Multi-scale inhomogeneity and anomalous mechanical response of nanoscale metallic glass pillar by cryogenic thermal cycling

The mechanical responses and structure variations of Ta₈₀Co₂₀ nanoscale metallic glass (MG) film samples upon cryogenic thermal cycling (CTC) treatment were studied. The simultaneous improvements of strength and deformation ability bring about a super-high strength of 4.5 GPa and a large plastic strain of about 80% after CTC treatment. The significant increase in inter-element bonding and hardness makes the activation and percolation of shear transformation zones to be more difficult and delays the yielding event, leading to the ultra-high strength. Although the TaCo MG pillar reaches a relaxation energy state, the micro- and nanoscale inhomogeneities remain induced by the local densely packed units along with crystal-like ordering embedded in the matrix. The multi-scale inhomogeneity can effectively hinder the sliding of the shear bands and improve their propagation stability, which is considered to be the origin of its excellent plasticity. Our study reveals another prospect of CTC treatment on nanoscale MG samples of constructing an anomalous inhomogeneous structure and obtaining simultaneous enhancement of strength and plasticity.