Internal Strain Measurements and X-ray Imaging in Interpenetrating-Phase Al 2 O 3 /Al Composites
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Internal Strain Measurements and X-ray Imaging in Interpenetrating-Phase Al2O3/Al Composites Marcus L. Young1,2, Jon D. Almer2, Ulrich Lienert2, Kamel Fezzaa2, Wah-Keat Lee2, Dean R. Haeffner2, and David C. Dunand1 1 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, U.S.A. 2 Advanced Photon Source, Argonne National Laboratory Argonne, Illinois 60439, U.S.A. ABSTRACT Interpenetrating Al2O3/Al composites were created by liquid-metal infiltration of alumina preforms with three-dimensional periodicity produced by a robotic deposition method. Volume-averaged lattice strains in the alumina phase were measured by synchrotron x-ray diffraction at various uniaxial compression stresses up to 350 MPa. Load transfer, which is experimentally found to occur between the aluminum and the alumina phase, is in agreement with simple rule of mixtures models. Spatially resolved measurements showed variations in load transfer at different positions within the composite for the elastic-, plastic-, and damage-deformation regimes. Using phaseenhanced imaging, the extent of damage within the composites was observed.
INTRODUCTION Interpenetrating phase composites (IPCs) are characterized by two co-continuous and percolating phases. Ceramic-metal IPCs typically exhibit much higher toughness than pure ceramics, e.g., cermets such as WC-Co with high-metal content. Several liquidmetal processing routes exist for creating Al2O3-Al IPCs, including infiltration of porous Al2O3 preforms [1], reactive metal penetration [2], and displacement reactions [3]. Ceramic-metal IPCs with a highly regular architecture and tailored properties can be fabricated from a number of techniques involving solid freeform ceramic preforms with complex three-dimensional (3-D) ceramic architectures. One direct-write technique, known as robocasting, can be used to create the aforementioned preforms by extruding colloidal inks in a layer-wise fashion [4-6]. Here, we study the mechanical properties of such an Al2O3-Al IPC. EXPERIMENTAL DETAILS As described in more detail previously [7, 8], Al2O3 preforms with a regular 0/90 architecture were produced by robotic deposition using a gel-based ink (with 5 vol% ZrO2 as sintering aid). The first layer is composed of a series of equidistant rods (250 µm in diameter) parallel to the x-axis with “hairpins” connecting them. The second layer is identical to the first but rotated by 90 degrees, i.e., is parallel to the y-axis. This process was repeated 15 times, resulting in a 30-layer preform with simple-cubic symmetry.
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Alternatively, by offsetting every other layer by one rod diameter, a face-centered-cubic symmetry preform was created. Sintered Al2O3 preforms were gas-pressure, liquid-metal infiltrated with either 99.99% pure aluminum or aluminum alloy 7075, as described in detail previously [8, 9]. The resulting composites were machined to 5.2x5.2x9.9 mm3 parallelepipeds with the ceramic preform remaining completely incased within aluminum. The pure aluminum matrix
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