Phase Transformations in Face Centered Cubic (Al,Cr)2O3 Thin Films
2012 (English)Conference paper, Presentation (Other academic)
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
Manufacturing, Surface and Joining Technology Physical Sciences
IdentifiersURN: urn:nbn:se:liu:diva-84381OAI: oai:DiVA.org:liu-84381DiVA: diva2:558848
39th International Conference on Metallurgical Coatings and Thin Films (ICMCTF), 23-27 April 2012, San Diego, USA