Microstructure characteristics of high undercooled bulk nanocrystalline Fe-B-Si eutectic alloy

By applying cyclical superheating incorporated with glass fluxing denucleation method, the maximum undercooling of 367 K was obtained for 6 - 20 g Fe76B12Si12 eutectic bulk liquid alloy. Using high undercooling and quenching the high undercooled alloy into water, nanocrystalline bulk Fe76B12Si12 eutectic alloy with 11 mm in diameter, 10 mm in height and average particles size of about 200 nm has been prepared. It has been found that the microstructures vary with preparing conditions. For the sample triggered at 367 K undercooling after recalescence by the cooling rate of 4 K/s cooling to room temperature and for the sample triggered at 329 K undercooling after recalescence and quenching, the microstructure consists of 30 - 400 nm α-Fe(Si) particles distributed uniformly in the refined Fe2B(Si) matrix, whereas for the sample triggered at 354 K undercooling in the process of recalescence and quenching, the microstructure consists of 30 - 350 nm Fe2B(Si) particles distributed uniformly in the α-Fe(Si) matrix. The radial microstructure difference can be improved by increasing the initial undercooling and cooling rate. The reasons of microstructure refined to nanometer level were discussed.