Endorsing Deformability of Brittle Hf-Based Bulk Amorphous Alloy by Controlling Effective Strain

Numerical finite element method (FEM) calculation results reveal that the effective strain differs between the ductile Zr-based and brittle Hf-based bulk metallic glasses (BMGs) during rolling at room temperature. The effective strain applied to BMG plates plays a key role for enabling malleability of BMGs. The current results demonstrated that the deformation mechanism of ductile Zr-based bulk metallic glass can be explained by perceptibility of multiple shear bands formation, however, the deformation mechanism of brittle Hf-based bulk metallic glass is represented by uniformly distribution of effective strain through overall specimen rather than localized into shear band. The variation of stress and the distribution of effective strain change significantly near the surface region of a Hf-based bulk metallic glass plate with increasing number of rolling passes. Under elasto-plastic deformation by cold rolling, the brittle Hf-based BMG has a thickness strain (<i>ε_t</i>) of -0.012, and the neutral effective strain (<i>ε_eff</i>) is 0.011 at the thickness direction, respectively. We present experimental confirmation that when the applied effective strain can be adjusted to below 1.1% during elasto-plastic deformation then even the brittle as-cast Hf-based BMG can be deformed up to 44% thickness reduction and 23% width expansion after multi-pass cold rolling without fracture triggered by localization of shear stress.