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Toughness enhancement in transition metal nitrides
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. (Thin Film Physics)
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Toughness enhancements can be induced in cubic-B1 transition metal nitride alloys by an increased occupation of the d-t2g metallic states. In this Licentiate Thesis I use density functional theory to investigate the mechanical properties of TiN and VN and of the ternaries obtained by replacing 50% of Ti and V atoms with M (M = V, Nb, Ta, Mo, and W) to form ordered structures with minimum number of inter-metallic bonds. The calculated values of elastic constants and moduli show that ternary alloys with high valence electron concentrations (M = Mo and W), have large reductions in shear moduli and C44 elastic constants, while retaining the typically high stiffness and incompressibility of ceramic materials. These results point to significantly improved ductility in the ternary compounds. This important combination of strength and ductility, which equates to material toughness, stems from alloying with valence electron richer dmetals. The increased valence electron concentration strengthens metal–metal bonds by filling metallic d-t2g states, and leads to the formation of a layered electronic configuration upon shearing. Comprehensive electronic structure calculations demonstrate that in these crystals, stronger Ti/V – N and weaker M – N bonds are formed as the valence electron concentration is increased. This phenomenon ultimately enhances ductility by promoting dislocation glide through the activation of an easy slip system.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 26 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1462
Keyword [en]
cubic, transition metal nitrides, mechanical properties, ab initio, dft, toughness, ductility, electronic structure
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-63364Local ID: LIU-TEK-LIC-2011:2ISBN: 978-91-7393-257-8 (print)OAI: oai:DiVA.org:liu-63364DiVA: diva2:378914
Presentation
2011-02-03, Planck, Physics building, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2010-12-30 Created: 2010-12-16 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Electronic mechanism for toughness enhancement in TixM1-xN (M=Mo and W)
Open this publication in new window or tab >>Electronic mechanism for toughness enhancement in TixM1-xN (M=Mo and W)
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 10, 104107-104113 p.Article in journal (Refereed) Published
Abstract [en]

Toughness, besides hardness, is one of the most important properties of wear-resistant coatings. We use ab initio density-functional theory calculations to investigate the mechanical properties of ternary metal nitrides TixM1-xN, with M=Mo and W, for x=0.5. Results show that Mo and W alloying significantly enhances the toughness of TiN. The electronic mechanism responsible for this improvement, as revealed by electronic structure calculations, stems from the changes in charge density induced by the additional transition-metal atom. This leads to the formation of a layered electronic arrangement, characterized by strong, respectively, weak, directional bonding, which enables a selective response to strain, respectively, shear, deformations of the structures and yields up to 60% decrease in C-44 values.

Place, publisher, year, edition, pages
American Physical Society, 2010
Keyword
cubic, transition metal nitrides, mechanical properties, ab initio, dft, ductility, toughness, electronic structure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-54851 (URN)10.1103/PhysRevB.81.104107 (DOI)000276248700040 ()
Note
Original Publication: Davide Sangiovanni, Valeriu Chirita and Lars Hultman, Electronic mechanism for toughness enhancement in TixM1-xN (M=Mo and W), 2010, PHYSICAL REVIEW B, (81), 10, 104107. http://dx.doi.org/10.1103/PhysRevB.81.104107 Copyright: American Physical Society http://www.aps.org/ Available from: 2010-04-16 Created: 2010-04-16 Last updated: 2016-08-31
2. Supertoughening in B1 transition metal nitride alloys by increased valence electron concentration
Open this publication in new window or tab >>Supertoughening in B1 transition metal nitride alloys by increased valence electron concentration
2011 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, no 5, 212-2134 p.Article in journal (Refereed) Published
Abstract [en]

We use density functional theory calculations to explore the effects of alloying cubic TiN and VN with transition metals M = Nb, Ta, Mo, W in 50% concentrations. The obtained ternaries are predicted to become supertough as they are shown to be harder and significantly more ductile compared to the reference binaries. The primary electronic mechanism of this supertoughening effect is shown in a comprehensive electronic structure analysis of these compounds to be the increased valence electron concentration intrinsic to these ternaries. Our investigations reveal the complex nature of chemical bonding in these compounds, which ultimately explains the observed selective response to stress. The findings presented in this paper thus offer a design route for the synthesis of supertough transition metal nitride alloys via valence electron concentration tuning.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Cubic, transition metal nitrides, mechanical properties, ab initio, dft, ductility, toughness, electronic structure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-63361 (URN)10.1016/j.actamat.2010.12.013 (DOI)000287775400026 ()
Funder
Swedish Research Council
Note
On the defence day the status of the article was: Accepted. Original Publication: Davide Giuseppe Sangiovanni, Lars Hultman and Valeriu Chirita, Supertoughening in B1 transition metal nitride alloys by increased valence electron concentration, 2011, Acta Materialia, (59), 5, 212-2134. http://dx.doi.org/10.1016/j.actamat.2010.12.013 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-12-16 Created: 2010-12-16 Last updated: 2017-12-11Bibliographically approved
3. Structure and mechanical properties of TiAlN-WNx thin films
Open this publication in new window or tab >>Structure and mechanical properties of TiAlN-WNx thin films
Show others...
2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550Article in journal (Refereed) Submitted
Keyword
cubic, transition metal nitrides, quarternary, alloys, hardness
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-63362 (URN)
Available from: 2010-12-16 Created: 2010-12-16 Last updated: 2017-12-11Bibliographically approved

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