compared to the initial primary spacing (fig. 5, right, : Studie 
lower end between x=10 and x=11mm), after the on the 
melting/resolidification process a significantly larger J 
primary spacing is found. De 
In the equiaxed samples, the concentration profiles are Ll 
similar to those in the directionally solidified samples " 
(fig. 4). However, in addition to the concentration gra- | 
dient a gradient of the grain size and grain aspect ratio ons 
develops. As the solidification front moves toward 
regions with higher temperatures, the grains get more ; 
and more elongated. In addition to the elongation of the ee 
grains and similarly as for the columnar microstructure, Metasial 
the length scale of the microstructure is changing . elevated 
during the melting/resolidifiation process. As compared Suen 
to the initial grain size of the equiaxed grains (fig. 5, ie 
left, lower end, between x=10 and x=11mm), a signi- 5 
ficantly larger grain size is observed. 
where 
x fm 
dw =0- 
Conclusions u 
The experimental set-up with the steep temperature 
gradient provides an excellent tool for studying the Eperim 
kinetics of melting. The substantial change of length Wels 
scale and the grain elongation in the equiaxed sample (TEL 
show that the mushy zone undergoes a complex phase ; 
transformation process. Further work is needed to me 
separate and identify the different processes leading to 
the observed microstructures. 9 
References 9 I 
I. E.E. Emley, Int. Metall. Rev 21 (1976) 75-115 
2. M.C. Schneider, J.P. Gu, C. Beckermann, W.J. 
Boettinger, U.R. Kattner, Metall. Mater. Trans 28A Fig. 5: Microstructures after 1h for 4 
(1997) 1517-1531 initially equiaxed (left) and 
columnar (right) samples 
316