Crystallisation behaviour of rapidly quenched cast irons with small amount of boron

Amorphous cast irons (with carbon content varying from 12.01 to 15.01 at.%) containing 1 and 2 wt.% of boron, were produced by rapid quenching from the melt in the form of ribbons with thickness of 40–75 μm. The crystallisation process of the amorphous alloys was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM).Very strong influence of boron content on thermal stability and crystallisation process of the alloys studied was observed. The increase of boron content from 1 to 2 wt.% resulted in the increase of crystallisation onset temperature by about 100 K and in the change of crystallisation mode. The number of crystallisation stages, observed during calorimetric studies at temperatures reaching 1000 K, drops from three to one when boron content increases from 1 to 2 wt.%. This indicates a change from primary to eutectic mode of decomposition of the amorphous phase, although in both cases similar crystallisation products are formed: α-Fe(Si) and Fe3(C,B). In primary crystallisation mode, dendritic crystals of α-Fe(Si) are formed and in eutectic crystallisation of both phases, small elongated crystallites are observed.