Containerless Solidification and Characterization of Industrial Alloys (NEQUISOL)

Kurzfassung

Containerless solidification using electromagnetic levitator, gas atomization and an instrumented drop tube, known as impulse atomization is investigated. Effect of primary phase undercooling on dendrite growth velocity of Al-Ni alloys under terrestrial and reduced-gravity condition is discussed. It is shown that with increasing undercooling in the Ni-rich alloys the growth velocity increases, whereas in the Al-rich alloys the growth velocity decreases. However, the Al-rich alloy in microgravity shows similar behavior to that of Ni-rich alloys. Furthermore, the effect of cooling rate on the phase fractions, metastable phase formation and Al3Ni2 lattice parameter of impulse-atomized Al-Ni alloys is discussed. In addition, the effects of primary phase and eutectic undercooling on the microstructure of Al-Fe alloys are investigated. The TEM characterization on the eutectic microstructure of impulse-atomized Al-Fe powders with two compositions shows that the metastable AlmFe forms in these alloys. Also, the growth undercooling that the dendritic front experiences in the solidification of the droplet results in variation of dendrite growth direction from <100> to <111>. For Al-4 at%Fe, it is found that in the sample solidified in reduced-gravity and in the impulse-atomized droplets the primary intermetallic forms with a flower-like morphology, whereas in the terrestrial EML sample it has a needle like morphology. A microsegregation model for the solidification of Al-Ni alloys is presented that accounts for the occurrence of several phase transformations, including one or several peritectic reactions and one eutectic reaction.