Deformation behavior and indentation size effect of Au₄₉Ag_5.5Pd_2.3Cu_26.9Si_16.3bulk metallic glass at elevated temperatures

Instrumented nanoindentation was conducted on an Au49Ag5.5Pd2.3Cu26.9Si16.3bulk metallic glass from room temperature to supercooled liquid region. It was found that the hardness decreases as the depth of the indentation increases at a modest loading rate (e.g. ∼0.5 mN s-1), which is known as the indentation size effect (ISE). The transition from inhomogeneous to homogeneous flow was clearly observed at the glass transition temperature. However, the deformation behavior of the metallic glass in the supercooled liquid region showed strong loading rate dependence. The deformation mode changed from homogeneous to inhomogeneous, and even exhibited a reverse indentation size effect when the loading rate was sufficiently high (i.e., ≥10 mN s-1in the study). The different deformation behaviors and indentation size effects at various temperatures and loading rates are discussed in terms of free volume theory.