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Self-organized nanostructures in the Ti-Al-N system
University of Leoben. (Department of Physical Metallurgy and Materials Testing)
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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2003 (English)In: Applied Physics Letters, ISSN 0003-6951, Vol. 83, no 10, 2049-2051 p.Article in journal (Refereed) Published
Abstract [en]

The phenomenon of age hardening could be evidenced in thin film applications. A model system, Ti1-xAlxN was chosen as such coatings are known for their excellent wear resistance enabling improved machining processes like high-speed and dry cutting. Here, we show unambiguously that metastable Ti1-xAlxN coatings initially undergo spinodal decomposition into coherent cubic-phase nanometer-size domains, causing an increase in hardness at elevated temperatures. These intermediate metastable domains transform into their stable phases TiN and AlN during further thermal treatment. Activation energies for the processes indicate defect-assisted segregation of Ti and Al. The findings are corroborated by ab initio calculations. A long-standing discussion on the thermal stability of this important class of ceramics is thus resolved.

Place, publisher, year, edition, pages
2003. Vol. 83, no 10, 2049-2051 p.
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-18822DOI: 10.1063/1.1608464OAI: oai:DiVA.org:liu-18822DiVA: diva2:221712
Available from: 2009-06-08 Created: 2009-06-05 Last updated: 2016-08-31Bibliographically approved
In thesis
1. Arc evaporated wear-resistant nitride coatings for metal cutting tools
Open this publication in new window or tab >>Arc evaporated wear-resistant nitride coatings for metal cutting tools
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This Thesis is dedicated to increase the understanding of arc evaporated PVD coatings as wear resistant layers on metal cutting tools. The approach is to study coatings that have excellent performance in metal cutting applications, specifically (Ti,Al)N and (Ti,Si)N in terms of thermal and mechanical properties, and to correlate this to their microstructure, stress state, and composition. The effect of addition of oxygen into (Ti,Al)N is also evaluated in terms of structure, chemical bonding, and mechanical properties. It is shown that metastable fcc-(Ti,Al)N coatings separate into Ti-rich and Al-rich fcc-(Ti,Al)N zones via spinodal decomposition at 800 - 1000 °C, which acts as a hardening mechanism. This is followed by nucleation and growth into the stable phases fcc-TiN and hex-AlN at T>1000°C, with subsequent loss of hardness. These structural changes are correlated to the cutting performance, showing that the initial spinodal phase separation improves the performance. The success of (Ti,Al)N in metal cutting applications is, hence, due not only to the well documented oxidation resistance, but also to the spinodal decomposition process, which is active at the typical temperatures at the cutting edge of an engaged cutting insert. The potential subsequent renucleation process is, however, detrimental in metal cutting applications. Oxygen is commonly regarded as a contamination in PVD coating processes due to the risk of formation of insulating layers. This study, however, shows that by using arcevaporation, up to 35 at.% O can be incorporated into (Ti,Al)N coatings without altering its NaCl-structure. 1t is inferred that O substitutes for N in the lattice and (Ti,Al)(O,N) is formed. The incorporation of small amounts of oxygen (up to 13 at.%) improves the cutting performance by reducing the risk of chipping. However, at higher oxygen levels, the wear resistant properties are dramatically reduced. Finally, is shown that it is poss ible to replace at least 14 at.% Ti by Si, without altering the NaCl-structure in (Ti,Si)N coatings. The measured hardness of solid solution fcc-(Ti,Si)N is nearly a linear function of Si-content in the coating (from 31 GPa in TiN up to 45 GPa in (Ti0.86Si0.14)N). The hardness is also retained after annealing at 900 oC for 2h.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2008. 33 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1375
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44911 (URN)78251 (Local ID)978-91-7393-849-5 (ISBN)78251 (Archive number)78251 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-11-22

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Hörling, AndersHultman, Lars

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