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Effect of Inclusions on Densification: I, Microstructural Development in an Al 2 O 3 Matrix Containing a High Volume Fraction of ZrO 2 Inclusions
Author(s) -
Sudre Olivier,
Lange Fred F.
Publication year - 1992
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.1151-2916.1992.tb07836.x
Subject(s) - materials science , microstructure , slurry , composite material , volume fraction , composite number , matrix (chemical analysis) , volume (thermodynamics) , mineralogy , thermodynamics , geology , physics
The microstructural changes produced by large (38 to 53 μ m), single‐crystal ZrO 2 inclusions (0, 0.09, 0.30 volume fractions, based on solid volume) within an Al 2 O 3 powder matrix were detailed as a function of constrained densification. Composite powder compacts were produced by pressure filtration for conditions where the Al 2 O 3 slurry was either flocced or dispersed. For both conditions, the ZrO 2 inclusions constrained densification. Microstructural observations for all composites revealed (1) the presence of cracks with large opening displacements between inclusions and (2) large density variations within the matrix. The cracks were most frequent at high volume fraction of inclusions in composites produced from flocced slurries and apparently originated during specimen preparation. Their large opening displacment was a result of matrix densification. Fewer cracks were observed in composites produced from dispersed slurries. Instead, these microstructures were dominated by large variations in matrix density, viz., dense regions surrounding low‐density regions, not consitent with the initial packing density of the matrix powder. The denser regions were formed early in the densification schedule. The lower‐density regions eventually developed into regions containing large, elongated voids as the Al 2 O 3 matrix grains became larger with heat‐treatment time. This pore enlargement process was shown to result from the disappearance of necks between originally sintered grains and appeared similar to the thermodynamic instability observed in thin films and constrained fibers.