The Influence of Cooling Rate and Alloy Composition on the Formation of Borides during Solidification of Boron-containing TiAl Alloys

摘要

Transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) have been used to identify the crystal structures of long curvy and blocky borides which are formed at different cooling rates in TiAl-based alloys. It has been found that for Ti-45Al-2Nb-2Mn-lB the long curvy borides were either TiB borides with B1 structure or Ti3B4 borides,and the blocky borides were either TiB borides with B27 structure or TiB2 borides. However.for Ti-48Al-2Cr-2Nb-lB both long curvy borides and blocky borides were found to be TiB2 orides. It is inferred that the crystal structures of borides are both composition and cooling rate related.