Enhanced strain rate sensitivity in thermal-cycling-rejuvenated metallic glasses

Highlights: • Enhanced strain rate sensitivity m was derived in MG after thermal cycling. • Both positive and negative flow units play roles in the rate-sensitive strength. • Competition in time spans of structural evolution and strain rate dominates the m. • Strain rate sensitivity of MG can be altered by tailoring the size of flow units. -- Abstract: Strain rate sensitivity (SRS) is an effective parameter to demonstrate the deformation mechanism of metallic materials. However, despite extensive research, the meanings of the SRS of metallic glasses (MGs) were still vague and controversial results largely remained. In the present study, with altering the microstructural features of the magnetron sputtering CuZr MG before and after thermal cycling treatment, the effects of size of both positive and negative flow units on SRS were evaluated by amplitude-modulation atomic force microscopy (AM-AFM) and nanoindentation testing. Positive SRS index m was derived in the CuZr MG, and m increased from 0.014 to 0.040 after thermal cycling. The mechanism of the enhanced SRS and underlying microstructural evolution were explored and proposed. It shows the competition between time scales of atom rearrangement within flow units and applied loading strain rate causes the change of SRS, and both the size of positive and negative flow units play crucial roles in determining the magnitude of SRS.