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Toughness enhancement in TiAlN-based quarternary alloys
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-2837-3656
2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 11, 4080-4088 p.Article in journal (Refereed) Published
Abstract [en]

Improved toughness in hard and superhard thin films is a primary requirement for present day ceramic hard coatings, known to be prone to brittle failure during in-use conditions. We use density functional theory calculations to investigate a number of (TiAl)(1-x)MxN thin films in the B1 structure, with 0.06 andlt;= x andlt;= 0.75 obtained by alloying TiAlN with M = V, Nb, Ta, Mo and W. Results show significant ductility enhancements, hence increased toughness, in these compounds. Importantly, these thin films are also predicted to be superhard, with similar or increased hardness values, compared to Ti0.5Al0.5 N. For (TiAl)(1-x)WxN the results are experimentally confirmed. The ductility increase originates in the enhanced occupancy of d-t(2g) metallic states, induced by the valence electrons of substitutional elements (V, Nb, Ta, Mo, W). This effect is more pronounced with increasing valence electron concentration, and, upon shearing, leads to the formation of a layered electronic structure in the compound material, consisting of alternating layers of high and low charge density in the metallic sublattice, which in turn, allows a selective response to normal and shear stresses.

Place, publisher, year, edition, pages
Elsevier , 2012. Vol. 520, no 11, 4080-4088 p.
Keyword [en]
Nitrides, Titanium aluminum nitride, Hardness, Toughness, Ductility, Density Functional Theory, Metals, Quarternaries
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-77336DOI: 10.1016/j.tsf.2012.01.030ISI: 000302838800037OAI: oai:DiVA.org:liu-77336DiVA: diva2:526320
Note
Funding Agencies|Swedish Research Council (VR)||Swedish Strategic Research Foundation (SSF)||Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2017-12-07
In thesis
1. 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, DavideChirita, ValeriuHultman, Lars

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