Rapid monotectic solidification under free fall condition

Fe-48.8% Sn monotectic, Fe-40% Sn hypomonotectic and Fe-58% Sn hypermonotectic alloys have been rapidly solidified during free fall processing in drop tube. For droplets of 100-1000 μm, the maximum undercooling for Fe-48.8% Sn, Fe-40% Sn and Fe-58% Sn alloys is 270, 282 and 288 K respectively. For Fe-48.8% Sn monotectic alloy, a homogeneously dispersed microstructure can be obtained when the droplet diameter is small, and the Marangoni migration velocity V_m is 37 times as fast as Stokes velocity V_s when the dispersion sphere radius is 6 μm and undercooling is 30 K. For Fe-40% Sn hypomonotectic alloy, the microstructure undergoes a transition from columnar α-Fe dendrites distributed in Sn-rich matrix to α-Fe particles. The growth velocity of α-Fe dendrite changes from 0.45 to 4.65 m/s when the droplet diameter varies from 1000 to 100 μm. For Fe-58.8% Sn hypermonotectic alloy, the grain size of primary α-Fe dendrites decreases remarkably when undercooling increases. Copyright by Science in China Press 2004.