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The microstructure of Nb SS -Nb 5 Si 3 eutectic alloys unidirectionally solidified at various growth rates and the phase boundary characteristics between niobium solid solution (Nb SS ) and Nb 5 Si 3 phases in these alloys were studied, by using electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD) method. Lower growth rate is beneficial to form lamellar eutectic structure. When the growth rate decreased to 3 mm/h, large-scale regular lamellas could be detected in alternative distribution. Three kinds of crystallographic orientation patterns, i.e. {111}Nb//{011}Nb 5 Si 3 , {110}Nb//{111}Nb 5 Si 3 and {112}Nb//{100}Nb 5 Si 3 were identified in lamellar and non-lamellar eutectic structures with different growth rate conditions. Associated with the X-ray diffraction (XRD) results about investigated alloys, two-phase eutectic growth shows strong preferential orientation when growth rate is low. The influence of growth rate on microstructural evolution in unidirectionally solidified Nb SS -Nb 5 Si 3 eutectic alloy had been discussed in this paper.

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