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Anisotropy effects onmicrostructure and properties in decomposed arc evaporated Ti1-xAlxN coatings during metal cutting
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology. Seco Tools AB, Fagersta, Sweden.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
Seco Tools AB, Fagersta, Sweden.
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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. Vol. 235, no 25, 181-185 p.
Keyword [en]
Cathodic arc evaporation; TiAlN; Anisotropy; Microstructure; Hardness; Metal cutting
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-96400DOI: 10.1016/j.surfcoat.2013.07.031ISI: 000329596100022OAI: oai:DiVA.org:liu-96400DiVA: diva2:641613
Funder
Vinnova
Available from: 2013-08-19 Created: 2013-08-19 Last updated: 2017-12-06
In thesis
1. Microstructural evolution of TiAlN hard coatings at elevated pressures and temperatures
Open this publication in new window or tab >>Microstructural evolution of TiAlN hard coatings at elevated pressures and temperatures
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:nbn:se:liu:diva-106507 (URN)10.3384/diss.diva-106507 (DOI)978-91-7519-372-4 (ISBN)
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

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Norrby, NiklasUllbrand, JenniferOdén, Magnus

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