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Inherent toughness and fracture mechanisms of refractory transition-metal nitrides via density-functional molecular dynamics
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.ORCID iD: 0000-0002-1379-6656
2018 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 151, p. 11-20Article in journal (Refereed) Published
Abstract [en]

Hard refractory transition-metal nitrides possess unique combinations of outstanding mechanical and physical properties, but are typically brittle. Recent experimental results demonstrated that single-crystal NaCI-structure (B1) V0.5Mo0.5N pseudobinary solid solutions are both hard (similar to 20 GPa) and ductile; that is, they exhibit toughness, which is unusual for ceramics. However, key atomic-scale mechanisms underlying this inherent toughness are unknown. Here, I carry out density-functional ab initio molecular dynamics (AIMD) simulations at room temperature to identify atomistic processes and associated changes in the electronic structure which control strength, plasticity, and fracture in V0.5Mo0.5N, as well as reference B1 TiN, subject to amp;lt;001amp;gt; and amp;lt;110amp;gt; tensile deformation. AIMD simulations reveal that V0.5Mo0.5N is considerably tougher than TiN owing to its ability to (i) isotropically redistribute mechanical stresses within the elastic regime, (ii) dissipate the accumulated strain energy by activating local structural transformations beyond the yield point. In direct contrast, TiN breaks in brittle manner when applied stresses reach its tensile strength. Charge transfer maps show that the adaptive mechanical response of V0.5Mo0.5N originates from highly populated d-d metallic-states, which allow for counterbalancing the destabilization induced via tensile deformation by enabling formation of new chemical bonds. The high ionic character and electron-localization in TiN precludes the possibility of modifying bonding geometries to accommodate the accumulated stresses, thus suddenly causing materials fracture for relatively low strain values. 

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD , 2018. Vol. 151, p. 11-20
Keywords [en]
Refractory transition-metal nitrides; Ab initio molecular dynamics; Toughness; Fracture; Electronic structures
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-148240DOI: 10.1016/j.actamat.2018.03.038ISI: 000432760300002OAI: oai:DiVA.org:liu-148240DiVA, id: diva2:1213611
Note

Funding Agencies|Olle Engkvist Foundation

Available from: 2018-06-05 Created: 2018-06-05 Last updated: 2019-06-28

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The full text will be freely available from 2020-03-26 17:47
Available from 2020-03-26 17:47

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