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Phase field modeling of Spinodal decomposition in TiAlN
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

TiAlN  thin  films  are  used  commercially  in  the  cutting  tool  industry  as  wear protection  of  the  inserts.  During  cutting,  the  inserts  are  subjected  to  high temperatures (~ 900  ° C and sometimes higher). The  objective of this work is to simulate the material behavior at such high temperatures. TiAlN has been studied experimentally at least for two decades, but no microstructure simulations have so far been performed. In this thesis two models are presented, one based on regular solution and one that takes into account clustering effects on the thermodynamic data. 

Both  models  include  anisotropic  elasticity  and  lattice  parameters  deviation from  Vegard’s  law.  The  input  parameters  used  in  the  simulations  are ab  initio calculations and experimental data.Methods for extracting diffusivities and activation energies as well as Young’s modulus  from  phase  field  results  are  presented.  Specifically,  strains,  von  Mises stresses,  energies,  and  microstructure  evolution  have  been  studied  during  the spinodal  decomposition of  TiAlN. It  has  been  found  that  strains  and  stresses  are generated during the decomposition i.e. von Mises stresses ranging between 5 and 7.5  GPa  are  typically  seen.  The  stresses  give  rise  to  a  strongly  composition dependent  elastic  energy  that  together  with  the  composition  dependent  gradient energy   determine   the   decomposed   microstructure.   Hence,   the   evolving microstructure depends strongly on the global composition. Morphologies ranging from isotropic, round domains to entangled outstretched domains can be achievedby  changing  the  Al  content.  Moreover,  the  compositional  wavelength  of  the evolved  domains  during  decomposition  is  also  composition  dependent  and  it decreases with  increasing  Al  content.  Comparing  the  compositional  wavelength evolution extracted from simulations and small angle X-ray scattering experiments show that the decomposition of TiAlN occurs in two stages; first an initial stage of constant  wavelength and  then  a  second  stage  with  an  increasing  wavelength are observed.  This  finding  is  characteristic  for  spinodal  decomposition  and  offers conclusive evidence that an ordering transformation occurs. The Young’s modulus evolution  for  Ti 0.33 Al 0.67 N  shows  an  increase  of  5%  to  ~398  GPa  during  the simulated decomposition.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 72 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1545
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-79611Local ID: LIU-TEK-LIC-2012:30ISBN: 978-91-7519-836-1 (print)OAI: oai:DiVA.org:liu-79611DiVA: diva2:543923
Presentation
2012-09-04, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-08-20 Created: 2012-08-10 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Strain evolution during spinodal decomposition of TiAlN thin films
Open this publication in new window or tab >>Strain evolution during spinodal decomposition of TiAlN thin films
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2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 17, 5542-5549 p.Article in journal (Refereed) Published
Abstract [en]

We use a combination of in-situ x-ray scattering experiments during annealing and phase-field simulations to study the strain and microstructure evolution during decomposition of TiAlN thin films. The evolved microstructure is observed to depend on composition, where the larger elastic anisotropy of higher Al content films causes formation of elongated AlN and TiN domains. The simulations show strain formation in the evolving cubic-AlN and TiN domains, which is a combined effect of increasing lattice mismatch and elastic incompatibility between the domains. The experimental results show an increased compressive strain in the TiAlN phase during decomposition due to the onset of transformation to hexagonal-AlN.

Place, publisher, year, edition, pages
Elsevier, 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-75174 (URN)10.1016/j.tsf.2012.04.059 (DOI)000305770200010 ()
Available from: 2012-02-20 Created: 2012-02-20 Last updated: 2017-12-07Bibliographically approved
2. Early stage spinodal decomposition and microstructure evolution in TiAlN: A combined in-situ SAXS and phase field study
Open this publication in new window or tab >>Early stage spinodal decomposition and microstructure evolution in TiAlN: A combined in-situ SAXS and phase field study
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper describes in detail the microstructure and phase evolution in 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 isostructural spinodal decomposition occurs in two stages. During the initial stage, the phase segregation proceeds with a constant size of AlN- and TiN-rich domains with an experimentally measured 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 temperature as well as metal composition, and is shorter for the higher Al-content  coating. After the initial stage, the coherent cubic AlN- and TiN-rich domains coarsen. The coarsening process is kinetically limited by diffusion, which allowed us to estimate the diffusivity and activation energies of the metals to 1.4·10-7 m2s-1 and 3.14 eV at-1 respectively.

Keyword
TiAlN, Phase-field simulations, Spinodal decomposition, SAXS, High energy x-ray diffraction, Coarsening
National Category
Ceramics
Identifiers
urn:nbn:se:liu:diva-79607 (URN)
Available from: 2012-08-10 Created: 2012-08-10 Last updated: 2016-08-31Bibliographically approved
3. Microstructure evolution of TiAlN-a phase field study
Open this publication in new window or tab >>Microstructure evolution of TiAlN-a phase field study
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this work the phase field method has been applied to model the spinodal decomposition of TiAlN. Here we have used thermodynamic data from ab initio calculations that takes into account clustering effects, and experimental diffusivity data of TiAlN as an input to the model. The effect of alloy composition on microstructure and stresses, is studied in time and space. In addition, Young’s modulus evolution of the decomposing microstructure is reported. It was found that the microstructure changes from round AlN rich domains in a TiN matrix, to outstretched TiN rich domains in the {100} crystallographic directions in an AlN matrix, as the composition was changed from x=0.3 to x=0.75 in Ti1-xAlxN. The microstructure evolution was observed to undergo different stages. In short; first elongated structures enriched of the majority element in random directions evolve. Thereafter round AlN rich domains evolve, independent of composition studied, and a completely segregated microstructure forms that finally coarsens. The initiation, decomposition, and coarsening rate was found to increase with Al content due to the increase in driving force with Al content. Al rich domains purify fastest, independent of composition studied. The evolving compositional wavelength decreases with Al content resulting in a finer microstructure for alloys rich in Al. During decomposition high local strains and stresses develop, which reach maximum values of 6·10-3 and 12 GPa respectively.

National Category
Ceramics
Identifiers
urn:nbn:se:liu:diva-79608 (URN)
Available from: 2012-08-10 Created: 2012-08-10 Last updated: 2013-10-02Bibliographically approved

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Ullbrand, Jennifer

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