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Thermal stability and mechanical properties of TiAlN-based multilayer and monolithic coatings
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis explores the thermal stability, microstructure, mechanical properties and cutting performance of multilayer and monolithic cubic TiAlN hard coatings. The aim is to increase the understanding of how the coatings’ microstructure and properties are affected by a layered structure when exposed to high temperatures.

The coatings were deposited on cemented carbide substrates, using a full scale industrial reactive cathodic arc evaporation system at Seco Tools AB. The thermal stability was investigated by differential scanning calorimetry and the microstructure was characterized with analytical transmission electron microscopy, x-ray diffractometry and atom probe tomography. The mechanical properties and cutting performance were studied by nanoindentation and metal machining, respectively.

The decomposition of cubic TiAlN transpire in two steps, first by an isostructural decomposition to cubic AlN- and cubic TiN-rich domains, which is followed by a phase transformation of cubic AlN to hexagonal AlN. In this work I show that the isostructural decomposition occurs in two stages, namely: Spinodal decomposition (initial stage) and coarsening (latter stage). During the initial stage, the phase separation proceeds with a constant size of the AlN- and TiN-rich domains, with a measured wavelength of ~2.8 nm. The time needed for the initial stage depends on the temperature as well as the composition. Following the spinodal decomposition, the AlN- and TiN-rich domains coarsen. The coarsening process is kinetically limited by diffusion and is not dependent on the composition.

If the cubic TiAlN is grown as a multilayer coating, with TiN as the alternating layer type, the decomposition behavior will be different. The isostructural spinodal decomposition in the multilayers starts at a lower temperature compared to the monolithic TiAlN, while the subsequent transformation from cubic AlN to hexagonal AlN is delayed to higher temperatures. The TiN-layers confine the coarsening of the hexagonal AlN resulting in smaller domains. Mechanical testing reveals that, despite the 60 vol. % of the softer TiN, the asdeposited multilayers show a similar or slightly higher hardness than the monolithic Ti0.34Al0.66N. In addition, the multilayers show a more pronounced age hardening compared to the monoliths.

For short annealing times (<1 min) at 850 °C a layer rich in AlN followed by areas rich in TiN is observed parallel to the TiAlN/TiN interfaces in the multilayer stack. This microstructural feature indicates the presence of surface directed spinodal decomposition in the multilayer coatings. The lack of a layered structure further into the TiAlN-layer is due to the growth induced elemental fluctuations, which trigger an earlier onset of the coarsening. The coherency stresses generated across the multilayer interfaces also influence the decomposition. However, in this case the surface directed spinodal decomposition is the dominating mechanism for the altered thermal stability.

Finally, during metal machining of AISI-316L stainless steel the Ti0.34Al0.66N/TiN multilayers, regardless of period, show an improved crater wear resistance compared to a Ti0.34Al0.66N monolith. The multilayer  structure and the local coherency across the multilayer interfaces, seen in the as-deposited state, is present also after the metal machining. It is further revealed that the Ti0.34Al0.66N layer decomposes to AlN- and TiN-rich domains during the cutting operation.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 76 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1474
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-84705ISBN: 978-91-7519-801-9 (print)OAI: oai:DiVA.org:liu-84705DiVA: diva2:561231
Public defence
2012-11-16, Planck, Fysikhuset, Campus Valla, Linköpings univeristet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-10-17 Created: 2012-10-17 Last updated: 2013-10-02Bibliographically approved
List of papers
1. Thermal decomposition products in arc evaporated TiAlN/TiN multilayers
Open this publication in new window or tab >>Thermal decomposition products in arc evaporated TiAlN/TiN multilayers
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2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 14, 143110- p.Article in journal (Refereed) Published
Abstract [en]

Cubic metastable Ti0.34Al0.66 N/TiN multilayers were grown by reactive arc evaporation using Ti33-Al67 and Ti cathodes in a N2 atmosphere. X-ray diffractometry and high resolution transmission electron microscopy revealed that metastable c-Ti 0.34Al0.66N partly decomposes after annealing at 900 °C into c-TiN rich and c-AlN rich phases with retained lattice coherency. Elemental mapping by energy dispersive x-ray spectroscopy showed a homogenous distribution of Ti and Al in the as-deposited 25 nm Ti0.34Al 0.66N layers. The annealed Ti0.34Al0.66N layers exhibited coherent 5 nm domains with high Al content surrounded by a high Ti content matrix. This nanostructure formation is discussed in terms of spinodal decomposition. © 2008 American Institute of Physics.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49543 (URN)10.1063/1.2998588 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
2. Thermally enhanced mechanical properties of arc evaporated Ti0.34Al0.66N/TiN multilayer coatings
Open this publication in new window or tab >>Thermally enhanced mechanical properties of arc evaporated Ti0.34Al0.66N/TiN multilayer coatings
2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 4, 044312- p.Article in journal (Refereed) Published
Abstract [en]

Cubic metastable Ti0.34Al0.66N/TiN multilayer coatings of three different periods, 25+50, 12+25, and 6+12 nm, and monoliths of Ti0.34Al0.66N and TiN where grown by reactive arc evaporation. Differential scanning calorimetry reveals that the isostructural spinodal decomposition to AlN and TiN in the multilayers starts at a lower temperature compared to the monolithic TiAlN, while the subsequent transformation from c-AlN to h-AlN is delayed to higher temperatures. Mechanical testing by nanoindentation reveals that, despite the 60 vol % TiN, the as-deposited multilayers show similar or slightly higher hardness than the monolithic Ti0.34Al0.66N. In addition, the multilayers show a more pronounced age hardening compared to the monolith. The enhanced hardening phenomena and improved thermal stability of the multilayer coatings are discussed in terms of particle confinement and coherency stresses from the neighboring TiN-layers.

Place, publisher, year, edition, pages
American Institute of Physics, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-60236 (URN)10.1063/1.3463422 (DOI)000281857100116 ()
Note

Original Publication: Axel Knutsson, M. P. Johansson, L Karlsson and Magnus Odén, Thermally enhanced mechanical properties of arc evaporated Ti0.34Al0.66N/TiN multilayer coatings, 2010, JOURNAL OF APPLIED PHYSICS, (108), 4, 044312. http://dx.doi.org/10.1063/1.3463422 Copyright: American Institute of Physics http://www.aip.org/

Available from: 2010-10-08 Created: 2010-10-08 Last updated: 2017-12-12
3. Machining performance and decomposition of TiAlN/TiN multilayer coated metal cutting inserts
Open this publication in new window or tab >>Machining performance and decomposition of TiAlN/TiN multilayer coated metal cutting inserts
2011 (English)In: SURFACE and COATINGS TECHNOLOGY, ISSN 0257-8972, Vol. 205, no 16, 4005-4010 p.Article in journal (Refereed) Published
Abstract [en]

The wear resistance of metal cutting inserts coated with metastable Ti0.34Al0.66N/TiN multilayers was tested in continuous turning of an AISI 316L stainless steel. The multilayers had periods of 25 + 50, 12 + 25 and 6 + 12 nm (Ti0.34Al0.66N + TiN) with a total multilayer stack thickness of 2 mu m. Inserts coated with monolithic TiN and Ti0.34Al0.66N deposited under similar conditions were used as references. The multilayer coated inserts show a decrease of wear with decreased multilayer period, both on the rake and flank face. The wear on the rake face was lower on all the multilayer coated tools compared to the references. Scanning transmission electron imaging and energy dispersive spectroscopy elemental mapping of a worn multilayer coating show decomposition of the Ti0.34Al0.66N to domains rich of Al and Ti. High resolution transmission electron micrography shows preserved epitaxy between the TiN and Ti0.34Al0.66N layers. The improved wear resistance of the multilayer coated inserts is discussed in terms of an improved thermal stability of the multilayer stacks.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-68336 (URN)10.1016/j.surfcoat.2011.02.031 (DOI)000290187700005 ()
Available from: 2011-05-20 Created: 2011-05-20 Last updated: 2015-06-01
4. Microstructure evolution during annealing of TiAlN-coatings: A combined in-situ SAXS and phase field study
Open this publication in new window or tab >>Microstructure evolution during annealing of TiAlN-coatings: A combined in-situ SAXS and phase field study
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2011 (English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper describes in detail the microstructure evolution of Ti0.33Al0.67N and Ti0.50Al0.50N coatings during isothermal annealing studied by in-situ small angle x-ray scattering (SAXS) in combination with phase field simulations. We show that the decomposition occurs in two stages consistent with spinodal decomposition. During the initial stage, the phase segregation proceeds with a constant size of AlN- and TiN-rich domains with a radius of ~0.7 nm for 5 and 20 min at 900 and 850 C respectively in the Ti0.50Al0.50N alloy. The length of the initial stage depends on the temperature as well as the composition, and is shorter for the higher Al content coating. Following the initial stage, the AlN- and TiN-rich domains coarsen. The decomposition process is discussed in terms of Gibbs free energy, diffusion, and gradient energies. Scanning transmission electron microscopy and energy dispersive x-ray spectroscopy of the post annealed coatings confirm a decomposed microstructure with coherent domains rich in AlN and TiN of the same size as determined by SAXS.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-75175 (URN)
Available from: 2012-02-20 Created: 2012-02-20 Last updated: 2013-10-02Bibliographically approved
5. Surface directed spinodal decomposition at TiAlN / TiN interfaces
Open this publication in new window or tab >>Surface directed spinodal decomposition at TiAlN / TiN interfaces
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2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 11, 114305-1-114305-8 p.Article in journal (Refereed) Published
Abstract [en]

In contrast to the monolithic c-Ti1-xAlxN, the isostructural spinodal decomposition to c-AlN and c-TiN of the c-Ti1-xAlxN/TiN multilayers have the same onset temperature regardless of composition (x=0.50 and 0.66). The onset is also located at a lower temperature compared to the monoliths with the same Al-content, revealed by differential scanning calorimetry. Zcontrast STEM imaging shows a decomposed structure of the multilayers at a temperature where it is not present in the monoliths. Atom probe tomography reveal the formation of an AlN-rich layer followed by a TiN-rich area parallel to the interface in the decomposed Ti0.34Al0.66N/TiN coating, consistent with surface directed spinodal decomposition. Phase field simulations predict such behavior and show that the surface directed spinodal decomposition is affected by in the internal interfaces, as deposited elemental fluctuations, coherency stresses and alloy composition.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
Keyword
Surface directed spinodal decomposition, Titanium aluminium nitride, Phase field simulations, Atom probe tomography
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-84704 (URN)10.1063/1.4795155 (DOI)000316545200054 ()
Available from: 2012-10-17 Created: 2012-10-17 Last updated: 2017-11-07Bibliographically approved

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