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Critical Microstructures for Microcracking in Al 2 O 3 ‐ZrO 2 Composites
Author(s) -
GREEN DAVID J.
Publication year - 1982
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1982.tb09939.x
Subject(s) - materials science , volume fraction , composite material , indentation , grain size , microstructure , cubic zirconia , fracture toughness , grain boundary , elastic modulus , ceramic
The internal strains asSociated with the martensitic phase transformation of zirconia were used to introduce microcracks into Al 2 O 3 /ZrO 2 composites. The degree of transformation was found to be dependent on the volume fraction of ZrO 2 and its size, the latter of which could be controlled by suitable heat treatments. The microstructural changes that occurred during the heat treatments were studied using quantitative microscopy and X‐ray diffraction. For materials containing more than 7.5 vol% Zr0 2 , the ZrO 2 particles were found to pin the Al 2 O 3 grain boundaries, thus limiting the Al 2 O 3 grain growth. The limiting grain size was found to be dependent on size and volume fraction of ZrO 2 . Heat treatments for the higher volume fraction materials (>7.5 vol% ZrO 2 ) caused micro‐structural changes which resulted in increased amounts of monoclinic ZrO 2 at room temperature; elastic modulus measurements indicated that this was occurring concurrently with microcracking. By combining the ZrO 2 grain‐size distributions with the X‐ray analysis it was possible to calculate the critical ZrO 2 size required for the transformation. The critical size was found to decrease with increasing amounts of ZrO 2 . Hardness and indentation fracture toughness were measured on the composites. Grain fragmentation was observed at the edge of the indentations and microcracks were observed directly, using an AgNO 3 decoration technique, near the indentations.