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Phase transformations in Ti1xA1xN thin films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Seco Tools AB, Fagersta, Sweden.
Department of Physical Metallurgy and Materials Testing, University of Leoben, Austria.
Department of Physical Metallurgy and Materials Testing, University of Leoben, Austria.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We report ageing phenomena in arc-deposited Ti1-xA1xN (0≤x≤0.66) thin films probed by X-ray diffraction, differential scanning calorimetry, four-point probe sheet resistance, and transmission electron microscopy measurements. Annealing Ti1-xA1xN films at 500-900°C results in residual stress recovery through annihilation of deposition-induced lattice defects, followed by spinodal decomposition at 900-1400°C into coherent nanometer-size domains of [NaCl]-TiN, and [NaCl]-AIN that eventually transform into the stable [wurtzite]-AIN phase. Kinetics measurements reveal activation energies of 2.0-2.9 eV for lattice recovery processes, and 2.9-3.5 eV for transformation processes, indicating grain boundary and defect-assisted segregation of Ti and Al. The composition was shown to have large influence on the thermal stability of Ti1-xA1xN films. The results show that the phase transformations are initiated at lower temperatures with increasing Al content.

National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-85660OAI: oai:DiVA.org:liu-85660DiVA: diva2:572395
Available from: 2012-11-27 Created: 2012-11-27 Last updated: 2016-08-31
In thesis
1. Thermal stability and age hardening of TiN-based thin films
Open this publication in new window or tab >>Thermal stability and age hardening of TiN-based thin films
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented herein is about characterizing phase transformations in cathodic arc plasma-deposited Ti1-xA1xN and Ti1-zZrzN thin films for cutting tool applications, and to investigate how the films' mechanical properties are affected by such transformations during thermal annealing. Post-deposition analyses were carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), nanoindentation, four-point probe sheet resistance, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and Rutherford backscattering spectrometry (RBS). For Ti1-xA1xN, residual stresses relax through annihilation of depositioninduced lattice defects in the 500-900°C regime. Stress relaxation is a multiple process with activation energies of 2.0-2.9 eV. At ~900°C, phase transformation from the as-deposited metastable single-phase [NaCl] structure into the thermodynamically stable [NaCl]-TiN and [wurtzite]-A1N proceeds through spinodal decomposition, during which [NaCl]-TiN and [NaCl]-A1N domains form from the [NaCl]-Ti1-x,A1xN matrix. Activation energies for the transformation process of 2.9-3.5 eV indicate grain boundary and defect-assisted segregation of Ti and A1. The films age harden during transformation, with an increase in film hardness from the as-deposited condition of ~35 GPa to ~36-37 GPa following post-deposition annealing at 900°C, while pure TiN softens to ~20 GPa. Hardening originates from coherency strains due to lattice-mismatch between [NaCl]-structure TiN and AIN domains formed during initial stages of spinodal decomposition. Ti1-xA1xN-coated cutting tools can therefore be said to 'adapt' to the high temperatures and cutting forces encountered during in-service machining operations. For Ti1-zZrzN, calculations on phase stabilities using density-functional theory (OFT) show that the pseudo-binary system exhibits a miscibility gap. Thus, there is a driving force for transformation from the as-deposited metastable single-phase [NaCl] structure into [NaCl]-structure TiN and ZrN components. For such compositions, an essentially retained film hardness after post-deposition annealing at 1100-1200°C has been observed. The principal hardening mechanism for this particular nitride thin film system is proposed to be solid-solution hardening through localized lattice strain fields originating from difference in atomic radius of Ti and Zr. Finally, single-crystal Ti2A1N thin films belonging to the so-called MAX-phase class of materials have been successfully synthesized by reactive magnetron sputtering. The results are promising for the prospects of synthesizing a range of MAX-phase nitride materials as single-crystal thin films and polycrystalline coatings.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. 68 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 922
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-28396 (URN)13532 (Local ID)91-852-9728-3 (ISBN)13532 (Archive number)13532 (OAI)
Public defence
2005-02-25, Planck, Fysikhuset, Campus Valla, Linköpings Universitet, Linköping, 10:15 (English)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-11-27Bibliographically approved

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Hörling, AndersHultman, Lars

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