Wettability between Composing Materials and Metal for Composite Making.

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Wettability between composing materials and base metal matrix is an important factor for the strength of composite. Previously the wettability has been mainly determined from the contact angle in the sessile drop method. However, it is difficult to measure the exact value of , because of the presence of oxide film on the sessile drop surface of aluminium to have great affinity against oxygen. In present work, instead of the sessile drop method, the wettability between SiC or graphite and liquid aluminium or aluminium alloy was investigated by the dip coverage method where SiC or graphite disc ( 10 mm 5 mm) was dipped into molten metal and the ratio of the area wetted by metal on the SiC or graphite surface was determined. It was found that the wetting process between SiC or grahpite and molten metal had initially an incubation period that decreased by alloying IVa, Va and VIa elements in the dipping process of SiC and by IVa and Va elements in the case of grephite. The wetting process could be explained in the view-point of the nucleation rate for wetting. It was clear that the overall rate constant <k_o> obtained increased with addition of IVa, Va and VIa elements for SiC and IVa and Va elements for graphite, resulting in improvement of wettability. The activation energy for wetting process between SiC and Al, Al-Ti, Al-V and Al-Zr was obtained such as in the range from 327 to 335 kJ/mol and , for graphite system, was obtained as from 365 to 390 kJ/mol. Those values are approximately agreed with the single bonding energy of Si-C or C-C, suggesting that the wetting process is limitted by the dissociation process of SiC or graphite. The values of <k_o> and incubation period indicate a periodic relation to the atomic number of the element, which is similar to the behavior of the interaction parameter for carbon activity coefficient in liquid iron. Consequently, the wettability may be improved by increase of carbon solubility in liquid aluminium by alloying.