“Big cube” phase formation in Zr-based metallic glasses

The formation of a metastable fcc NiTi2-type intermetallic compound (big cube phase) from Zr-based metallic glasses have been studied in this work. This phase was found in partially crystalline Zr52.5Cu17.9Ni14.6Al10Ti5 amorphous ribbons. Its nucleation could be avoided by adding 2% of Y, which acts as an oxygen scavenger. After annealing a fully amorphous ribbon, nanocrystals of the big cube phase have been observed. The Zr55Cu30Ni5Al10 alloy has been partially amorphised by copper moulding and arc melting. Large agglomerates of crystals of the big cube phase have been found embedded in the amorphous matrix. Also for this alloy, nanocrystal of the same phase has been found after crystallisation. From the results, it appears clear that the big cube phase nucleates first from the undercooled liquid. Its formation is hindered if the oxygen content in the undercooled liquid alloy is significantly reduced. After solidification, coarse grains were found, whereas nanocrystals were produced by crystallisation. The role of nucleation on the crystallisation process is briefly discussed.