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Growth and Heat Treatment Studies of Al-Cr-O and Al-Cr-O-N Thin Films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1497
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-87668ISBN: 978-91-7519-710-4 (print)OAI: oai:DiVA.org:liu-87668DiVA: diva2:592995
Public defence
2013-02-12, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Face-Centered Cubic (Al1-xCrx)2O3
Open this publication in new window or tab >>Face-Centered Cubic (Al1-xCrx)2O3
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2011 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 8, 2426-2429 p.Article in journal (Refereed) Published
Abstract [en]

We report the discovery of a face-centered cubic (Al1−xCrx)2O3 solid solution [0.60bxb0.70] in films grownonto Si substrates using reactive radio frequency magnetron sputtering from Al and Cr targets at 400 °C. Theproposed structure is NaCl-like with 33% vacancies on the metal sites. The unit cell parameter is 4.04 Å asdetermined by X-ray diffraction. The films have a b100N preferred crystallographic orientation and exhibithardness values up to 26 GPa and an elastic modulus of 220–235 GPa.

Place, publisher, year, edition, pages
Elsevier, 2011
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-65698 (URN)10.1016/j.tsf.2010.11.052 (DOI)000287631500008 ()
Funder
Swedish Research Council
Note
Original Publication: Ali Khatibi, Justinas Palisaitis, Carina Höglund, Anders Eriksson, Per O. Å. Persson, Jens Jensen, Jens Birch, Per Eklund and Lars Hultman, Face-Centered Cubic (Al1-xCrx)2O3 , 2011, Thin Solid Films, (519), 2426-2429. http://dx.doi.org/10.1016/j.tsf.2010.11.052 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2011-02-21 Created: 2011-02-17 Last updated: 2017-12-11Bibliographically approved
2. Phase Transformations in Face Centered Cubic (Al,Cr)2O3 Thin Films
Open this publication in new window or tab >>Phase Transformations in Face Centered Cubic (Al,Cr)2O3 Thin Films
2012 (English)Conference paper, Oral presentation only (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.

National Category
Manufacturing, Surface and Joining Technology Physical Sciences
Identifiers
urn:nbn:se:liu:diva-84381 (URN)
Conference
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
3. Structural and mechanical properties of Cr-Al-O-N thin films grown by cathodic arc deposition
Open this publication in new window or tab >>Structural and mechanical properties of Cr-Al-O-N thin films grown by cathodic arc deposition
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2012 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 19, 6494-6507 p.Article in journal (Refereed) Published
Abstract [en]

Coatings of (CrxAl1-x)(delta)(O1-yNy)(xi) with 0.33 less than= x less than= 0.96, 0 less than= y less than= 1 and 0.63 less than= delta/xi less than= 1.30 were deposited using cathodic arc evaporation in N-2/O-2 reactive gas mixtures on 50 V negatively biased WC-10 wt.% Co substrates from different Cr and Al alloys with three different Cr/Al compositional ratios. For N-2 less than 63% of the total gas, ternary (Cr,Al)(2)O-3 films containing less than1 at.% of N forms; as determined by elastic recoil detection analysis. Increasing the N-2 fraction to 75% and above results in formation of quaternary oxynitride films. Phase analyses of the films by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy show the predominance of cubic Cr-Al-N and cubic-(Cr,Al)(2)O-3 solid solutions and secondary hexagonal alpha-(Cr,Al)(2)O-3 solid solution. High Cr and Al contents result in films with higher roughness, while high N and O contents result in smoother surfaces. Nanoindentation hardness measurements showed that Al-rich oxide or nitride films have hardness values of 24-28 GPa, whereas the oxynitride films have a hardness of similar to 30 GPa, regardless of the Cr and Al contents. 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
Elsevier, 2012
Keyword
Physical vapor deposition; Solid solution; Face-centered cubic crystals; Alumina (alpha-Al2O3); Oxynitride
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87218 (URN)10.1016/j.actamat.2012.08.010 (DOI)000311188400006 ()
Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2017-12-06
4. Structural and Mechanical Properties of (AlxCr1-x)2+yO3-y Coatings Grown by Reactive Cathodic Arc Evaporation in As-deposited and Annealed States
Open this publication in new window or tab >>Structural and Mechanical Properties of (AlxCr1-x)2+yO3-y Coatings Grown by Reactive Cathodic Arc Evaporation in As-deposited and Annealed States
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2013 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 61, no 13, 4811-4822 p.Article in journal (Refereed) Published
Abstract [en]

Coatings of (AlxCr1-x)2+yO3-y with 0.51≤x≤0.84 and 0.1≤y≤0.5 were deposited on hard cemented carbides substrates in an industrial cathodic arc evaporation system from powder-metallurgy prepared Cr/Al targets in pure O2 and O2+N2 atmospheres. The substrate temperature and bias in all the deposition runs were 575 °C and -120 V, respectively. The composition of the coatings measured by energy dispersive x-ray spectroscopy and elastic recoil detection analysis was the same as that of the targets. Microstructure analyses performed by symmetrical X-ray diffraction and transmission electron microscopy showed that corundum, cubic or mixed-phase coatings formed depending on the Cr/Al ratio of the coatings and O2 flow per activetarget during deposition. The corundum phase was promoted by high Cr content and high O2 flow per target, while the cubic phase was mostly observed for high Al content and low O2 flow per active target. In situ annealing of the cubic coatings resulted in phase transformation from cubic to corundum completed in the temperature range of 900-1100 °C, while corundum coatings retained their structure in the same range of annealing temperatures. Nanoindentation hardness of the coatings with Cr/Al ratio < 0.4 was 26-28 GPa, regardless of the structure. Increasing the Cr content of the coatings resulted in increased hardness of 28-30 GPa for corundum coatings. Wear resistance testing in a turning operation showed that coatings of Al-Cr-O have improved resistance to crater wear at the cost of flank wear compared to TiAlN coatings.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Physical vapor deposition (PVD); Ternary alloys; Alumina (α-Al2O3); Solid solution; Al-Cr-O alloys
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-87666 (URN)10.1016/j.actamat.2013.05.002 (DOI)000321601400011 ()
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2017-12-06Bibliographically approved
5. Theoretical investigation of cubic B1-like and corundum (Cr1−xAlx)2O3 solid solutions
Open this publication in new window or tab >>Theoretical investigation of cubic B1-like and corundum (Cr1−xAlx)2O3 solid solutions
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

First-principles calculations are employed to investigate the stability and properties of cubic rock-salt like (Cr1−xAlx)2O3 solid solutions, stabilized by metal site vacancies as recently reported experimentally. It is demonstrated that the metal site vacancies can indeed be ordered in a way that gives rise to a favorable coordination of all O atoms in the lattice. B1-like structures with ordered and disordered metal site vacancies are studied for (Cr0.5Al0.5)2O3 and found to a have cubic lattice spacing close to the values reported experimentally, in contrast to fluorite-like and perovskite structures. The obtained B1-like structures are higher in energy than corundum solid solutions for all compositions, but with an energy offset per atom similar to other metastable systems possible to synthesize with physical vapor deposition techniques. The obtained electronic structures show that the B1-like systems are semiconducting although with smaller band gaps than the corundum structure.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-87667 (URN)
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2016-08-31Bibliographically approved

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