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Electronic mechanism for toughness enhancement in TixM1-xN (M=Mo and W)
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. (Thin Film Physics)
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. (Thin Film Physics)
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. (Thin Film Physics)ORCID iD: 0000-0002-2837-3656
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. Vol. 81, no 10, 104107-104113 p.
Keyword [en]
cubic, transition metal nitrides, mechanical properties, ab initio, dft, ductility, toughness, electronic structure
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-54851DOI: 10.1103/PhysRevB.81.104107ISI: 000276248700040OAI: oai:DiVA.org:liu-54851DiVA: diva2:310865
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: 2017-12-12
In thesis
1. Toughness enhancement in transition metal nitrides
Open this publication in new window or tab >>Toughness enhancement in transition metal nitrides
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
cubic, transition metal nitrides, mechanical properties, ab initio, dft, toughness, ductility, electronic structure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-63364 (URN)LIU-TEK-LIC-2011:2 (Local ID)978-91-7393-257-8 (ISBN)LIU-TEK-LIC-2011:2 (Archive number)LIU-TEK-LIC-2011:2 (OAI)
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
2. Transition Metal Nitrides: Alloy Design and Surface Transport Properties using Ab-initio and Classical Computational Methods
Open this publication in new window or tab >>Transition Metal Nitrides: Alloy Design and Surface Transport Properties using Ab-initio and Classical Computational Methods
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Enhanced toughness in brittle ceramic materials, such as transition metal nitrides (TMN), is achieved by optimizing the occupancy of shear-sensitive metallic electronic-states. This is the major result of my theoretical research, aimed to solve an inherent long-standing problem for hard ceramic protective coatings: brittleness. High hardness, in combination with high toughness, is thus one of the most desired mechanical/physical properties in modern coatings. A significant part of this PhD Thesis is dedicated to the density functional theory (DFT) calculations carried out to understand the electronic origins of ductility, and to predict novel TMN alloys with optimal hardness/toughness ratios. Importantly, one of the TMN alloys identified in my theoretical work has subsequently been synthesized in the laboratory and exhibits the predicted properties.

The second part of this Thesis concerns molecular dynamics (MD) simulations of Ti, N, and TiNx adspecies diffusion on TiN surfaces, chosen as a model material, to provide unprecedented detail of critical atomic-scale transport processes, which dictate the growth modes of TMN thin films. Even the most advanced experimental techniques cannot provide sufficient information on the kinetics and dynamics of picosecond atomistic processes, which affect thin films nucleation and growth. Information on these phenomena would allow experimentalists to better understand the role of deposition conditions and fine tune thin films growth modes, to tailor coatings properties to the requirements of different applications. The MD simulations discussed in the second part of this PhD Thesis, predict that Ti adatoms and TiN2 admolecules are the most mobile species on TiN(001) terraces. Moreover, these adspecies are rapidly incorporated at island descending steps, and primarily contribute to layer-by-layer growth. In contrast, TiN3 tetramers are found to be essentially stationary on both TiN(001) terraces and islands, and thus constitute the critical nuclei for three-dimensional growth.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 75 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1513
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-91379 (URN)978-91-7519-638-1 (ISBN)
Public defence
2013-05-23, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-04-23 Created: 2013-04-23 Last updated: 2016-08-31Bibliographically approved

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Sangiovanni, Davide GiuseppeChirita, ValeriuHultman, Lars

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