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.