Characterization of Shear Bands and Cracks Induced by Three-Point Bending Fatigue Test in Zr-Cu-Al Bulk Metallic Glass

Zr50Cu40Al10 bulk metallic glass was deformed by three-point bending fatigue test in the air. Inhomogeneous shear bands/cracks were observed on the tensile and compressive regions after deformation. Characterization of shear bands by scanning electron microscopy reveals the presence of different fracture modes: river pattern and smooth fracture path on the tensile region. However, only a fracture path appears on the compressive surface. Cross sections of the shear bands/cracks were cut by focused ion beam for transmission electron microscopy (TEM) observation. Examinations of the shear band/crack microstructures reveal that nanocrystallites only appear on the crack fracture surface. Additionally, the compositions of matrix, shear band and nanocrystallite were found to be different. Shear bands contain more oxygen content but nanocrystallites have more copper content. These results are related to diffusion and thermally activated processes. The same sample tested in vacuum will be examined by TEM and the deformation mechanism will be discussed.