Local lattice distortions and the structural instabilities in bcc Nb–Ta–Ti–Hf high-entropy alloys: An ab initio computational study

Borges, Pedro P.P.O.; Ritchie, Robert O.; Asta, Mark

doi:10.1016/j.actamat.2023.119415

Cited by 5 publications

(2 citation statements)

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“…These results do not consider the effects of short-range order. Although the low mixing energies of Nb, Ta, Ti, and Hf in this alloy suggest that it would have a low tendency to order, implying that this would have a minimal impact on GSFEs ( 28 ), the presence of short-range order can alter stacking fault energy, as is the case in the CrCoNi alloy ( 56 ). The addition of group IV elements (in this case, Ti and Hf) is essential to the formation of kink bands because these elements promote slip on <111>{112}.…”

Section: Resultsmentioning

confidence: 93%

“…Specifically, we investigated the mechanical properties of a nonequiatomic Nb 45 Ta 25 Ti 15 Hf 15 RMEA from 77 to 1473 K by performing uniaxial tensile tests and nonlinear elastic J-integral–based fracture toughness tests. The material was designed by alloying group IV elements (Ti and Hf) with group V elements (Nb and Ta) to (i) ductilize the material, (ii) generate lattice distortion to allow for high-temperature strength retention, and most notably, (iii) to prioritize high-temperature bcc thermodynamic stability lacking in RHEAs containing Zr and with higher concentations of group IV elements ( 28 , 29 ). More information on the details of the alloy design can be found in ( 30 ).…”

Section: Resultsmentioning

confidence: 99%

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Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy

Cook,

Kumar,

Payne

et al. 2024

Science

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Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy’s behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m 1/2 , which we attribute to a dynamic competition between screw and edge dislocations in controlling the plasticity at a crack tip. Whereas the glide and intersection of screw and mixed dislocations promotes strain hardening controlling uniform deformation, the coordinated slip of <111> edge dislocations with {110} and {112} glide planes prolongs nonuniform strain through formation of kink bands. These bands suppress strain hardening by reorienting microscale bands of the crystal along directions of higher resolved shear stress and continually nucleate to accommodate localized strain and distribute damage away from a crack tip.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy

Cook,

Kumar,

Payne

et al. 2024

Science

Self Cite

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Atomistic Simulations of the Shock and Spall Behavior of the Refractory High-Entropy Alloy HfNbTaTiZr

Thürmer,

Deluigi,

Urbassek

et al. 2024

High Entropy Alloys & Materials

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Using molecular dynamics simulation, we study the effect of a shock wave on the refractory high-entropy alloy HfNbTaTiZr. A single-crystalline sample, shocked along the [001] direction, is considered. The initial compression leads to only weak dislocation activity and a bcc $$\rightarrow$$ → hcp transformation in some regions of the sample. After the shock wave is reflected from the free back surface of the sample, hcp transforms back to bcc, and twins are formed in the bcc phase. The sample spalls under the high tensile pressures developing after wave reflection. In this stage, we observe dislocation activity from the twin boundaries and inside the nanograins generated by twinning. Under the large tensile stresses, some fcc phase appears together with disordered amorphous regions where voids nucleate and lead to spall. The fracture surfaces follow the twin boundaries set up in the compression phase. The spall strength is similar to the one found in simulations of other bcc metals at similar strain rates. Similar simulations for the equiatomic HfNbTaZr HEA show the same qualitative behavior, with twins and reduced dislocation activity, but without phase transformations.

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Interaction of C, N and O interstitial solute atoms with screw dislocations in HfNbTaTiZr high entropy alloy

Leveau,

Ventelon,

Clouet

2024

Acta Materialia

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Local lattice distortions and the structural instabilities in bcc Nb–Ta–Ti–Hf high-entropy alloys: An ab initio computational study

Cited by 5 publications

References 70 publications

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy

Atomistic Simulations of the Shock and Spall Behavior of the Refractory High-Entropy Alloy HfNbTaTiZr

Interaction of C, N and O interstitial solute atoms with screw dislocations in HfNbTaTiZr high entropy alloy

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