Rapid monotectic solidification under free fall condition

摘要

Fe-48.8 percent Sn monotectic, Fe-40 percent Sn hypomonotectic and Fe-58 percent Sn hypermonotectic alloys have been rapidly solidified during free fall processing in drop tube. For droplets of 100-1000 mu m, the maximum undercooling for Fe-48.8 percent Sn, Fe-40 percent Sn and Fe-58 percent Sn alloys is 270, 282 and 288 K respectively. For Fe-48.8 percent 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 mu m and undercooling is 30 K. For Fe-40 percent Sn hypomonotectic alloy, the microstructure undergoes a transition from columnar alpha-Fe dendrites distributed in Sn-rich matrix to alpha-Fe particles. The growth velocity of alpha-Fe dendrite changes from 0.45 to 4.65 m/s when the droplet diameter varies from 1000 to 100 mu m. For Fe-58.8 percent Sn hypermonotectic alloy, the grain size of primary a-Fe dendrites decreases remarkably when undercooling increases.