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Toughness enhancement in highly NbN-alloyed Ti-Al-N hard coatings
Comenius University, Slovakia; Institute Mat and Machine Mech, Slovakia.
Comenius University, Slovakia.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Ruhr University of Bochum, Germany.
Fac Mat Science and Technology STU, Slovakia.
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2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 121, 59-67 p.Article in journal (Refereed) Published
Abstract [en]

Obtaining high hardness combined with enhanced toughness represents one of the current challenges in material design of hard ceramic protective coatings. In this work, we combine experimental and ab initio density functional theory (DFT) analysis of the mechanical properties of Ti-Al-Nb-N coatings to validate the results of previous theoretical investigations predicting enhanced toughness in TiAIN-based systems highly alloyed (amp;gt;25 at. %) with nitrides of pentavalent VB group elements Nb, Ta, and V. As-deposited Ti1-x-yAlxNbyN coatings (y = 0 divided by 0.61) exhibit single phase cubic sodium chloride (B1) structure identified as TiAl(Nb)N solid solutions. The highest hardness,similar to 32.5 +/- 2 GPa, and the highest Youngs modulus, similar to 442 GPa, are obtained in Nb-free Ti0.46Al0.54N exhibiting pronounced 111 growth-orientation. Additions of Nb in the coatings promote texture evolution toward 200. Nanoindentation measurements demonstrate that alloying TiAlN with NbN yields significantly decreased elastic stiffness, from 442 to similar to 358 divided by 389 GPa, while the hardness remains approximately constant (between 28 +/- 2 and 31 +/- 3 GPa) for all Nb contents. DFT calculations and electronic structure analyses reveal that alloying dramatically reduces shear resistances due to enhanced d-d second-neighbor metallic bonding while retaining strong metal-N bonds which change from being primarily ionic (TiAlN) to more covalent (TiAlNbN) in nature. Overall, Nb substitutions are found to improve ductility of TiAlN-based alloys at the cost of slight losses in hardness, equating to enhanced toughness. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD , 2016. Vol. 121, 59-67 p.
Keyword [en]
Ti-Al-Nb-N; Coatings; Sputtering; ab initio calculations; Hardness; Toughness
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-132826DOI: 10.1016/j.actamat.2016.08.084ISI: 000386984500006OAI: oai:DiVA.org:liu-132826DiVA: diva2:1052877
Note

Funding Agencies|Slovak Research and Development Agency [APVV-14-0173]; Operational Program Research and Development [ITMS: 26210120010]; Ministry of Education of the Slovak Republic [VEGA 1/0876/15]

Available from: 2016-12-07 Created: 2016-11-30 Last updated: 2016-12-07

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Sangiovanni, Davide
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