Deformation processes in metallic glasses are known to be inhomogeneous in space and jerky in time, but there is a lack of in situ, nondestructive evaluation of such processes on appropriate spatiotemporal scales. First, we have utilized a nanomechanical testing method to measure the stresses for the onset of plasticity, and developed a stochastic statistical model to characterize the structural heterogeneity. It is found that, with increasing the structural relaxation, the defect density drops significantly and the fracture of metallic glasses changes from a metal-like mode to that of fragile glass. Second, an unmixing method from signal processing is employed to identify the localized heat sources inside the bulk from the measured thermographs on the surface. From a linear instability analysis, the evolution of this heterogeneous process proves the coupled structural/thermal softening mechanisms.
Acknowledgements: Research supported by the US Department of Energy, BES, Materials Sciences and Engineering Division.