Crystal-growth velocity in metallic melts has been reported by others to increase monotonically with undercooling. Nevertheless, such an observation is not predicted by conventional growth theory. In this work, the metallic melt of Zr 50 Cu 50 is studied to address the problem by measuring the growth velocity over a wide range of undercooling up to 325 K. A maximum growth velocity is observed at an undercooling of 200 K instead of the monotonic increase reported in the literature. We find that the planar or dendrite growth theories can explain the value of the maximum growth velocity, but the predicted location of the maximum in undercooling is far less than that seen by experiment. With the assistance of current results, a general pattern of crystal growth is established for melts of a variety of substances, where all sluggish crystal-growth kinetics is explained by the diffusion-controlled mechanism at deep undercooling.

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Structural evolution in nanoscale Cu50Zr50 metallic glasses during high-pressure torsion is investigated using molecular dynamics simulations. Results show that the strong cooperation of shear transformations can be realized by high-pressure torsion in nanoscale Cu50Zr50 metallic glasses at room temperature. It is further shown that high-pressure torsion could prompt atoms to possess lower five-fold symmetries and higher potential energies, making them more likely to participate in shear transformations. Meanwhile, a higher torsion period leads to a greater degree of forced cooperative flow. And the pronounced forced cooperative flow at room temperature under high-pressure torsion permits the study of the shear transformation, its activation and characteristics, and its relationship to the deformations behaviors. This research not only provides an important platform for probing the atomic-level understanding of the fundamental mechanisms of high-pressure torsion in metallic glasses, but also leads to higher stresses and homogeneous flow near lower temperatures which is impossible previously.

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