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Phase Transformations in Face Centered Cubic (Al,Cr)2O3 Thin Films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2012 (English)Conference paper, Presentation (Other academic)
Abstract [en]

Face centered cubic (Al1-xCrx)2O3 solid solution films, with x in the range 0.60<x<0.70, have been deposited using dual reactive RF magnetron sputtering from Al and Cr targets in mixed Ar/O2 discharge at a substrate temperature of 500 °C. The films have a strong <100> preferred orientation. The unit cell parameter is 4.04 Å determined by x-ray diffraction and high resolution transmission electron microscopy techniques. Nanoindentation shows that the films exhibit hardness values up to 26 GPa and reduced modulus of 220-235 GPa. In the present work, ex-situ annealing studies were performed on as-deposited samples for a series of temperatures up to 1000 °C and annealing time of 0-8 h. The fcc structure remains intact up to 700 °C. The onset of phase transformation from fcc to corundum is observed in the sample annealed at 900 °C for 2 h, where annealing for 2 h at 1000 °C results in complete transformation to a-(Al1-xCrx)2O3. There is no indication of any phase separation into a-Cr2O3 and Al2O3 prior and after the annealing, confirmed by the in-plane and out-of-plane line scans performed in EDX TEM and long-time small step size q/2q XRD patterns. The kinetics of phase transformation studied by the Jahnson-Avrami-Mehl model shows the apparent activation energy of the phase transformation process in the range of 380-480 kJ/mol. Ongoing work is focused on theoretical studies of the stability and composition of the structure of the as-deposited fcc-(Al1-xCrx)2O3 solid solution films, which are suggested to have a non-stoichiometric NaCl structure with 33% vacancy occupancy on Al/Cr sites.

Place, publisher, year, edition, pages
National Category
Manufacturing, Surface and Joining Technology Physical Sciences
URN: urn:nbn:se:liu:diva-84381OAI: diva2:558848
39th International Conference on Metallurgical Coatings and Thin Films (ICMCTF), 23-27 April 2012, San Diego, USA
Available from: 2012-10-05 Created: 2012-10-05 Last updated: 2013-01-21
In thesis
1. Growth and Heat Treatment Studies of Al-Cr-O and Al-Cr-O-N Thin Films
Open this publication in new window or tab >>Growth and Heat Treatment Studies of Al-Cr-O and Al-Cr-O-N Thin Films
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aluminum oxide based thin films are applied on cutting tool inserts as a top layer to protect the underlying nitride or carbide functional layer from the harsh working environment in terms of abrasive and chemical wear under thermal and pressure load. This Thesis explores the synthesis and characterization of the next generations of multifunctional wear-resistant thin film coatings in the form of Al-Cr-O and Al-Cr-O-N compounds. The experiments include the deposition of oxide films by reactive magnetron sputtering and cathodic arc evaporation as well as investigation of structural and mechanical properties in as-deposited and annealed states. Ternary (Al1-xCrx)2+yO3-y films were deposited on Si(001) and WC-Co substrates kept at 400-575 °C from elemental Al and Cr or alloyed Al/Cr cathodes in Ar/O2, O2/N2, and pure O2 atmospheres. Also, quaternary (Al1-xCrx)2+z(O1-yNy)3-z films were deposited at substrate temperature of ~400 °C on WC-Co substrates in O2/N2 atmosphere. X-ray diffraction and analytical electron microscopy combined with ab initio calculations showed the existence of a new face centered cubic (Al,Cr)2O3 phase with 33% vacancies on the metallic Al/Cr sites. Increasing the temperature during annealing of these metastable cubic films resulted in phase transformation to corundum solid solution in the temperature range of 900-1100 °C. The apparent activation energy of this phase transformation process was calculated as 380-480 kJ/mol by using the Johnson-Mehl-Avrami model. The mechanical properties of the cubic and corundum oxide films were measured in terms of nanoindentation hardness and metal cutting performance. The cubic and corundum films showed hardness values of 26-28 GPa and 28-30 GPa, respectively. The oxynitride solid solution films showed to be predominantly cubic Al-Cr-N and cubic-(Al,Cr)2O3 and secondary corundum-(Al,Cr)2O3 with a hardness of ~30 GPa, slightly higher than Al-rich ternary oxides. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 79 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1497
National Category
Natural Sciences
urn:nbn:se:liu:diva-87668 (URN)978-91-7519-710-4 (ISBN)
Public defence
2013-02-12, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2013-01-21Bibliographically approved

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