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Thermal shock of porous silicon nitride with preferentially aligned grains
Published online by Cambridge University Press: 31 January 2011
Abstract
We studied the thermal shock resistance of a silicon nitride containing elongated and preferentially aligned grains with different volume fractions of pores, ranging from 0 to 0.27. It was found that an increase in the volume fraction of pores decreased both the strength and the temperature through which the sample must be quenched to cause cracking. However, at intermediate values of the porosity (0.07), the temperature change required to cause cracking was much smaller than predicted. Observations of the resulting damage suggested that this had occurred because of the formation of cracks just underneath and parallel to the cooled surface of the sample that were able to change the direction of their growth. The extent of cracking was found to be only very weakly dependent on the volume fraction of pores, consistent with calculations of the variation of crack driving force within the sample.
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