Segregation as a driving force in the formation of nanocomposite ZrO2-Al2O3 coatings

I. Zukerman, M. Halabi, S. Hayun, R. L. Boxman, A. Raveh

Research output: Contribution to journalArticlepeer-review

Abstract

ZrO2-Al2O3 coatings were deposited on a floating substrate at a temperature of 370 °C. Various coating compositions, ranging from pure zirconia to 50 at.% alumina content, were deposited by reactive pulsed-DC magnetron sputtering using 51 mm diameter Zr and Al targets. The coating had a Zr-Al-O solid solution structure that was composed of nano-size cubic-ZrO2 grains (20 ± 5 nm) with aluminum cations distributed inside them. The deposited coatings were annealed up to 1350 °C and their structural changes were studied using Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Vickers hardness measurement. Two exothermic annealing events were observed. The first event appeared at 700–750 °C and was contributed to aluminum segregation to the grain boundaries, and the formation of a nanocomposite-ZrO2/amorphous-Al2O3 structure. The second event appeared at 1000–1200 °C and was related to coarsening (“Ostwald ripening”) of the ZrO2 grains. The coating hardness after the first event was stabilized to 19.5 ± 1.1 GPa because of the segregation, which hindered grain growth. However, after a second DSC cycle of the coating, only one sharp endothermic transformation peak was observed at onset temperature of 1060 ± 5 °C. This was associated with grain growth accompanied with zirconia transformation from the cubic to the monoclinic phase.

Original languageEnglish
Pages (from-to)28-34
Number of pages7
JournalSurface and Coatings Technology
Volume314
DOIs
StatePublished - 25 Mar 2017

Keywords

  • Hardness
  • Magnetron sputtering
  • Stabilized zirconia
  • Thermal stability
  • Thin coatings

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