Phase field modeling of Spinodal decomposition in TiAlN
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
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.
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1545
IdentifiersURN: urn:nbn:se:liu:diva-79611Local ID: LIU-TEK-LIC-2012:30ISBN: 978-91-7519-836-1OAI: oai:DiVA.org:liu-79611DiVA: diva2:543923
2012-09-04, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Odén, Magnus, ProfessorJansson, Bo, ProfessorHultman, Lars, Professsor
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