GRAIN REFINEMENT IN BULK UNDERCOOLED Ni-BASED ALLOY
(Northwestern Polytechnical University; Xi’an 710072; China)
Abstract: Fluxing of 5 g bulk melt Ni77Si13B10 permits high undercoolings to be attained prior to nu- cleation onset.Investigations of grain refinement in the bulk undercooled alloy as a function of undercooling,recalescence behavior and cooling rate have been reported.A significant inhomo- geneity of reduction in grain size of a bulk sample is observed,which is caused by the different so- lidification conditions:(1)recalescence process,and(2)the followed plateau in which the heat release and extraction rates are equal.It is concluded that the homogeneous refined microstructure can be achieved if the initial undercooling prior to nucleation,or cooling rate after recalescence is further increased.
Key words: Ni-based alloy; high undercooling; recalescence; grain refinement