Microstructural characterization of arc-melted and directionally solidified near-eutectic molybdenum–silicon–boron alloys

Samples of near-eutectic Mo–Si–B alloys, with the nominal composition corresponding to the Moss + Mo3Si + T2 eutectic area, were prepared by arc-melting or by crucible-free zone-melting methods (directional solidification). In the directionally solidified (DSed) alloy, the volume fraction of the Moss + Mo3Si + T2 eutectic cells appeared to increase compared with that of arc-melted (AMed) alloy, and well-aligned and rod-shaped Moss and T2 phases were formed in a Mo3Si matrix of the eutectic cells. In the AMed alloy, only the T2 phase showed a <100] preferential growth orientation along the solidification direction, whereas the Moss phase displayed no obvious preferred orientation. The Mo3Si matrix showed a weak preference toward <001> growth along the solidification direction in the AMed alloy, and this became much stronger in the DSed alloy. Furthermore, the DSed alloy exhibited an apparent preferential growth orientation relationship of <001>Moss//<001>Mo3Si//<100]T2 along the solidification direction. However, no specific atomic structures were observed at the interfaces, indicating that the three phases grew independently from the liquid without the formation of any habit interface during solidification.