X-ray computed micro tomography as complementary method for the characterization of activated porous ceramic preforms
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B. Grobéty Technical Mineralogy Group, Institute of Mineralogy and Petrography, University of Fribourg, CH-1700 Fribourg, Switzerland
J. Kueblera) and T. Graule EMPA, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for High Performance Ceramics, CH-8600 Duebendorf, Switzerland
L. Baumgartner Institute of Mineralogy and Petrography, Earth Science, University of Lausanne, CH-1100 Lausanne, Switzerland (Received 22 December 2006; accepted 20 February 2007)
X-ray computed micro tomography (CT) is an alternative technique to the classical methods such as mercury intrusion (MIP) and gas pycnometry (HP) to obtain the porosity, pore-size distribution, and density of porous materials. Besides the advantage of being a nondestructive method, it gives not only bulk properties, but also spatially resolved information. In the present work, uniaxially pressed porous alumina performs activated by titanium were analyzed with both the classical techniques and CT. The benefits and disadvantages of the applied measurement techniques were pointed out and discussed. With the generated data, development was proposed for an infiltration model under ideal conditions for the production of metal matrix composites (MMC) by pressureless melt infiltration of porous ceramic preforms. Therefore, the reliability of the results, received from different investigation techniques, was proved statistically and stereologically.
I. INTRODUCTION
There is an increasing interest in using metal matrix composites (MMC) in applications where materials must have properties common to both metals and ceramics, e.g., in energy technology or the automotive industry.1–4 Several methods for the fabrication of MMC materials and their properties have been proposed.5,6 An elegant and cheap way to manufacture such composites is by pressureless infiltration of metal melts into porous oxide ceramic performs.7,8 This fabrication route is, however, hampered by the nonwetting behavior of metallic liquids on most oxide ceramic surfaces.9,10 Addition of reactive elements, e.g., titanium (Ti), into the preforms has been shown to improve the wettability of
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0181 1414
J. Mater. Res., Vol. 22, No. 5, May 2007
oxide ceramics, and thus a satisfactory pressureless infiltration can be achieved.11,12 Although the mechanisms responsible for the activation are not well understood, it is obvious from preliminary experiments that the porosity and permeability of the porous performs as well as the activator particle distribution, e.g., the average distance between titanium particles, are key parameters for the infiltration process.13 A detailed knowledge of the three-dimensional (3D) assembly relating to porosity, pore-size distribution, and arrangement of the Ti particles and their size distribution within the porous ceramic performs is therefore indispensable. Mercury intrusion porosimetry (MIP), helium pycnometry (HP), mercury buoyancy (MB), and measurements o
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