*Communication* **E**ff**ect of Hydrogen Charging on Pop-in BehaviorZr-BasedMetallicGlass**

**Lin Tian 1,2,\*, Dominik Tönnies 1, Moritz Hirsbrunner 1, Tim Sievert 1, Zhiwei Shan 2 and Cynthia A. Volkert 1,\***


Received: 12 November 2019; Accepted: 18 December 2019; Published: 22 December 2019

**Abstract:** In this work, structural and mechanical properties of hydrogen-charged metallic glass are studied to evaluate the e ffect of hydrogen on early plasticity. Hydrogen is introduced into samples of a Zr-based (Vit 105) metallic glass using electrochemical charging. Nanoindentation tests reveal a clear increase in modulus and hardness as well as in the load of the first pop-in with increasing hydrogen content. At the same time, the probability of a pop-in occurring decreases, indicating that hydrogen hinders the onset of plastic instabilities while allowing local homogeneous deformation. The hydrogen-induced sti ffening and hardening is rationalized by hydrogen stabilization of shear transformation zones (STZs) in the amorphous structure, while the improved ductility is attributed to the change in the spatial correlation of the STZs.

**Keywords:** metallic glass; hydrogen; indentation; pop-in; plasticity
