On the competition in phase formation during the crystallisation of Al-Ni-Y metallic glasses

High-resolution, in situ synchrotron powder diffraction has been used to quantitatively follow the evolution of phases in 5 different alloys between Al87Ni9Y4 and Al75Ni15Y10, as they were continuously heated to melting and subsequently cooled back to ambient temperature. Upon heating, the first crystallisation product was found to vary from FCC Al to the intermetallic Al9Ni2 phase with increasing Ni concentration. In addition, the crystallisation sequence also changed from a two-stage to a three-stage process. High number densities of crystallites (∼1023 m−3) were observed initially for both FCC Al and Al9Ni2. The difference in competition in phase formation during heating and cooling are discussed in terms of nucleation barriers calculated using a recent thermodynamic assessment of the Al-Ni-Y system. The role of compositional heterogeneities in the as-quenched glasses and long range diffusion on the nucleation process is discussed.301