Fe-30at.%Co alloy is undereooled to investigate the effct of remelting on the grain size at certain undereooling rnnges. At low undereoolings, the primary stable fcc phase is remelted, which results in the equiaxed gr...Fe-30at.%Co alloy is undereooled to investigate the effct of remelting on the grain size at certain undereooling rnnges. At low undereoolings, the primary stable fcc phase is remelted, which results in the equiaxed grains. When the melt is undercooled greater than the critical undereooling △T=204K the primary metastable bcc phase will alternatively nucleate in the melt. The primary bcc dendrite will be remelted into isolated dendrite cores dispersing in the remaining liquids. In the meanwhile, the isolated dendrite cores are remelted more or less due to the temperature fluctuation in the liquids. Different crystal structures between bcc and fcc phase make the subsequent crystal growth of fcc phase onto the Primary bcc phase non-epitaxial when the melt is undereooled greater than △T=204K. The primary metastable bcc phase may play an important role in coarsening grains in the systetn at larpe undereoolings.展开更多
Undereooling eoperiments on binary Ni50 Cu50 alloy melts were conducted. The hypercooling limit of this alloy, which is about 310K, was evaluated by mcasuring plateau time needed for the interkendritic liquid solidifi...Undereooling eoperiments on binary Ni50 Cu50 alloy melts were conducted. The hypercooling limit of this alloy, which is about 310K, was evaluated by mcasuring plateau time needed for the interkendritic liquid solidification and extmpolating this function to zero. This limit was exceeded first in the binary alloy undereooled by about 320K.The effect of liquid undercooling on the respective microstructure evolution was studied by optical metallogrnphy. The hypercooled microstructure contains rcsidual fragments within grain boundaries and is quite different from those obtained at undercoolings below 310K. The finding indicated the existence of dendrite break up. The dendrite break up may be induced either by remelting or by stress. By considering hyperrooling conditions and comparing two grain ndnement microstructures observed at small and larpe undereoolings, the forms of dendrite break up and the grain refinement mechanism exceeding the hypereooling limit are further discussed.展开更多
文摘Fe-30at.%Co alloy is undereooled to investigate the effct of remelting on the grain size at certain undereooling rnnges. At low undereoolings, the primary stable fcc phase is remelted, which results in the equiaxed grains. When the melt is undercooled greater than the critical undereooling △T=204K the primary metastable bcc phase will alternatively nucleate in the melt. The primary bcc dendrite will be remelted into isolated dendrite cores dispersing in the remaining liquids. In the meanwhile, the isolated dendrite cores are remelted more or less due to the temperature fluctuation in the liquids. Different crystal structures between bcc and fcc phase make the subsequent crystal growth of fcc phase onto the Primary bcc phase non-epitaxial when the melt is undereooled greater than △T=204K. The primary metastable bcc phase may play an important role in coarsening grains in the systetn at larpe undereoolings.
文摘Undereooling eoperiments on binary Ni50 Cu50 alloy melts were conducted. The hypercooling limit of this alloy, which is about 310K, was evaluated by mcasuring plateau time needed for the interkendritic liquid solidification and extmpolating this function to zero. This limit was exceeded first in the binary alloy undereooled by about 320K.The effect of liquid undercooling on the respective microstructure evolution was studied by optical metallogrnphy. The hypercooled microstructure contains rcsidual fragments within grain boundaries and is quite different from those obtained at undercoolings below 310K. The finding indicated the existence of dendrite break up. The dendrite break up may be induced either by remelting or by stress. By considering hyperrooling conditions and comparing two grain ndnement microstructures observed at small and larpe undereoolings, the forms of dendrite break up and the grain refinement mechanism exceeding the hypereooling limit are further discussed.
