Bending property enhancements of Zr55Cu30Al10Ni5 bulk metallic glass: Effects of various surface modifications

Effects of various surface modifications on four-point bending property improvements of Zr55Cu30Al10Ni5 bulk metallic glass (BMG) are systematically studied. Surface modifications investigated include thin-film metallic glass coating, artificial scratches and femtosecond laser patterning. After modifications, the negligible plastic strain of 3-mm-thick BMG is found to markedly enhance to ~9.2%, without sacrificing its extraordinary strength. Instead, bending yield and fracture strengths in the surface-modified samples are increased to ~2.8 GPa and ~4.0 GPa, respectively, corresponding to a rise of ~66% from those of as-cast samples. In addition, the samples with surface modifications exhibit distinct shear band morphologies. Relationships between the shear band offset, shear band spacing and plastic strain of bent BMG samples are established. Our experimental results demonstrate that BMG is able to survive plastic flow without abrupt fracture through proper designs of surface modifications, in which large numbers of shear bands are formed to distribute the strain effectively upon loading.