In situ electrochemical experiments were carried out during quasi-static three-point bending of bulk glassy Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 5 alloy (Vit105) samples in air and in 0.01 M Na 2 SO 4 solution. Shear banding creating shear steps at surface break locally the naturally formed passive film resulting in a clear open circuit potential drop. Under potentiostatic polarization conditions, formation of shear steps causes narrow peaks in current density. By both methods, early shear banding can be detected before it can be inferred from macroscopic strain measurements.Most bulk metallic glasses (BMGs) show high strength values in combination with a large elastic deformation, which makes them very attractive for various applications. Concerning the quasi-static deformation behavior of fully amorphous bulk metallic glasses many investigations have been conducted and the versatile results are widely reported in literature. [1][2][3][4] But their lack of plasticity under mechanical loading, especially at tensile stresses, still poses an important drawback to their breakthrough as widely used structural materials. Particularly, the early stages of damaging are of great interest in this context. For this account, we developed a new technique taking advantage of discrete surface changes caused by shear banding, which are detectable by in situ electrochemical measurements. The prominent Zr-based BMG Vit105 was chosen as testing material in the current work, since it was identified as reliable target for complex mechanical analysis. [5] Versatile electrochemical investigations concerning the relation between corrosion and shear banding have been conducted for Zr-based amorphous alloys so far. In this context, Gebert et al. investigated the influence of mechanically generated surface defects on the pitting corrosion behavior of a Zr-based BMG in halide containing solutions. Moreover, they conducted a series of compression tests on samples with preformed corrosion pits to investigate the relationship between pitting and shear banding. [6] Wang et al. proposed a model which describes that pitting corrosion preferentially takes place at shear offsets. [7] Vit105 was recently analyzed concerning chemical breakdown events of the passive film without mechanical loading [8] and under static loading [9] both in a halide containing electrolyte. Since in the present study the pure deformation behavior of Vit105 bending samples is investigated, an inert 0.01 M Na 2 SO 4 solution was chosen for in situ electrochemical analysis. By the exploitation of the very sensitive electrochemical response of the Zr-based BMG to changes of the surface state, which are caused during deflection by the generation of small shear steps breaking the passive film, it is possible to detect and analyze the earliest stages of shear banding in situ during mechanical loading.
ExperimentalThe Zr-based bulk glass-forming alloy Vit105 (Zr 52.5 Cu 17.9 -Ni 14.6