Chapter 18. The Effects of Load, Grain Size, and Grain Boundaries on the Hardness of Alumina

  1. Don Bray
  1. Andreas Krell

Published Online: 23 MAR 2010

DOI: 10.1002/9780470294499.ch18

22nd Annual Conference on Composites, Advanced Ceramics, Materials, and Structures: B: Ceramic Engineering and Science Proceedings, Volume 19, Issue 4

22nd Annual Conference on Composites, Advanced Ceramics, Materials, and Structures: B: Ceramic Engineering and Science Proceedings, Volume 19, Issue 4

How to Cite

Krell, A. (1998) The Effects of Load, Grain Size, and Grain Boundaries on the Hardness of Alumina, in 22nd Annual Conference on Composites, Advanced Ceramics, Materials, and Structures: B: Ceramic Engineering and Science Proceedings, Volume 19, Issue 4 (ed D. Bray), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470294499.ch18

Author Information

  1. Fraunhofer-Institute for Ceramic Technologies and Sintered Materials, D-01277 Dresden Germany

Publication History

  1. Published Online: 23 MAR 2010
  2. Published Print: 1 JAN 1998

ISBN Information

Print ISBN: 9780470375594

Online ISBN: 9780470294499

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Keywords:

  • petrography;
  • elimination;
  • devitrification;
  • crystalline substance's;
  • X-ray diffraction

Summary

A model describes the load (size) effect in hardness assuming an increasing microplasticity when for the extension of the plastic zone growth and multiplication of pre-existing dislocations are more effective than the generation of new lattice defects in the surrounding virgin material. If similar scale limitations for the microplastic deformation apply in polycrystals due to small grain sizes as in singl crystals at small plastic zone sizes (small loads), the size effect in sapphire is analogous to the grain size effect of the polycrystalline material: in sapphire the hardness depends on a changing microplasticity associated with known sizes of the plastic zone in the same way as it depends, in sintered alumina, on the grain size. Contrary to the size effect in sapphire, however, the grain size effect in polycrystals includes grain boundary contributions to the deformation. A large hardness difference is observed in plastically deformed volumes of sapphire and in sintered alumina with grains of the same size. This difference reveals substantial inelastic grain boundary deformation at room temperature even for coarser microstructures.