Experimental and DFT Investigations of AlNbTiVZr High Entropy Alloys with Excellent Mechanical Properties

doi:10.1007/s40195-024-01716-x

Abstract

Abstract:

This study investigated the microstructure and mechanical properties of AlNbTiVZr series high-entropy alloys (HEAs) through both experimental studies and density functional theory calculations. Significant improvements in the microstructures and mechanical properties were achieved for the AlNbTiVZr series HEAs by meticulously adjusting the alloy composition and employing homogenization heat treatment. Notably, the specimen designated as Al_0.5NbTiVZr_0.5 demonstrated excellent mechanical properties including a compressive yield strength of 1162 MPa and a compressive strength of 1783 MPa. After homogenization heat treatment at 1000 °C for 24 h, the Al_0.5NbTiVZr_0.5 alloy exhibits brittle-to-ductile transition. Further atomic-scale theoretical simulations reveal that the decrease of Al content intrinsically enhances the ductility of the alloys, thereby indicating that the mechanical properties of the AlNbTiVZr series HEAs were significantly influenced by the chemical composition. Additionally, specific atomic pair formations were observed to adversely affect the microstructure of the AlNbTiVZr series HEAs, particularly in terms of ductility. These findings provide valuable insights for the design and optimization of light weight HEAs, emphasizing the synergistic adjustment of alloy composition and heat treatment processes to achieve a balance between the strength and ductility.

Key words: High-entropy alloy, Microstructure, Mechanical properties, Density functional theory

Hongwei Yan, Yong’an Zhang, Wei Xiao, Boyu Xue, Rui Liu, Xiwu Li, Zhihui Li, Baiqing Xiong. Experimental and DFT Investigations of AlNbTiVZr High Entropy Alloys with Excellent Mechanical Properties[J]. Acta Metallurgica Sinica (English Letters), 2024, 37(9): 1480-1490.

Figures/Tables 11

Table 1 Compositions of the alloys (at.%)

Alloys		Al	Ti	V	Zr	Nb
AlNbTiVZr	Nominal	20	20	20	20	20
	800 °C	19	25	16	18	22
	1000 °C	20	20	20	20	20
Al_0.5Nb TiVZr_0.5	Nominal	12.5	25	25	12.5	25
	800 °C	12	29	28	12	19
	1000 °C	12	25	25	13	25

Fig. 1 Crystal models of Al26Nb26Ti26V26Zr24

Fig. 2 SEM images of the microstructure of the as-cast and annealed HEAs specimens. a1 as-cast Al-Zr; a2 Al-Zr annealing of 800 °C/24 h; a3 Al-Zr of annealing 1000 °C/24 h; b1 as-cast Al0.5-Zr0.5 b2 Al0.5-Zr0.5 annealing of 800 °C/24 h, b3 Al0.5-Zr0.5 annealing of 1000 °C/24 h

Fig. 3 Element distribution in the two HEAs after annealing: a1 Al-Zr at 800 °C; a2 Al-Zr at 1000 °C; b1 Al0.5-Zr0.5 at 800 °C; b2 Al0.5-Zr0.5 at 1000 °C

Fig. 4 a Engineering compression stress-strain curves, b relevant mechanical properties

Table 2 Atomic radius, Pauling electronegativity, VEC, density, crystal structure, and ground state energy per atom for alloying elements [12,36]

	Atomic No	Atomic radius (Å)	Pauling electronegativity	VEC	ρ (g·cm⁻³)	Crystal structure (RT)	$E_{i}^{{{\text{bulk}}}}$(eV·atom⁻¹)
Al	13	1.43	1.61	3	2.7	FCC	−3.75
Ti	22	1.46; 1.47	1.54	4	4.51	HCP	−7.76
V	23	1.32; 1.34	1.63	5	6.00; 6.11	BCC	−8.94
Zr	40	1.6	1.55; 1.33	4	6.51; 6.52	HCP	−8.52
Nb	41	1.43; 1.46	1.6	5	8.57	BCC	−10.21

Table 3 Calculated lattice constant, VEC, formation energy, and elastic constants of different HEAs

Alloys	Source	α (nm)	VEC	E_form (eV·atom⁻¹)	C₁₁	C₁₂	C₄₄	B	E	G	v	B/G
AlNbTiVZr	Al₂₆Nb₂₆Ti₂₆V₂₆Zr₂₄ (SQS)	0.326 0.325[37] 0.326^[22]	4.20	−0.04	150.3	108.3	40.0	122.3	85.5	30.9	0.393	3.96
	Al₂₆Nb₂₆Ti₂₆V₂₆Zr₂₄ (MC)	0.326	4.20	−0.10	158.5	106.8	46.1	124.0	99.9	36.6	0.366	3.39
Al_0.5NbTiVZr_0.5	Al₁₆Nb₃₂Ti₃₂V₃₂Zr₁₆ (SQS)	0.324	4.38	0.00	150.7	116.3	34.6	127.7	73.4	26.2	0.404	4.88

Fig. 5 Comparison of the bond order and bond number for the Al26Nb26Ti26V26Zr24 and Al16Nb32Ti32V32Zr16 structures

Fig. 6 Calculated density of states (DOS) of Al26Nb26Ti26V26Zr24 with both a SQS, b MC structures. The Fermi energies are set to 0 eV, marked by vertical dashed lines

Fig. 7 $\alpha_{{{{ij}}}}^{v}$ of different pairs for the first nearest-neighbor shell of the SQS and MC structures of Al26Nb26Ti26V26Zr24

Fig. 8 Comparison of the bond order and bond number of the SQS and MC structures of Al26Nb26Ti26V26Zr24

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