Thermodynamic and kinetic modelling of primary crystallisation in amorphous alloys

The aim of this paper is to apply thermodynamic and kinetic modelling to primary crystallisation in metallic glasses. The CALPHAD method has been used to obtain an assessment of stable and metastable phase diagrams. Amorphous phases have been described as undercooled liquids. The moving boundary model has been applied to simulate the growth of nuclei into the amorphous matrix. A thermodynamic assessment of stable and metastable phase diagrams is reported for Fe-B and Al-Ni-Ce systems. From calculated thermodynamic functions, driving forces for nucleation have been estimated as a function of temperature and composition. The growth of bee Fe into a Fe85B15 amorphous alloy has been simulated at 650 K. A composition gradient at the crystal/amorphous interface is obtained at the beginning of the treatment, which progressively overlaps with that of the next crystal. It has been shown that the crystal growth enriches in B the residual amorphous matrix, hindering further nucleation. The growth at 553 K of an fcc-Al nanocrystal into an Al87Ni10Ce3 amorphous alloy has been simulated and the effect of the diffusion coefficients of the various elements on composition profiles has been evidenced.