Thermal activation in Au-based bulk metallic glass characterized by high-temperature nanoindentation
High-temperature nanoindentation experiments have been conducted on a Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass from 30 to 140 C, utilizing loading rates ranging from 0.1 to 100 mN/s. Generally, the hardness decreased with increasing temperature. An inhomogeneous-to-homogeneous flow transition was clearly observed when the test temperature approaches the glass transition temperature. Analyses of the pop-in pattern and hardness variation showed that the inhomogeneous-to-homogeneous transition temperature was loading-rate dependent. Using a free-volume model, we successfully deduced the size of the basic flow units and the activation energy for the homogeneous flow. In addition, the strain-rate dependency of the transition temperature was predicted.