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Microstructure evolution during annealing of TiAlN-coatings: A combined in-situ SAXS and phase field study
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439 USA.
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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.

Place, publisher, year, edition, pages
2011.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-75175OAI: oai:DiVA.org:liu-75175DiVA: diva2:504310
Available from: 2012-02-20 Created: 2012-02-20 Last updated: 2013-10-02Bibliographically approved
In thesis
1. High temperature behavior of arc evaporated ZrAlN and TiAlN thin films
Open this publication in new window or tab >>High temperature behavior of arc evaporated ZrAlN and TiAlN thin films
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hard coatings can extend the life time of a tool substantially and enable higher cutting speeds which increase the productivity in the cutting application. The aim with this thesis is to extend the understanding on how the microstructure and mechanical properties are affected by high temperatures similar to what a cutting tool can reach during operation.

Thin films of ZrAlN and TiAlN have been deposited using cathodic arc-evaporation. The microstructure of as-deposited and annealed films has been studied using electron microscopy and x-ray scattering. The thermal stability has been characterized by calorimetry and thermogravity and the mechanical properties have been investigated by  nanoindentation.

The microstructure of Zr1−xAlxN thin films was studied as a function of composition, deposition conditions, and annealing temperature. The structure was found to depend on the Al content where a low (x < 0.38) Al-content results in cubic-structured ZrAlN while for x > 0.70 the structure is hexagonal. For intermediate Al contents (0.38 < x < 0.70), a  nanocomposite structure with a mixture of cubic, hexagonal and amorphous phases is obtained.

The cubic ZrAlN phase transforms by nucleation and growth of hexagonal AlN when annealed above 900 C. Annealing of hexagonal ZrAlN thin films (x > 0.70) above 900 C causes formation of AlN and ZrN rich domains within the hexagonal lattice. Annealing of nanocomposite ZrAlN thin films results in formation of cubic ZrN and hexagonal AlN. The transformation is initiated by nucleation and growth of cubic ZrN at temperatures of 1100 C while the AlN-rich domains are still amorphous or nanocrystalline. Growth of hexagonal AlN is suppressed by the high nitrogen content of the films and takes place at annealing temperatures of 1400 C.

In the more well known TiAlN system, the initial stage of decomposition is spinodal with formation of cubic structured domains enriched in TiN and AlN. By a combination of in-situ xray scattering techniques during annealing and phase field simulations, both the microstructure that evolves during decomposition and the decomposition rate are found to depend on the composition. The results further show that early formation of hexagonal AlN domains during decomposition can cause formation of strains in the cubic TiAlN phase.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 78 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1428
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-75176 (URN)978-91-7519-956-6 (ISBN)
Public defence
2012-03-22, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-02-20 Created: 2012-02-20 Last updated: 2016-08-31Bibliographically approved
2. Thermal stability and mechanical properties of TiAlN-based multilayer and monolithic coatings
Open this publication in new window or tab >>Thermal stability and mechanical properties of TiAlN-based multilayer and monolithic coatings
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:nbn:se:liu:diva-84705 (URN)978-91-7519-801-9 (ISBN)
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

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Knutsson, AxelUllbrand, JenniferRogström, LinaOdén, Magnus

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