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

David H Cook; Punit Kumar; Madelyn I Payne; Calvin H Belcher; Pedro Borges; Wenqing Wang; Flynn Walsh; Zehao Li; Arun Devaraj; Mingwei Zhang; Mark Asta; Andrew M Minor; Enrique J Lavernia; Diran Apelian; Robert O Ritchie

doi:10.1126/science.adn2428

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

Science. 2024 Apr 12;384(6692):178-184. doi: 10.1126/science.adn2428. Epub 2024 Apr 11.

Authors

David H Cook^#^{1

2}, Punit Kumar^#², Madelyn I Payne^{1

2}, Calvin H Belcher³, Pedro Borges^{1

2}, Wenqing Wang^{1

2}, Flynn Walsh^{1

2}, Zehao Li⁴, Arun Devaraj⁴, Mingwei Zhang^{2

5}, Mark Asta^{1

2}, Andrew M Minor^{1

2

5}, Enrique J Lavernia³, Diran Apelian³, Robert O Ritchie^{1

2}

Affiliations

¹ Department of Materials Science and Engineering, University of California, Berkeley, CA, USA.
² Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
³ Department of Materials Science and Engineering, University of California, Irvine, CA, USA.
⁴ Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, USA.
⁵ National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.

^# Contributed equally.

PMID: 38603511
DOI: 10.1126/science.adn2428

Abstract

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.