Dissolution and precipitation under gravitational conditions in the W-Al system

Dissolution and precipitation in the system Al-W was investigated under different gravitational conditions and applied electric fields. An intermetallic phase, WAl4, precipitates after the dissolution of W into liquid Al. Settling of WAl4 precipitates was absent under all gravity and electric current conditions and a homogenous distribution of WAl4 with random alignment was observed in all cases. The size of the precipitates was found to increase with gravity. The electric current had a very small effect on the precipitate size in terrestrial gravity. However, under reduced gravity, the application of current resulted in a marked increase in precipitate size. Increasing gravity was found to increase the dissolution rate of W, which was discussed in terms of the stirring effect, created by the settling of W grains. Similar enhancement in the dissolution rate was observed with increasing electric current.