Synthesis of metallic glass composites using phase separation phenomena

Phase separation phenomena in metallic glass systems have been explored by thermodynamic calculation and experimental method in the present study. Miscibility gap and spinodal curve for liquid phase in Gd-Ti-Al-Co/Cu systems have been calculated using the CALPHAD method. Based on the calculation result, various types of phase separation phenomena have been observed experimentally. Basically two types of structure are observed: interconnected-type structure by spinodal decomposition; and droplet-type structure by nucleation and growth mechanism. Multi-step phase separation occurs during cooling from the liquid, forming a hierarchical length scale composite structure. Depending on the glass-forming ability of the separated liquid phase, amorphous/amorphous or amorphous/crystalline composite structure can be obtained. The present study shows that there are several factors such as critical temperature, asymmetry and composition range of the spinodal curve which affect scale and morphology of the microstructure after phase separation. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.