Microstructure, Mechanical and Corrosion Properties of AlCoCrFeNi High-Entropy Alloy Prepared by Spark Plasma Sintering

doi:10.1007/s40195-019-00962-8

Abstract

Abstract:

AlCoCrFeNi is one of the most widely studied alloy systems in the high-entropy alloy (HEA) area due to the interesting microstructure and mechanical properties. In this study, the AlCoCrFeNi alloy was prepared using spark plasma sintering (SPS) with pre-alloy powders obtained through gas atomization. Then, the sintered samples were annealed at 700, 800 and 900 °C, and the effect of annealing temperature on the microstructure, mechanical and corrosion properties was studied. The results show that phase formation takes place during annealing process with the new phase (σ) and some nanoscale BCC precipitates formation. The size and quantity of the nanoscale precipitates increase with increasing annealing temperature. The twin is also observed after annealing at 900 °C. The annealing temperature has an obvious effect on the mechanical properties and corrosion resistance of the spark plasma sintered AlCoCrFeNi HEA. When the annealing temperature is 700 °C, the hardness, yield strength and fracture strength reach the maximum with the value of 545 HV, 1430 MPa and 2230 MPa, respectively. The compressive ratio reaches the maximum of 17.2%, with the annealing temperature increasing to 800 °C. The corrosion resistance of the samples decreases with increasing the annealing temperature.

Key words: High-entropy alloy, Phase transformation, Precipitates, Mechanical property, Corrosion resistance

P. F. Zhou, D. H. Xiao, T. C. Yuan. Microstructure, Mechanical and Corrosion Properties of AlCoCrFeNi High-Entropy Alloy Prepared by Spark Plasma Sintering[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(7): 937-946.

Figures/Tables 13

Fig. 1 XRD patterns of the spark plasma sintered and annealed samples a, and the enlarged region of two theta ranging between 43° and 45.5° b

Fig. 2 Microstructures of a Sample 1, b Sample 2, c Sample 3, d Sample 4

Table 1 Chemical compositions (at%) of phases in the spark plasma sintered sample

Regions	Phase	Al	Cr	Fe	Co	Ni
Light gray	FCC	8.7	14.59	33.28	26.67	16.76
Dark gray	BCC	0.58	85.84	8.93	3.47	1.18
Gray	B2	26.58	6.45	19.04	22.19	25.74

Fig. 3 High-magnification microstructures of a Sample 2, b Sample 3, c Sample 4 annealed at different temperatures

Table 2 Chemical compositions (at%) of phases in the annealed samples

Regions	Phase	Al	Cr	Fe	Co	Ni
Precipitates (1)	BCC	22.97	17.57	18.29	19.16	22.01
Light gray (2)	FCC	4.92	25.89	31.77	24.10	13.42
Gray (3)	B2	27.58	11.42	15.71	19.53	25.76
White gray (4)	σ	5.87	43.56	25.06	18.88	6.61

Fig. 4 EPMA mapping images of a Sample 1 and b Sample 4

Fig. 5 TEM bright-field images and the corresponding selected area electron diffraction patterns of a Sample 1, b and c Sample 4

Fig. 6 Room-temperature compressive stress-strain curves of the samples

Table 3 Mechanical properties of the samples

Sample	Hardness (HV)	σ_0.2 (MPa)	σ_f (MPa)	ε_f (%)
Sample 1	497 ± 13	1390 ± 15	2150 ± 17	12.1 ± 0.3
Sample 2	545 ± 8	1430 ± 18	2230 ± 14	13.3 ± 0.2
Sample 3	544 ± 9	1350 ± 16	2195 ± 18	17.2 ± 0.3
Sample 4	458 ± 12	1120 ± 14	2090 ± 15	15.0 ± 0.4

Fig. 7 Compressed fractographic feature of a Sample 1, b Sample 2, c Sample 3, d Sample 4

Fig. 8 Polarization curves of the samples

Table 4 Dynamic parameters derived from the potentiodynamic polarization curves by linear fitting

Sample	E_corr (V vs. SCE)	I_corr (μA/cm²)	R_p(Ω)
Sample 1	- 0.463	17.8	1388.8
Sample 2	- 0.445	19.2	1246.8
Sample 3	- 0.363	89.1	629.3
Sample 4	- 0.315	108.0	401.2

Fig. 9 Dissolution morphologies of the four samples after the polarization tests: a Sample 1, b Sample 2, c Sample 3, d Sample 4

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