Scratch induced deformation behavior of hafnium based bulk metallic glass at multiple load scales

• Scratch induced deformation in Hf-BMG at micro- and macro-load scales is presented.
• Micro-scratches accommodate plastic strain by shear band and free volume generation.
• Ramp loading forms shear bands and prevents fracture in micro-scratches.
• Heat generation in the macro-scratch causes increased strain hardening.
• Complex shear band due to dual loading — normal compressive and lateral shear load

The scratch induced deformation behavior of Hafnium based bulk metallic glass (BMG) at micro- and macro-load scales is reported in this study. The micro-scratch deals with a normal load range of 1000–8000 μN, whereas the macro-scale scratches are made with a normal load reaching up to 5 N. Increase in the load beyond 2000 μN changes the deformation mechanism from plowing to fracture and chipping. The plastic strain is mostly accommodated by shear band formation with a significant amount of free volume generation. A change in the strain rate helps in the nucleation of shear bands and prevents fracture and chipping in the case of micro-scratches made at ramp loading as compared to constant load. Higher strain rate and heat generation in the track causes increased strain hardening in macro-scratch, which could be attributed to increased probability of nano-crystallization. Complex shear band structure is evolved during scratching, which is attributed to the mixed type of loading, consisting of compressive normal load and lateral shear load across scratch-track.