andln[sinh(ασ)] (Z—Zener-Hollmon parameter)
ε
α / MPa-1
n
lnA
Q / (kJ·mol-1)
0.1
0.00280
6.03
49.95
523.71
0.2
0.00304
4.13
39.82
427.14
0.3
0.00385
3.22
38.77
421.36
0.4
0.00479
2.92
42.66
462.11
0.5
0.00570
2.89
47.03
506.32
0.6
0.00620
3.11
47.52
511.17
0.7
0.00635
3.44
49.05
525.03
Table 2 Al19.3Co15Cr15Ni50.7 parameters of high entropy alloy at different strains
i
Ai
Bi
Ci
Di
1
A1 = -509.81
B1 = -0.0717
C1 = -17.3
D1 = 12272.3
2
A2 = 2703.96
B2 = 0.5683
C2 = -122.2
D2 = -110146.9
3
A3 = -9151.22
B3 = -2.1461
C3 = 847.1
D3 = 440190.3
4
A4 = 20543.76
B4 = 4.4862
C4 = -2054.7
D4 = -868593.3
5
A5 = -25122.01
B5 = -4.8284
C5 = 2289.6
D5 = -832663.5
6
A6 = 12140.51
B6 = 2.0617
C6 = -977.3
D6 = -310120.4
7
A7 = -509.81
B7 = -0.0718
C7 = -17.3
D7 = 12272.3
Table 3 Polynomial fitting parameters of the sixth degree in Eq.(12)
Fig.9 The curves of α (a), n (b), lnA (c), and Q (d) with strain
Fig.10 Comparisons of experimental value (curve) and calculated values (symbol) of flow stress under different deformation conditions of 0.001 s-1 (a), 0.01 s-1 (b), and 0.1 s-1 (c)
Fig.11 Comparison of calculated and experimental values of flow stress
Fig.12 BSE-SEM images of Al19.3Co15Cr15Ni50.7 hot deformed sample at 1173 K
Fig.13 Heat working diagrams under different variable conditions (The numbers in the figures are the values of dissipation rate, the shadows represent instable zones)
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