Stimulation of shear-transformation zones in metallic glasses by cryogenic thermal cycling

Cryogenic thermal cycling (CTC, between room temperature and 77 K) of a (Cu,Zr)-based bulk metallic glass (MG) leads to substantial reductions in the initial yield load F-y observed on instrumented indentation, and can reverse annealing-induced increases in Fy. In contrast, for hardness and elastic modulus, CTC has much less effect and can only partially reverse annealing effects. The distribution of Fy values is wide, reflecting heterogeneity in the MG. For a melt-spun Fe-based glass, CTC with more cycles induces similar changes in F-y, and has almost no effect on the magnetic properties. Such differing effects of CTC can be consistently interpreted in terms of its preferential effect on soft spots in a relatively rigid glass matrix. The capability for targeted stimulation of shear-transformation zones permits tailoring of MG properties, clearly facilitates initiation of plastic flow, and offers the prospect of improved plasticity and toughness even in annealed samples.