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Thermal stability and age hardening of TiN-based thin films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-28396Local ID: 13532ISBN: 91-852-9728-3 (print)OAI: oai:DiVA.org:liu-28396DiVA: diva2:249202
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
List of papers
1. Thermal stability of arc evaporated high aluminum-content Ti1−xAlxN thin films
Open this publication in new window or tab >>Thermal stability of arc evaporated high aluminum-content Ti1−xAlxN thin films
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2002 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 20, no 5, 1815-1823 p.Article in journal (Refereed) Published
Abstract [en]

The thermal stability of Ti1−xAlxN films deposited by arc evaporation from Ti–Al cathodes with 67 and 75 at. % aluminum, respectively, has been investigated. The microstructure of as-deposited and isothermally annealed samples were studied using scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The chemical composition and elemental distribution were determined by energy dispersive x ray (EDX), Rutherford backscattering spectrometry, and EDX mapping. Transmission electron micrographs revealed a dense and columnar microstructure in the as-deposited condition. Films deposited from the 67 at. % cathodes were of cubic NaCl-structure phase, whereas films deposited from the 75 at. % cathodes exhibited nanocrystallites of wurzite-structure hexagonal-phase AlN in a cubic (c)-(Ti,Al)N matrix. Both films were stable during annealing at 900 °C/120 min with respect to phase composition and grain size. Annealing at 1100 °C of films deposited from the 67 at. % cathodes resulted in phase separation of c-TiN and h-AlN, via spinodal decomposition of c-TiN and c-AlN. (Ti,Al)N films undergo extensive stress relaxation and defect annihilation at relatively high temperatures, and aspects of these microstructural transformations are discussed.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-18801 (URN)10.1116/1.1503784 (DOI)
Available from: 2009-06-08 Created: 2009-06-04 Last updated: 2017-12-13Bibliographically approved
2. Mechanical properties and machining performance of Ti1−xAlxN-coated cutting tools
Open this publication in new window or tab >>Mechanical properties and machining performance of Ti1−xAlxN-coated cutting tools
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2005 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 191, no 2-3, 384-392 p.Article in journal (Refereed) Published
Abstract [en]

The mechanical properties and machining performance of Ti1−xAlxN-coated cutting tools have been investigated. Processing by arc evaporation using cathodes with a range of compositions was performed to obtain coatings with compositions x=0, x=0.25, x=0.33, x=0.50, x=0.66 and x=0.74. As-deposited coatings with x≤0.66 had metastable cubic structures, whereas x=0.74 yielded two-phase coatings consisting of cubic and hexagonal structures. The as-deposited and isothermally annealed coatings were characterised by nanoindentation, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Cutting tests revealing tool wear mechanisms were also performed. Results show that the Al content, x, promotes a (200) preferred crystallographic orientation and has a large influence on the hardness of as-deposited coatings. The high hardness (∼37 GPa) and texture of the as-deposited Ti1−xAlxN coatings are retained for annealing temperatures up to 950 °C, which indicates a superior stability of this system compared to TiN and Ti(C,N) coatings. We propose that competing mechanisms are responsible for the effectively constant hardness: softening by residual stress relaxation through lattice defect annihilation is balanced by hardening from formation of a coherent nanocomposite structure of c-TiN and c-AlN domains by spinodal decomposition. This example of secondary-phase transformation (age-) hardening is proposed as a new route for advanced surface engineering, and for the development of future generation hard coatings.

Keyword
Hard coatings; TiAlN; Age hardening; Spinodal decomposition; Transition; Metal nitrides
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-18823 (URN)10.1016/j.surfcoat.2004.04.056 (DOI)
Available from: 2009-06-08 Created: 2009-06-05 Last updated: 2017-12-13Bibliographically approved
3. Phase transformations in Ti1xA1xN thin films
Open this publication in new window or tab >>Phase transformations in Ti1xA1xN thin films
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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:nbn:se:liu:diva-85660 (URN)
Available from: 2012-11-27 Created: 2012-11-27 Last updated: 2016-08-31
4. Phase stability and structural properties of Ti1-zZrzN (0<z<1) thin films
Open this publication in new window or tab >>Phase stability and structural properties of Ti1-zZrzN (0<z<1) thin films
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Single-phase [NaCl]-structure Ti1-zZrzN thin films (0<z<1) have been deposited using cathodic arc plasma deposition. The films were investigated using X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and nanoindentation. Theoretical calculations on phase stabilities using density-functional theory revealed that the pseudo-binary TiN-ZrN system exhibits a miscibility gap, with respect to phase transformation from the as-deposited single-phase [NaCl] structure into [NaCl]-strueture TiN and ZrN components up to 980°C for z=0.35. The films were found to retain their as-deposited single-phase [NaCl] structure during post-deposition annealing for 120 min at 600, 700, 1100 and 1200°C, and for as long as 195 h at 600°C. This effective thermal stability is explained by a limited driving force for phase transformation and insufficient atom diffusivity. For two film compositions deepest within the miscibility gap, however, results from nanoindentation show an essentially retained hardness at ~30 GPa after annealing at 1100-1200°C. The principal hardening mechanism for the Ti1-zZrzN fihns is thus proposed to be solid-solution hardening through localized lattice strain fields originating from difference in atomic radius of Ti and Zr. This particular system offers interesting opportunities for fundamental studies of time-temperature-transformations of ternary nitride thin films.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85661 (URN)
Available from: 2012-11-27 Created: 2012-11-27 Last updated: 2016-08-31
5. Single-crystal Ti2AlN thin films
Open this publication in new window or tab >>Single-crystal Ti2AlN thin films
2005 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 11, 111913- p.Article in journal (Refereed) Published
Abstract [en]

We have produced pure thin-film single-crystal Ti2AlN(0001), a member of the Mn+1AXn class of materials. The method used was UHV dc reactive magnetron sputtering from a 2Ti:Al compound target in a mixed Ar–N2 discharge onto (111) oriented MgO substrates. X-ray diffraction and transmission electron microscopy were used to establish the hexagonal crystal structure with c and a lattice parameters of 13.6 and 3.07 Å, respectively. The hardness H, and elastic modulus E, as determined by nanoindentation measurements, were found to be 16.1±1 GPa and 270±20 GPa, respectively. A room-temperature resistivity for the films of 39 μΩ cm was obtained.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-45490 (URN)10.1063/1.1882752 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13

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