The stochastic transition from size dependent to size independent yield strength in metallic glasses

It has been an enduring and heated debate whether the yield strength of metallic glasses (MGs) is size dependent or size independent. In this work, we first develop a micromechanical model by taking into account the stochasticity for shear band initiation in microcompression. Our modeling is subsequently verified through the extensive in-situ and ex-situ microcompression experiments. Through the efforts of combined experiments and modeling, we show a size-controlled stochastic transition from the size dependent to the size independent yield strength in the MG micropillars. Such a stochastic transition is featured with a strong fluctuation in the measured yield strengths when the micropillar size is near an intrinsic length scale which varies with the chemical composition of MGs. In contrast, such a size-controlled transition appear deterministic with little data scattering in tension. At the fundamental level, our results unfold a size dependent shear band initiation process in MGs, which may be applicable to other amorphous materials of technological importance.