Measurement of dendrite growth velocity as a function of undercooling on Al68.5Ni31.5 alloy in reduced gravity

Abstract

Dendrite growth velocities are measured as a function of undercooling on Al–Ni alloys utilizing electromagnetic levitation. Various compositions were investigated. Whereas on the Ni-rich side, growth velocity increases with increasing undercooling, Al-rich alloys show an unusual decrease in growth velocity with increasing undercooling. Experiments on Al68.5Ni31.5 in reduced gravity (sounding rocket TEXUS 44) suggest that this anomalous behavior is caused by forced convection and is absent in µg. During the recent TEXUS 49 mission additional measurements of the dendrite growth velocity on the same alloy were performed and evaluated. In addition detailed post-mortem microstructure analyses have been performed to try to understand the growth mechanism of the Raney Al68.5Ni31.5 alloy. So far the unusual behavior of the dendrite growth velocity in undercooled melts of Al-rich Al-Ni alloys is not understood. Nevertheless the microgravity experiments helped to construct a hypothesis to explain the solidification mechanism of Al68.5Ni31.5