Phase separation in Cu₄₆Zr_47-xAl₇Gd _x metallic glasses

The influence of Gd addition on phase separation of rapidly quenched Cu₄₆Zr_47-xAl₇Gd_x metallic glasses (x = 2,5,7) was studied. For low Gd content (x = 2), a homogeneous glass is obtained for the as-quenched state. Annealing leads to cluster formation by nucleation and growth prior to crystallization. For the Gd contents x = 5 and 7, early stages of spinodal decomposition are observed in the as-quenched glasses. Further annealing increases the amplitude of the compositional fluctuations prior to crystallization. Atom probe tomography gives evidence of the presence of Gd-enriched clusters of 2-5 nm size for the Cu₄₆Zr ₄₂Al₇Gd₅ glass. The structure formation as a function of the Gd content is essentially determined by the composition dependence of the miscibility gap of the metastable undercooled melt. Early stages of spinodal decomposition or almost homogeneous glassy states are obtained if the critical temperature of liquid-liquid phase separation is close or below to the glass transition temperature.