The effect of grain shape on strength variability of alumina ceramics

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Fine-grained and coarse-grained aluminas containing either equiaxed or elongated grain structures were fabricated from commercial-purity and high-purity alumina powders. Compared to the high-purity aluminas, the commercial-purity aluminas having a coarse grain size and elongated grain structures exhibited significantly more pronounced flaw tolerance and T-curve behavior. T-curve behavior determined from indentation strength tests suggested that only the coarse- grained, elongated-grain alumina had a T-curve sufficient to cause stable crack extension prior to failure, a requirement for any observable improvement in reliability. In the high-purity aluminas as well as the fine-grained commercial-purity aluminas, however, it is likely that little or no stable ... continued below

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20 p.

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Readey, M.J. October 1, 1995.

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  • Sandia National Laboratories
    Publisher Info: Sandia National Labs., Albuquerque, NM (United States)
    Place of Publication: Albuquerque, New Mexico

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Fine-grained and coarse-grained aluminas containing either equiaxed or elongated grain structures were fabricated from commercial-purity and high-purity alumina powders. Compared to the high-purity aluminas, the commercial-purity aluminas having a coarse grain size and elongated grain structures exhibited significantly more pronounced flaw tolerance and T-curve behavior. T-curve behavior determined from indentation strength tests suggested that only the coarse- grained, elongated-grain alumina had a T-curve sufficient to cause stable crack extension prior to failure, a requirement for any observable improvement in reliability. In the high-purity aluminas as well as the fine-grained commercial-purity aluminas, however, it is likely that little or no stable extension occurs prior failure, suggesting that strength in these materials is dependent on the critical flaw size. Strength tests on polished specimens showed the commercial-purity aluminas had a lower means strength than the high- purity aluminas and the coarse-grained aluminas exhibited a lower mean strength compared to the fine-grained aluminas. An analysis of the mean strength versus grain size revealed that the differences in critical flaw size alone could not account for the differences in mean strength. Instead, a combination of changes in flaw size as well as T-curve behavior were shown to be responsible for the differences in strength and flaw tolerance. T-curve behavior was also found to have a profound influence on the strength variability of alumina. For example, the Weibull modulus for the coarse-grained, commercial- purity alumina was almost twice that of the fine-grained, high-purity material. Tests with indented specimens conclusively demonstrated that improvements in reliability in these materials are not due solely to changes in the critical flaw size distribution but rather a combination of flaw size distribution and T-curve behavior.

Physical Description

20 p.

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OSTI as DE96000698

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  • 6. international symposium on fracture mechanics of ceramics, Karlsruhe (Germany), 18-20 Jul 1995

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  • Other: DE96000698
  • Report No.: SAND--95-2192C
  • Report No.: CONF-950713--1
  • Grant Number: AC04-94AL85000
  • Office of Scientific & Technical Information Report Number: 106727
  • Archival Resource Key: ark:/67531/metadc624227

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  • October 1, 1995

Added to The UNT Digital Library

  • June 16, 2015, 7:43 a.m.

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  • June 22, 2016, 7:07 p.m.

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Readey, M.J. The effect of grain shape on strength variability of alumina ceramics, article, October 1, 1995; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc624227/: accessed April 26, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.