1993 Volume 34 Issue 1 Pages 62-68
This study was aimed to improve the wettability of a non-wetting Al2O3 fiber/molten aluminum system, so as to attain full infiltration with a low applied pressure (Pa). The threshold infiltration pressure (Pc) of this composite system with an average fiber volume fraction (Vf) of 0.17 is 139 kPa at a molten aluminum temperature of 1023 K in pressure infiltration. Then non-infiltrated defects appear at locally high Vf portions. The θ of 2.24 rad is obtained taking into consideration the effect of non-infiltrated defects. Ultrasonic infiltration, in which ultrasonic vibration was transmitted into molten aluminum through a direct contact of the step-horn and melt, was performed to compare the apparent wettability with that in pressure infiltration. When molten aluminum was subjected to ultrasonic vibration with an ultrasonic power of 500 kW/m2 (resonant frequency of 20.5 kHz), the Pc becomes zero, that is, the melt entry occurs even with a zero Pa. An infiltrated area with a semi-spherical shape is observed on the cross section close to the step-horn at the initial stage of ultrasonic infiltration, which coincides with the ultrasonic pressure (Pus) distribution obtained analytically. Then non-infiltrated defects are not observed in an incorporated region. Ultrasonic infiltration seems to have a kind of driving force giving aid to realize full infiltration, such as improvement of the apparent wettability due to a hysteresis of contact angles, the Pus acted instead of Pa and the high vibrational acceleration.