Microstructural evolution and properties of nanocrystalline alumina made by reactive sputtering deposition

  • Chou T
  • Adamson D
  • Mardinly J
 et al. 
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Nanocrystalline aluminum oxide films have been synthesized by r.f. reactivesputtering deposition, and their structure and properties have been studied by grazing angle X-ray diffraction, nanoindentation and transmission electron microscopy. The as-deposited films contained nanocrystalline γ-Al2O3embedded in an amorphous Al2O3matrix. Annealing of the films between 800 and 1200°C resulted in crystallization of the amorphousAl2O3matrix. various degrees of γ→α phase transformation. Prolonged anneals of the films at 800 °C for 24h gave arise to the development of structural texture in γ-Al2O3grains. No appreciable grain growth of γ-Al2O3was detected in the films annealed at temperatures below 1200°C. Annealing of the films at 1200°C for 2 h resulted in the formation of explosively grown, single-crytsal α-Al2O2grains in a highly textured, polycrystalline γ-Al2O3matrix. The microstructure of γ-Al2O3exhibited an intriguing layered characteristic. These layers were aligned consistently throughout the films; most of them were oriented at 90° to each other. The layered microstructure is believed to be the characteristic of an intermediate state during γ→α transformation, which contributes to the concurrent explosive grain growth of α-Al2O3. The nucleation of γ-Al2O3is suggested to occur along the {220} crystallographic planes of γ-Al2O3.Preliminary micromechanical properties of as-deposited nanocrystalline Al2O3films are reported. © 1991.

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  • T. C. Chou

  • D. Adamson

  • J. Mardinly

  • T. G. Nieh

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