Wetting of ceramic particulates with liquid aluminum alloys: Part II. Study of wettability |
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Authors: | S Y Oh J A Cornie K C Russell |
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Affiliation: | (1) Massachusetts Institute of Technology, 02139 Cambridge, MA |
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Abstract: | Wetting phenomena in ceramic particulate/liquid Al-alloy systems were investigated experimentally using a new pressure infiltration
technique developed by the authors. Studies were performed on two different ceramic particulates, SiC and B4C, with four different liquid aluminum alloy matrices, pure Al, Al-Cu, Al-Si, and Al-Mg. Five major variables tested to study
wetting phenomena in ceramic/Al-alloy systems were holding time, melt temperature, alloying element, gas atmosphere, and particulate.
Metal: ceramic interfaces were investigated with optical microscopy, SEM, EPMA, and Auger Electron Spectroscopy (AES) in order
to understand better the wetting process. The threshold infiltration pressure decreased with, temperature as well as with
pressurization time for all the ceramic/metal systems. A strong correlation was found between the alloying effect on the threshold
pressure and the free energy of formation of oxide phase of the alloying element. More reactive alloying elements were more
effective in improving wettability. In air atmospheres, the threshold pressure usually increased markedly as a result of a
thick oxide layer formation on the liquid front. Compacts of B4C particulates showed lower threshold pressures than those of SiC, particulates. Fracture occurred in a generally brittle
manner in infiltrated SiC, specimens. AES element profiles on the fracture surfaces showed fast diffusion of Si, and pile-up
of C at the metal∶SiC boundaries which promoted fracture through the carbon-rich layer. The fracture surfaces of infiltrated
B4C specimens indicated plastic deformation, hence a more ductile failure mode. |
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