**5. Conclusions**

Our results show a clear e ffect of hydrogen on the mechanical behavior of a Vit 105 MG. With increasing hydrogen content up to 0.29 H/M, the load of the first pop-in increases, consistent with the observed increase in hardness and modulus, while the occurrence of pop-ins decreases. This results in a transition from pop-in or shear banding to homogeneous deformation at a hydrogen content of 0.29 H/M. The behavior is interpreted in terms of hydrogen stabilization of STZs in the amorphous structure due to the negative enthalpy of mixing of hydrogen with Zr. Thus, charging of MGs with negative heats of mixing with low concentration of hydrogen may o ffer a robust method to increase modulus and hardness and prevent catastrophic shear band formation in MGs.

**Author Contributions:** Conceptualization, L.T., D.T. and C.A.V.; Methodology and Formal Analysis, D.T., M.H. and T.S.; Writing—Review and Editing, L.T., D.T. and C.A.V.; Funding Acquisition, L.T., Z.S. and C.A.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** L.T. acknowledges the Natural Science Foundation of China (Grant 51501144), the China Postdoctoral Science Foundation (2015M580842), and the Alexander von Humboldt Foundation for financial support. C.A.V. and D.T. acknowledge financial support by the German Research Foundation (DFG) through an individual gran<sup>t</sup> (VO 928/9-1). Z.W.S. acknowledges support by the National Key Research and Development Program of China (No. 2017YFB0702001) and Natural Science Foundation of China (51231005 and 51621063).

**Acknowledgments:** We would also like to thank Feng Jiang and Mingcan Li for providing the samples.

**Conflicts of Interest:** The authors declare no conflict of interest.
