Structural inhomogeneity and strain rate dependent indentation size effect in Zr-based metallic glass

The indentation size effect (ISE) of Zr-based metallic glass (MG) thin films at both as-deposited and annealed states was investigated. Nanoindentation tests performed at various penetration depths and applied strain rates demonstrated inverse ISE at shallow indentation depth and normal ISE at deep indentation depth, for both as-deposited and annealed MGs. Moreover, it was found that the normal ISE was strongly strain rate dependent and the structure-relaxed MG exhibited more pronounced ISE than that of the as-deposited one. Microstructural inhomogeneity caused by difference of areas between the preexisted liquid like flow units and the created free volume upon deformation was proposed to be a key parameter in dominating the pronounced ISE in structure-relaxed MG and the strong strain rate dependence of ISE.