Gravity effects on reactive settling in the Al-W system in SHS

Reactive settling in the system Al-W was investigated under different gravitational conditions and applied electric field. Samples of 0.1W + 1.0Al were reacted under conditions of 0, 0.16 (lunar gravity), 1.0, and 1.8 g. Non-terrestrial gravity experiments were carried out onboard NASA KC-135 aircraft. The reactive settling involved a process of dissolution of W into liquid Al, the formation of WAl4, and the settling of the partially reacted W particles. Settling of W was absent under 0 g, partial settling was observed under 0.16 g, and complete settling was observed under 1.0 and 1.8 g conditions. The effect of temperature on settling and microstructural evolution was investigated. The results are interpreted in terms of competing processes of settling, reactivity, and nucleation of the aluminide.