Boron Heterogeneities in As-Cast FeAl Intermetallics

Abstract
Boron analysis of B doped FeAl alloys, in the as-cast condition, can give surprising results : large enrichments of B at the surface of ingots are systematically observed. The variations of B in a section of a 30 mm diameter ingot (Fe-25wt%Al-150ppmB) are typically : 180ppm B at the surface and 140 ppm B in the centre of the ingot. However, when single crystals are grown at low cooling rates (solid/liquid interface velocity about 3mm/h), the segregation of boron is regular : enrichment in the final part of the crystal is found. In Fe-B alloys, no boron segregation was found. Boron enrichment at the surface of as-cast FeAl ingots might be due to segregation of B in the liquid state by interaction with alumina superficial layers.