Unraveling the origin of stress-dependent glass transition temperature in metallic glasses

Abstract

The effect of externally applied stress on glass transition temperature Tg, whose underlying mechanism remains a fascinating and open question in materials science and condense-matter physics, has been explored in a range of metallic glasses (MGs) in the last decades. Recent studies have found that hydrostatic pressure leads to a slight increase in Tg, while uniaxial compression causes notable decrement. However, the origin of stress-dependent Tg variation is largely unknown. Here we report new results of tensile stress effect on Tg in a Ni60Nb40 (at.%) MG through in situ tensile loading and high temperature synchrotron radiation X-ray diffraction measurements. Combining our experimental data with available reports on hydrostatic pressure and uniaxial compression, a universal picture of stress-induced variation in Tg of MGs under various stress states was obtained. We elucidate the physics underlying the stress-induced Tg variation by decomposing the uniaxial tensile stress into a hydrostatic stress combined with two pure shear stresses, and investigating the individual contributions of the decomposed stress states on Tg by atomistic simulations. Our results reveal an enhanced stress effect on Tg through a combination of different stress components. The variation in Tg was linked with stress-aided changes in local atomic configurations. Our theoretical predictions are shown to be in remarkable agreement with experiments, and fill the gap in the current understanding of stress-dependent Tg in MGs.