Influence of alloying elements on mechanical and electronic properties of NbMoTaWX (X = Cr, Zr, V, Hf and Re) refractory high entropy alloys
Introduction
High entropy alloys (HEAs), firstly reported by Yeh et al., are a kind of novel structure materials breaking through the conventional alloy design concept [[1], [2], [3]]. Composed of five to thirteen elements with equiatomic or near equiatomic content, HEAs are inclined to form single-phase solid solution structure, such as face-centered cubic (FCC), body-centered cubic (BCC) or close-packed hexagonal (HCP) [[4], [5], [6]]. Generally, HEAs are considered to have high entropy effects, lattice distortion effect, slow diffusion effect and cocktail effect [7,8]. They own excellent mechanical properties and have great application prospects. Particularly, refractory high entropy alloys (RHEAs), composed of refractory elements, such as Nb, Ta, Mo, W, have high temperature resistance and outstanding high temperature strength [[9], [10], [11], [12]]. They are considered to be new high temperature alloys for higher temperature applications that exceeding the serving temperature of Ni-based high-temperature alloys. For instance, the firstly reported RHEAs, Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 [13,14], possess BCC single-phase solid solution structure, and have high temperature stability up to 1600 °C. Importantly, their yield strength maintains 405 MPa and 477 MPa up to 1600 °C. It should be noted that the mechanical strength of Nb25Mo25Ta25W25 alloy was significantly improved after adding alloying element V, demonstrating that alloying enhancement is an effective method to strengthen RHEAs as it works in the traditional alloys. Though Nb25Mo25Ta25W25 RHEA has excellent high temperature performance, its ductility is quite poor at room temperature, which hinders the alloy's engineering application. Some investigations have been done to improve the ductility and strength of Nb25Mo25Ta25W25 RHEAs by alloying with V, Ti, Re and Cu [[13], [14], [15], [16], [17], [18], [19]]. For example, the yield strength of NbMoTaW RHEA at room temperature was improved from 1058 MPa to 1246 MPa by V alloying while it still maintained the low fracture strain [14]. Ti alloying obviously enhanced both the strength (from 1058 MPa to 1343 MPa) and ductility (from 2.6% to 14.1%) of NbMoTaW RHEA [15]. It is confirmed that different alloying elements have different strengthening effect on the NbMoTaW RHEA. Some elements merely strengthen the alloy without any improvement of ductility while others enhance both the strength and ductility. However, the effect of alloying element on this alloy's mechanical properties, such as strength and ductility, is still unclear up to now, and needs systematic investigations. In present work, elements with high melting points over 1850 °C, such as Cr, Zr, V, Hf and Re, were employed to alloy the NbMoTaW RHEA and improve its mechanical properties. The alloying elements with high melting temperatures over 1850 °C were merely chosen in order to not weaken the alloy's high temperature resistance. The mechanical properties of the alloyed NbMoTaWX (X = Cr, Zr, V, Hf and Re) RHEAs were predicted by theoretical calculations combined with experimental verifications. The influence of alloying elements on the mechanical properties of NbMoTaWX (X = Cr, Zr, V, Hf and Re) RHEAs was investigated at the atomic scale based on the bonding strength and electronic structure.
Section snippets
Computational details
First-principle calculation of NbMoTaWX (X = Cr, Zr, V, Hf and Re) RHEAs was carried out using CASTEP [20,21] based on density functional theory (DFT) [22,23]. Fig. 1 is the alloys’ models. Supercell models of 1 × 1 × 5 were established for all the alloys using special quasi-random supercell method (SQS) [24] and five atoms were distributed randomly. Generalized Gradient Approximation (GGA) [25] and Perdew Burke Ernzerhof (PBE) function [26,27] were employed to portray the electronic
Phase structure
HEAs are normally reported to form FCC, BCC or HCP solid solution structures [15,17]. It is necessary to firstly investigate the phase structures of the alloyed NbMoTaWX RHEAs. Generally, average valence electron concentration VEC and atomic size difference δ were used to predict the phase structure of high entropy alloys [[30], [31], [32]]. They are described as the following formula:here, are mole fraction, atomic radius,
Conclusion
The phase structure, elastic properties, and electronic structure of alloyed NbMoTaWX (X = Cr, Zr, V, Hf and Re) RHEAs were predicted and the effect of alloying elements on the mechanical performance was investigated based on first-principle calculation and experiments. The δ, VEC, Ef, and Ec indicate that the alloyed NbMoTaWX RHEAs have a BCC single-phase solid solution structure. Most of the alloying elements (X = Cr, Zr, V, Hf and Re) enhanced the strength of NbMoTaW RHEA, while only
CRediT authorship contribution statement
Yonggang Tong: Formal analysis, Data curation, Writing - original draft, contributed the central idea, analyzed most of the data, and wrote the initial draft of the paper. The remaining authors contributed to refining the ideas, carrying out additional analyses and finalizing this paper. Linhui Bai: Formal analysis, Data curation, Writing - original draft, contributed the central idea, analyzed most of the data, and wrote the initial draft of the paper. The remaining authors contributed to
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by National Key R&D Program of China (No. 2018YFC1902401), Natural Science Foundation of Hunan Province of China (No. 2019JJ50657), Hunan Key R&D Project (No. 2019kj001), Educational Commission of Hunan Province of China (No. 18C0210) and the “Double First-Class” Scientific Research International Cooperation and Development Project of Changsha University of Science and Technology.
References (45)
- et al.
Vanadium is an optimal element for strengthening in both fcc and bcc high-entropy alloys
Acta Mater.
(2020) - et al.
Design of a dual-phase hcp-bcc high entropy alloy strengthened by ω nanoprecipitates in the Sc-Ti-Zr-Hf-Re system
Mater. Design
(2020) - et al.
Unique high-temperature deformation dominated by grain boundary sliding in heterogeneous necklace structure formed by dynamic recrystallization in HfNbTaTiZr BCC refractory high entropy alloy
Acta Mater.
(2020) - et al.
A critical review of high entropy alloys and related concepts
Acta Mater.
(2017) - et al.
Microstructures and properties of high-entropy alloys
Prog. Mater. Sci.
(2014) - et al.
Phase equilibria, microstructure, and high temperature oxidation resistance of novel refractory high entropy alloys
J. Alloys Compd.
(2015) - et al.
Enhanced mechanical properties of HfMoTaTiZr and HfMoNbTaTiZr refractory high-entropy alloys
Intermetallics
(2015) - et al.
Microstructure and oxidation behavior of new refractory high entropy alloys
J. Alloys Compd.
(2014) - et al.
Refractory high-entropy alloys
Intermetallics
(2010) - et al.
Mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys
Intermetallics
(2011)
Effect of Ti additions on mechanical properties of NbMoTaW and VNbMoTaW refractory high entropy alloys
Intermetallics
Microstructures and mechanical properties of TixNbMoTaW refractory high-entropy alloys
Mater. Sci. Eng. A
Microstructure and mechanical properties of RexNbMoTaW high-entropy alloys prepared by arc melting using metal powders
J. Alloys Compd.
Microstructure and mechanical property of a novel ReMoTaW high-entropy alloy with high density
Int. J. Refract. Met. H
Unique mechanical properties of Cu/(NbMoTaW) nanolaminates
Scripta. Mater.
Solution of the Schrödinger equation by a spectral method
J. Comput. Phys.
Composition design of high entropy alloys using the valence electron concentration to balance strength and ductility
Acta. Mater.
Phase selection motifs in High Entropy Alloys revealed through combinatorial methods: large atomic size difference favors BCC over FCC
Acta. Mater.
Prediction of structure and elastic properties of AlCrFeNiTi system high entropy alloys
Intermetallics
First-principle calculation investigation of NbMoTaW based refractory high entropy alloys
J. Alloys Compd.
An ab initio and experimental studies of the structure, mechanical parameters and state density on the refractory high-entropy alloy systems
J. Alloys Compd.
Elastic properties of the TiZrNbTaMo multi-principal element alloy studied from first principles
Intermetallics
Cited by (68)
Phase stability and mechanical properties of Ta enriched TiTaNbZrMo refractory high entropy alloys
2024, Journal of Alloys and CompoundsAchieving excellent strength and ductility of Ti<inf>2</inf>ZrNbHfV<inf>x</inf> refractory high-entropy alloys by V addition
2024, International Journal of Refractory Metals and Hard MaterialsEffects of Hf and C on microstructure and mechanical properties of Re<inf>0.1</inf>Hf<inf>x</inf>Ta<inf>1.6</inf>W<inf>0.4</inf>(TaC)<inf>y</inf> refractory medium-entropy alloy
2024, International Journal of Refractory Metals and Hard MaterialsStrengthening of Ta-W alloys by alloying Zr elements: First-principles calculation and experimental perspective
2024, Journal of Alloys and Compounds
- 1
YG Tong and LH Bai contribute equally to the article.