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Microstructural evolution of TiAlN hard coatings at elevated pressures and temperatures
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A typical hard coating on metal cutting inserts used in for example turning, milling or drilling operations is TiAlN. At elevated temperatures, TiAlN exhibits a well characterized spinodal decomposition into coherent cubic TiN and AlN rich domains, which is followed by a transformation from cubic to hexagonal AlN. Using in-situ synchrotron x-ray radiation, the kinetics of the second transformation was investigated in this thesis and the strong temperature dependence on the transformation rate indicated a diffusion based nucleation and growth mechanism. The results gave additional information regarding activation energy of the transformation and the critical wavelength of the cubic domains at the onset of hexagonal AlN. After nucleation and growth, the hexagonal domains showed a striking resemblance with the preexisting cubic AlN microstructure.

During metal cutting, the tool protecting coating is subjected to temperatures of ~900 ºC and pressure levels in the GPa range. The results in this thesis have shown a twofold effect of the pressure on the decomposition steps. Firstly, the spinodal decomposition was promoted by the applied pressure during metal cutting which was shown by comparisons with annealed samples at similar temperatures. Secondly, the detrimental transformation from cubic to hexagonal AlN was shown to be suppressed at elevated hydrostatic pressures. A theoretical pressure/temperature phase diagram, validated with experimental results, also showed suppression of hexagonal AlN by an increased temperature at elevated pressures.

The spinodal decomposition during annealing and metal cutting was in this work also shown to be strongly affected by the elastic anisotropy of TiAlN, where the phase separation was aligned along the elastically softer <100> directions in the crystal. The presence of the anisotropic microstructure enhanced the mechanical properties compared to the isotropic case, mainly due to a shorter distance between the c-AlN and c-TiN domains in the anisotropic case. Further improvement of the metal cutting behavior was realized by depositing individual layers with an alternating bias. The individual bias layers exhibited microstructural differences with different residual stress states. The results of the metal cutting tests showed an enhanced wear resistance in terms of both crater and flank wear compared to coatings deposited with a fixed bias.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 75 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1583
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-106507DOI: 10.3384/diss.diva-106507ISBN: 978-91-7519-372-4 (print)OAI: oai:DiVA.org:liu-106507DiVA: diva2:716472
Public defence
2014-06-11, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-05-09 Created: 2014-05-09 Last updated: 2014-05-09Bibliographically approved
List of papers
1. Pressure and temperature effects on the decomposition of arc evaporated Ti0.6Al0.4N coatings during metal cutting
Open this publication in new window or tab >>Pressure and temperature effects on the decomposition of arc evaporated Ti0.6Al0.4N coatings during metal cutting
2012 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 209, 203-207 p.Article in journal (Refereed) Published
Abstract [en]

The isostructural decomposition of arc evaporated Ti0.6Al0.4N coatings at the elevated temperatures and high stresses occurring during metal cutting have been studied. Comparisons are made with short time (t=10 min) anneals at temperatures typical for steel turning operations. The evolution of the decomposed domain sizes are studied by analytical transmission electron microscopy from samples originating from the rake face. Temperature and force measurements during turning allowed for separation of the effects of the temperature and stresses on domain size evolution. The results show a peak temperature of around 900 °C and a peak normal stress of around 2 GPa during cutting. The overall domain size is larger after cutting compared to the annealed sample at the same temperature. The results suggest that pressures generated during cutting promote coherent isostructural decomposition which is in line with theoretical studies but for considerably higher pressures.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-78825 (URN)10.1016/j.surfcoat.2012.08.068 (DOI)000310656200029 ()
Note

Funding Agencies|Swedish Foundation for Strategic Research (SSF) project Designed Multicomponent Coatings, Multifilms||

Available from: 2012-06-21 Created: 2012-06-21 Last updated: 2017-12-07Bibliographically approved
2. High pressure and high temperature stabilization of cubic AlN in Ti0.60Al0.40N
Open this publication in new window or tab >>High pressure and high temperature stabilization of cubic AlN in Ti0.60Al0.40N
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2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 5Article in journal (Refereed) Published
Abstract [en]

In the present work, the decomposition of unstable arc evaporated Ti0.6Al0.4N at elevated temperatures and quasihydrostatic pressures has been studied both experimentally and by first-principles calculations. High pressure and high temperature (HPHT) treatment of the samples was realized using the multi anvil press and diamond anvil cell techniques. The products of the HPHT treatment of Ti0.6Al0.4N were investigated using x-ray diffractometry and transmission electron microscopy. Complimentary calculations show that both hydrostatic pressure and high temperature stabilize the cubic phase of AlN, which is one of the decomposition products of Ti0.6Al0.4N. This is in agreement with the experimental results which in addition suggest that the presence of Ti in the system serves to increase the stability region of the cubic c-AlN phase. The results are industrially important as they show that Ti0.6Al0.4N coatings on cutting inserts do not deteriorate faster under pressure due to the cubic AlN to hexagonal AlN transformation.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-90201 (URN)10.1063/1.4790800 (DOI)000314746200028 ()
Note

Funding Agencies|Swedish Foundation for Strategic Research (SSF)||German Research Foundation (DFG)|SPP 1236|

On the day of the defence day the status of this articla was Manucsript and title of this was High pressure and high temperature behavior of Ti0.60Al0.40N.

Available from: 2013-03-21 Created: 2013-03-21 Last updated: 2017-12-06
3. Anisotropy effects onmicrostructure and properties in decomposed arc evaporated Ti1-xAlxN coatings during metal cutting
Open this publication in new window or tab >>Anisotropy effects onmicrostructure and properties in decomposed arc evaporated Ti1-xAlxN coatings during metal cutting
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2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 235, no 25, 181-185 p.Article in journal (Refereed) Published
Abstract [en]

Anisotropy effects on the spinodal decomposition in cathodic arc evaporated cubic “phase c-Ti1−xAlxN coatingshave been studied with respect to composition, microstructure and hardness properties before and after a continuousturning operation. Coatings are simultaneously being exposed to both a high temperature and high pressureduring the metal cutting process. As evident from the current results, a high Al content coating, x = 0.66,when exposed to such extreme conditions decomposes into cubic c-AlN and c-TiN-rich domains. In this case,the evolving microstructure comprises interconnected spatially periodic, elongated and coherent cubic c-AlNand c-TiN-rich regions aligned along elastic compliant b100N crystal direction. A significantly different microstructurewith randomly oriented domains is observed for a coating with an elemental composition closer tothe isotropic limit, x = 0.28, exposed under the same conditions. From a coating hardness perspective, thenanoindentation results display a minor age hardening effect for the c-Ti1−xAlxN coating grown at x = 0.28while the coating grown with x = 0.66 exhibits a significant age-hardening effect of about 18%. We concludethat both microstructure and age hardening behavior during spinodal decomposition of c-Ti1−xAlxN correlateto the relative amount ofmetal Ti/Al ratio and consequently to the elastic anisotropy of the as-grown coatingmaterial.These results provide newinsights to the understanding of improvedwear resistance of c-Ti1−xAlxN withAl content during metal cutting.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Cathodic arc evaporation; TiAlN; Anisotropy; Microstructure; Hardness; Metal cutting
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-96400 (URN)10.1016/j.surfcoat.2013.07.031 (DOI)000329596100022 ()
Funder
Vinnova
Available from: 2013-08-19 Created: 2013-08-19 Last updated: 2017-12-06
4. Improved metal cutting performance with biasmodulated textured Ti0.50Al0.50N multilayers
Open this publication in new window or tab >>Improved metal cutting performance with biasmodulated textured Ti0.50Al0.50N multilayers
2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 257, 102-107 p.Article in journal (Refereed) Published
Abstract [en]

In this work we present the cutting performance of Ti0.50Al0.50N coatings which have been deposited with both a fixed and an alternating bias of -35 V and -70 V together with a Ti0.33Al0.67N reference coating grown at -35 V. The bias-modulated coatings were grown with different bias-layer periods, from 200 to 1200 nm. For the layers deposited with a fixed bias, a transition from a (100) to a (111) preferred orientation was observed with the change in bias from -35 V to -70 V. The coatings grown with an alternating bias, however, showed a (111) preferred orientation with an intensity that slightly depends on bias-layer period. Metal cutting performance in terms of crater and flank wear resistance show an improvement for all bias-layered coatings. This is attributed to a (111) oriented refined grain structure in combination with low residual stresses in the coating.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-106505 (URN)10.1016/j.surfcoat.2014.05.045 (DOI)000344423100013 ()
Funder
VINNOVA
Available from: 2014-05-09 Created: 2014-05-09 Last updated: 2017-12-05Bibliographically approved
5. In-situ x-ray scattering study of the cubic to hexagonal transformation of AlN in Ti1-xAlxN
Open this publication in new window or tab >>In-situ x-ray scattering study of the cubic to hexagonal transformation of AlN in Ti1-xAlxN
Show others...
2014 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 73, 205-214 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, we have studied the decomposition of arc evaporated Ti0.55Al0.45N and Ti0.36Al0.64N during heat treatment in vacuum by in-situ synchrotron wide angle x-ray scattering primarily to characterize the kinetics of the phase transformation of AlN from the cubic NaCl-structure to the hexagonal wurtzite-structure. In addition, in-situ small angle x-ray scattering measurements were conducted to explore details of the wavelength evolution of the spinodal decomposition, thus providing information about the critical size of the c-AlN rich domains prior to the onset of the h-AlN transformation. We report the fractional cubic to hexagonal transformation of AlN in Ti1-xAlxN as a function of time and extract activation energies between 320 and 350 kJ/mol dependent on alloy composition. The onset of the hexagonal transformation occurs at about 50 K lower temperature in Ti0.36Al0.64N compared to Ti0.55Al0.45N where the high Al content alloy also has a significantly higher transformation rate. A critical wavelength for the cubic domains of about 13 nm was observed for both alloys. Scanning transmission electron microscopy shows a c-TiN/h-AlN microstructure with a striking morphology resemblance to the c-TiN/c-AlN microstructure present prior to the hexagonal transformation.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-106506 (URN)10.1016/j.actamat.2014.04.014 (DOI)000337853100020 ()
Funder
VINNOVA
Note

On the day of the defence date of the thesis the status of this article was Manuscript.

Available from: 2014-05-09 Created: 2014-05-09 Last updated: 2017-12-05Bibliographically approved

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