Formation of crystallographically aligned BiMn grains by semi-solid processing of rapidly solidified Bi-Mn alloys under a magnetic field

Alignment of the BiMn grains during solidification under a magnetic field was examined for Bi-Mn alloys (20,30,40 and 50at%Mn). During the conventional peritectic solidification, the BiMn grains produced through the peritectic reaction did not align because of difficulties of the grain rotation. Rapid solidification produced the finely distributed BiMn grains in the Bi-rich matrix or the Bi-BiMn eutectic structure at off-eutectic compositions. Heating the rapidly solidified structure resulted in the semi-solid state even for Bi-50 at%Mn alloy, in which no semi-solid state containing BiMn phase in equilibrium. The BiMn grains suspended in the semi-solid state rotated in the favorable direction. Growth of the BiMn grains following the rotation achieved c-axes alignment of the BiMn grains. The semi-solid state, which is controlled by the initial microstructure obtained by the rapid solidification, is significantly useful for the magnetic alignment.