Crystallization behavior of thermally rejuvenated Zr50Cu40Al10 metallic glass

Abstract

The recovery annealing technique was used to clarify the crystallization behavior of a rejuvenated Zr50Cu40Al10 metallic glass. Specific heat and thermal expansion measurements showed that the glassy states of fast cooled and recovery annealed samples are almost identical from the energetic and volumetric points of view. Dynamic mechanical analysis also suggested that their internal microstructures resemble each other. These results indicate that the glassy state and the structure can be controlled according to the final cooling conditions from the supercooled liquid region. However, a clear difference of the incubation time for crystallization was observed between the fast cooled and recovery annealed samples, implying that thermal accumulation seems to mostly correlate to the crystallization rather than to atomic diffusion through the newly created excess free volume in the rejuvenated sample. In addition, a transmission electron microscopy image of the sample, performed on double sets of the recovery annealing process, shows a precipitation of the crystalline phase with approximately 50 nm in diameter in the amorphous matrix. These results suggest that the recovery annealing independently leads to two different thermal paths, one towards structural rejuvenation and the other towards crystallization. The high-resolution transmission electron microscopy result of the recovery annealed sample indicates that these two regions co-exist in the amorphous matrix.