Thermodynamic instability of a nanocrystalline, single-phase TiZrNbHfTa alloy and its impact on the mechanical properties

Schuh, Benjamin; Völker, Bernhard; Todt, Juraj; Schell, Norbert; Perrière, Loïc; Li, J.; Couzinié, Jean-Philippe; Hohenwarter, Anton

doi:10.1016/j.actamat.2017.09.035

Cited by 226 publications

(127 citation statements)

References 47 publications

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“…The 5 element HfNbTaTiZr alloy was studied in Refs. [35,36]. It has lower Ta + Zr content than NbTaTiZr, Nb 0.5 TaTiZr 1.5 and TaTiZr studied in the present work.…”

Section: Alloymentioning

confidence: 53%

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Microstructure and Room Temperature Mechanical Properties of Different 3 and 4 Element Medium Entropy Alloys from HfNbTaTiZr System

Zýka

Málek

Veselý

et al. 2019

Entropy

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Refractory high entropy alloys (HEA) are promising materials for high temperature applications. This work presents investigations of the room temperature tensile mechanical properties of selected 3 and 4 elements medium entropy alloys (MEA) derived from the HfNbTaTiZr system. Tensile testing was combined with fractographic and microstructure analysis, using scanning electron microscope (SEM), wavelength dispersive spectroscope (WDS) and X-Ray powder diffraction (XRD). The 5 element HEA alloy HfNbTaTiZr exhibits the best combination of strength and elongation while 4 and 3 element MEAs have lower strength. Some of them are ductile, some of them brittle, depending on microstructure. Simultaneous presence of Ta and Zr in the alloy resulted in a significant reduction of ductility caused by reduction of the BCC phase content. Precipitation of Ta rich particles on grain boundaries reduces further the maximum elongation to failure down to zero values.Entropy 2019, 21, 114 2 of 17 Different elements are used to fabricate HEAs. Although the number of possible 4 or 5 elements combinations is enormous five basic metallic HEA groups can be distinguished: FCC HEAs based on the Cantor alloy, BCC refractory metal HEAs, light element HEAs, HCP HEAs and precious functional HEAs [7]. Ceramic HEAs have been established as well [8,9].Our attention was attracted by the refractory HEA group, which is composed of elements from IV, V and VI groups of the periodic table of elements [10]. These elements are characterized by prevailing good mutual miscibility and high melting points. The melting point of titanium (1668 • C) is the lowest among them. Therefore HEAs composed of these elements are intended for high temperature applications. Moreover some of these elements are biocompatible [11]. Therefore some of these alloys can be attractive for bioimplant related materials research. Note that β-Ti alloys used in bioimplant research are usually composed of this group of elements [12]. Several biocompatible HEAs have been already studied [13][14][15][16]. Also, hard ceramic composites were produced from the metals from IV, V and VI groups of the periodic table [17].Original definition of HEAs with single phase solid solution microstructure and good room temperature mechanical properties, especially ductility, is beneficial also for use in human medicine. Inspiration can be found also in other materials used for production of bioimplants which are used or have been used in other parts of material research, for example, TiAl6V4 in aerospace, CoCrMo in aero engines.Our first attempt in research of HEAs was therefore related to HfNbTaTiZr refractory metal alloy [18]. Our research was inspired by Senkov [19] and confirmed our expectations. Ingots produced by vacuum arc melting possessed single phase solid solution microstructure, with a high room temperature tensile strength and ductility.Some of the elements used in the HfNbTaTiZr alloy are very similar to each other with very similar chemical behaviour; Nb is chemically similar to Ta and Zr to ...

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“…The 5 element HfNbTaTiZr alloy was studied in Refs. [35,36]. It has lower Ta + Zr content than NbTaTiZr, Nb 0.5 TaTiZr 1.5 and TaTiZr studied in the present work.…”

Section: Alloymentioning

confidence: 53%

“…Existence of two BCC phases was reported in similar RHEA system with Mo and V instead of Ta and Nb [34]. CALPHAD simulation of the HfNbTaTiZr was performed, too [35]. A mixture of BCC and HCP phases with Ta Zr segregation was predicted.…”

Section: Ti-tamentioning

confidence: 87%

Microstructure and Room Temperature Mechanical Properties of Different 3 and 4 Element Medium Entropy Alloys from HfNbTaTiZr System

Zýka

Málek

Veselý

et al. 2019

Entropy

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“…Of these, load transfer and precipitation strengthening are considered to be the two most effective strengthening mechanisms. Excessive amounts of strong phases lead to a notable decrease in ductility or even failure before yielding during mechanical testing ( 25 ). Precipitates are often observed in HEAs when a significantly positive enthalpy of mixing (or significantly negative enthalpy of formation of intermetallic phases) cannot be counteracted by a high entropy of mixing ( 17 , 27 , 28 ).…”

Section: Introductionmentioning

confidence: 99%

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

et al. 2018

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“…It seems reassuring that the available literature on refractory HEAs (as recently reviewed in Ref. [8]) points to HfNbTiZr and derived compositions (e.g., HfNbTaTiZr and Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr, not investigated here) as currently being among the best room-temperature ductile refractory HEAs (tensile ductility larger than 10 %, compressive ductility in excess of 50 % [3,7,27,71]). (Refractory HEAs experiencing strain-induced or stress-induced phase transformations can show higher tensile elongation at fracture.)…”

Section: Discussionmentioning

confidence: 65%

Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys

Irving

et al. 2020

Acta Materialia

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Understanding the strengthening and deformation mechanisms in refractory high-entropy alloys (HEAs), proposed as new high-temperature material, is required for improving their typically insufficient room-temperature ductility. Here, density-functional theory simulations and a continuum mechanics analysis were conducted to systematically investigate the competition between cleavage decohesion and dislocation emission from a crack tip in the body-centered cubic refractory HEAs HfNbTiZr, MoNbTaVW, MoNbTaW, MoNbTiV, and NbTiVZr. This crack-tip competition is evaluated for tensile loading and a totality of 15 crack configurations and slip systems. Our results predict that dislocation plasticity at the crack tip is generally unfavorable -although the competition is close for some crack orientations, suggesting intrinsic brittleness and low crack-tip fracture toughness in these five HEAs at zero temperature. Fluctuations in local alloy composition, investigated for HfNbTiZr, can locally reduce the resistance to dislocation emission for a slip system relative to the configuration average of that slip system, but do not change the dominant cracktip response. In the case of single-crystal MoNbTaW, where an experimental, room-temperature fracture-toughness value is available for a crack on a {100} plane, theoretical and experimental results agree favorably. Factors that may limit the agreement are discussed. We survey the effect of material anisotropy on preferred crack tip orientations, which are found to be alloy specific. Mixedmode loadings are found to shift the competition in favor of cleavage or dislocation nucleation, depending on crack configuration and amplified by the effect of material anisotropy on crack tip stresses.

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Thermodynamic instability of a nanocrystalline, single-phase TiZrNbHfTa alloy and its impact on the mechanical properties

Cited by 226 publications

References 47 publications

Microstructure and Room Temperature Mechanical Properties of Different 3 and 4 Element Medium Entropy Alloys from HfNbTaTiZr System

Microstructure and Room Temperature Mechanical Properties of Different 3 and 4 Element Medium Entropy Alloys from HfNbTaTiZr System

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys

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