Glass formation versus nanocrystallization in An Al92Sm8 alloy

Solid state glass formation is often viewed as a non-equilibrium process resulting from the destabilization of crystalline phases when the maximum metastable solubility is exceeded. This simple model is depicted by a generalized phase diagram for partitionless transformations (1). Within this perspective, glass formation is enabled by rapidly quenching a homogeneous melt or, alternatively, by compositional variation at constant low temperature leading to equivalent glassy states. This prediction has been confirmed experimentally for several easy glass-forming alloys (2,3). Yet, it has been found previously that a significant number of melt quenched amorphous alloys often do not show a distinct glass transition as the initial thermal signal on heating, but instead an exothermic maximum, indicating a partial nanocrystallization reaction (4-6). These amorphous alloys have been classified as marginal glass formers since the amorphization is related mainly to growth kinetics limitations rather than nucleation difficulties (7). In this work, glassy Al92Sm8 alloys which have been obtained by both rapid quenching and deformation mixing techniques have been studied as a representative of a marginal glass forming material. The samples were examined to explore whether the nucleation of nanocrystals can be avoided by choosing an appropriate reaction pathway and whether the changes in the reaction pathway can influence the kinetic stability of the amorphous phase.